Doc #101 — Tanning and Leather

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RECOMMENDED ACTIONS (BY ACTUAL URGENCY)

Phase 1 (Months 0–12)

1. Do not prioritise leather in the first weeks. NZ has existing stocks of leather goods — footwear, belts, bags, gloves — that will last years with care. Government attention should be on genuine emergencies (fuel, food, medicine). Leather production is a Phase 2 priority.
2. Include hide-related assets in the national asset census (Doc #8): Existing tanneries and their equipment, stocks of tanning chemicals (chrome salts, lime, tanning extracts), leather stocks in warehouses and retail, skilled tanners and leather workers.
3. Issue hide preservation guidance to meatworks operators. If meatworks continue operating (which they will — NZ continues processing animals for food), hides must be salted or otherwise preserved within hours of slaughter. A hide left untreated begins bacterial decay rapidly. Under normal conditions, hides are routinely preserved for export. The message is: continue preserving all hides even though there is no export market. Do not discard them.
4. Identify tannin sources. Survey black wattle (Acacia mearnsii) stands, manuka bark availability, and tanekaha bark accessibility. These become the primary inputs for vegetable tanning.

Phase 2 (Years 1–3)

5. Establish 3–5 pilot vegetable tanneries in regions with both livestock processing and tannin sources. Waikato, Canterbury, Southland, and Hawke’s Bay are strong candidates — all have meatworks, pastoral farming, and access to tannin-bearing trees.
6. Begin training tanning apprentices. Identify any remaining commercial tanners in NZ and engage them as instructors. Target: 20–50 trained tanners by end of Year 2.
7. Begin bark harvesting and tannin extraction from black wattle and other NZ sources. Fabricate bark mills (toothed steel rollers in a timber frame, requiring blacksmith or machine shop work — see Doc #92) and construct tan liquor extraction vats.
8. Establish cobbling workshops (see Doc #36) to convert tanned leather into footwear — the highest-priority end product.
9. Begin experimental brain tanning for soft leather production (garment leather, gloves). Train through heritage skills program (Doc #160).

Phase 3 (Years 3–7, ongoing)

10. Scale tanning operations to process a meaningful fraction of NZ’s annual hide output. Target: 100,000–300,000 hides per year by Year 3–5.
11. Develop harness and saddlery production as animal-drawn transport increases.
12. Establish leather grading and quality standards for different end uses.
13. Investigate tannin plantation establishment — if black wattle stands prove insufficient, dedicated plantings on marginal land.

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ECONOMIC JUSTIFICATION

3.1 The scale of the resource

NZ processes approximately 5–6 million cattle, 25–30 million sheep, and 400,000–600,000 deer per year under normal conditions.² Each animal produces a hide or skin. Under nuclear winter conditions, livestock numbers will decline as carrying capacity drops — perhaps to 50–70% of pre-event levels by Year 3 (see Doc #76). Even at reduced levels, NZ’s annual hide output is roughly:

Animal	Estimated annual slaughter (recovery)	Hides/skins per year
Cattle	2–4 million	2–4 million
Sheep	15–20 million	15–20 million
Deer	200,000–400,000	200,000–400,000
Total		17–24 million

Not all of these can or should be tanned. Tanning is labour-intensive and requires substantial tannin supply. But the raw material is not the constraint — NZ has more hides than it can realistically process.

3.2 Labour cost

A traditional vegetable tannery processing cattle hides requires approximately 2–4 person-hours per hide through the full tanning process (preparation through finishing), not counting the weeks of passive soaking time in tan liquor.³ A small tannery with 5–10 workers can process 500–2,000 cattle hides per year, producing enough sole and upper leather for approximately 1,000–4,000 pairs of boots.

Comparison with the alternative: NZ has approximately 5.2 million people who need footwear. Each person needs approximately 1–2 pairs of shoes per year under conditions of heavy physical work. Without domestic leather and shoemaking, NZ faces a footwear shortage within 3–7 years as imported shoes wear out (Doc #36). The labour investment in tanning — perhaps 200–500 full-time equivalent workers to process 200,000–500,000 hides per year — is modest relative to the consequence of a population without adequate footwear.

3.3 Opportunity cost

Tanning requires labour, timber (for bark), and workshop space. These resources compete with other manufacturing priorities. However, tanning uses relatively unskilled labour for most steps (fleshing, soaking, handling), low-technology equipment (vats, fleshing beams, drying frames), and NZ-abundant materials (hides, bark, water, lime). It does not compete heavily for machine shop time (Doc #91) or scarce technical skills. The opportunity cost is low relative to the value of the product.

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4. HIDE TYPES AND PROPERTIES

4.1 Cattle hides

Cattle hides are the most valuable for leather production.⁴

Characteristics: - Thickness: 4–7 mm raw, producing finished leather 1.5–5 mm thick depending on splitting and processing - Area: Approximately 4–5 square metres per adult hide - Strength: The strongest common leather. Suitable for boot soles (thick, firm veg-tan), boot uppers, belts, harness, industrial applications - NZ source: From beef cattle processing at meatworks throughout the country. NZ’s cattle herd is approximately 3.8 million as of the mid-2020s, predominantly beef breeds (Angus, Hereford) and dairy breeds (Friesian, Jersey).⁵

Hide quality factors: - Brand marks, barbed wire scratches, and insect damage reduce usable area. NZ cattle generally have fewer brand marks than some countries but barbed wire damage is common. - Bull hides are thicker and tougher than cow hides. Both are usable. - Dairy cow hides tend to be thinner than beef cattle hides due to breed differences and the metabolic demands of milk production.

4.2 Sheep skins

Sheep skins are smaller and thinner than cattle hides and produce a lighter, more flexible leather.⁶

Characteristics: - Thickness: 1–2 mm raw - Area: Approximately 0.4–0.8 square metres per skin - Strength: Moderate — suitable for garments, gloves, linings, light bags, bookbinding. Not strong enough for boot soles or heavy harness. - Wool-on skins: Sheepskins can be tanned with the wool left on, producing woolskin rugs and garment linings. NZ already has some capability in this area. Woolskin garment linings are excellent insulation for boots and winter clothing. - NZ source: Abundant — NZ processes approximately 25–30 million sheep per year under normal conditions.⁷

4.3 Deer hides

Deer hides produce a distinctive leather — soft, strong, and durable.⁸

Characteristics: - Thickness: 1–3 mm raw - Area: Approximately 1–2 square metres per hide - Strength: Good — stronger than sheep, lighter than cattle. Historically prized for gloves, garments, and moccasin-style footwear - NZ source: NZ has approximately 850,000 farmed deer (predominantly red deer, Cervus elaphus) plus a significant wild deer population (red deer, fallow deer, sika, and others).⁹ Wild deer hunting (Doc #82) provides hides as a by-product.

4.4 Other hides available in NZ

• Goat skins: NZ has a small farmed goat population plus significant feral goat numbers. Goatskin produces fine, strong leather (known as morocco or kid leather). Good for gloves, bookbinding, and garment leather.
• Pig skins: From NZ’s pig farming industry. Pig leather is porous and not waterproof but is soft and durable. Used for gloves, bags, and some garment applications.
• Rabbit skins: NZ has large wild rabbit populations. Rabbit skin is fragile and cannot be tanned into structural leather, but fur-on rabbit skins make warm garment linings and can be pieced together into fur garments.
• Possum skins: Abundant from pest control (Doc #82). Very small — useful for fur-on garments but too small and thin for structural leather.

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5. HIDE PRESERVATION

5.1 The urgency of preservation

A raw hide begins decomposing within hours of the animal’s death. Bacteria attack the protein (collagen) structure of the hide, and decay is accelerated by warmth and moisture. If a hide is not preserved within 4–6 hours in warm conditions (or 12–24 hours in cold conditions), it may become unusable for tanning.¹⁰

This is the most time-critical step in the entire leather production chain. Every other step can wait days, weeks, or months. Hide preservation cannot.

Under normal NZ conditions, meatworks routinely salt hides immediately after flaying. This practice must continue. The critical action for the recovery period is communicating to meatworks operators and farm slaughterers that all hides should be preserved, even though the export market no longer exists.

5.2 Preservation methods

Wet salting (preferred): The standard commercial method. Hides are spread flesh-side up and covered with coarse salt (approximately 30–40% of hide weight in salt).¹¹ Salt draws moisture from the hide through osmosis, creating conditions inhospitable to bacteria. A properly salted hide can be stored for months to years if kept cool and dry.

• Salt requirement: Approximately 3–5 kg of salt per cattle hide, 0.5–1 kg per sheep skin. NZ can produce salt domestically (Doc #103 — sea salt production). The total salt requirement for hide preservation is significant but manageable — perhaps 1,000–3,000 tonnes per year if processing 200,000–500,000 cattle hides.
• Storage: Salted hides should be stacked flesh-side up with additional salt between layers. Stored in a cool, covered, well-ventilated area. Drainage must be provided — brine runs off as salt pulls moisture from the hides.

Drying (air-drying or frame-drying): Hides stretched on frames or pegged out and dried in air. Works in dry, cool climates. Less reliable in NZ’s humid conditions, particularly on the West Coast and during winter. Dried hides become stiff and hard (rawhide) and must be rehydrated before tanning. Air-drying is a viable backup method but salt curing is preferred for NZ conditions.¹²

Freezing: If cold storage is available (electricity-powered freezers are functional under the baseline scenario), freezing preserves hides indefinitely. This is practical for small quantities but not scalable for the full national hide output — the freezer space is better used for food.

Smoking: Light smoking inhibits bacterial growth and can supplement other preservation methods. Traditional practice in some cultures. Not sufficient alone but can extend the working time before salting.

5.3 Hides from non-meatworks sources

Under recovery conditions, more animals will be slaughtered on-farm or in community settings rather than at centralised meatworks. These hides are at risk of being discarded because farmers may lack salt, knowledge, or motivation to preserve them. Community education and salt distribution to farming areas are practical measures.

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6. HIDE PREPARATION (BEAM HOUSE OPERATIONS)

Before tanning can begin, the raw hide must be cleaned and prepared. These steps collectively take 1–4 weeks and transform a raw, salted hide into a clean, prepared hide ready for tanning.¹³

6.1 Soaking

Salted or dried hides are soaked in clean water for 24–48 hours to rehydrate them and wash out salt, blood, and dirt. Water should be changed at least once. In cold conditions (nuclear winter), soaking may take longer — up to 72 hours.

6.2 Liming

The most important preparation step. Hides are soaked in a lime solution (calcium hydroxide, Ca(OH)2 — also called slaked lime) for 1–3 weeks.¹⁴

Liming achieves several things: - Loosens the hair and epidermis, allowing them to be scraped off - Swells the hide, opening up the collagen fiber structure for tannin penetration - Removes some of the non-structural proteins - Raises the pH, which preserves the hide during the preparation period

Lime source for NZ: Calcium oxide (quicklime, CaO) is produced by heating limestone (calcium carbonate, CaCO3) in a kiln to approximately 900–1,000 degrees C. NZ has substantial limestone deposits — Golden Bay (Tasman), Otorohanga (Waikato), Oamaru (North Otago), and elsewhere — and existing lime production capacity. Quicklime is slaked (mixed with water) to produce calcium hydroxide for the liming solution. Lime production is covered in Doc #112 (cement and concrete) — the same raw material and kiln technology serves both purposes.

Lime solution: Approximately 5–10% calcium hydroxide in water. Hides are suspended in the solution or layered in a vat with lime paste between them. The solution is agitated periodically (stirring with a pole, or the hides are moved between vats of increasing strength).

6.3 Fleshing

After liming, the swollen hide is draped over a curved wooden beam and the flesh side is scraped with a two-handled fleshing knife to remove remaining fat, flesh, and membrane. This is skilled physical work — applying consistent pressure to remove tissue without cutting into the hide itself. Fleshing is one of the steps where training matters most.

Tools: A fleshing beam (a curved wooden beam approximately 1.5 metres long, 300–400 mm diameter, set at a comfortable working height) and a fleshing knife (a two-handled blade with a slightly concave edge, approximately 300–400 mm wide). Both can be made from NZ materials — timber beam, steel blade (Doc #92, Doc #91).

6.4 Dehairing (unhairing)

The loosened hair and epidermis are scraped off using the same beam and a slightly different scraping tool (the unharing knife has a blunter edge than the fleshing knife). After liming, the hair should pull away relatively easily. The scraped hair has some value — animal hair was historically used for plaster reinforcement, upholstery stuffing, and felt-making.¹⁵

6.5 Deliming and bating

After fleshing and dehairing, the lime must be partially removed before tanning:

Deliming: Washing the hide in water to remove excess lime. This can be accelerated by adding a mild acid — vinegar (acetic acid, from ethanol production, Doc #51) works. The goal is to reduce the pH from the strongly alkaline liming range (pH 12–13) to a mildly acidic or neutral range suitable for tanning (pH 3–6 for vegetable tanning).¹⁶

Bating: Traditionally, bating was accomplished by soaking the delimed hide in a solution of animal dung (particularly pigeon or dog dung), which contains enzymes that soften the hide and remove remaining non-structural proteins.¹⁷ This produces a more supple leather. Modern commercial bating uses purified enzymes (pancreatin, trypsin) — imported consumables that will deplete.

NZ options for bating: - Animal dung bating — unpleasant but effective. Pigeon dung is considered the best traditional bating agent. Cattle dung is usable but less effective. - Soaking in a weak solution of animal pancreas extract — the pancreas contains the same enzymes used commercially. This requires access to animal offal from meatworks, which NZ has in abundance. - For sole leather and heavy leather where suppleness is less important, bating can be reduced or skipped entirely. The leather will be stiffer but functional.

6.6 Pickling (optional)

For some tanning methods, the prepared hide is “pickled” by soaking in a solution of salt and acid (typically sulfuric acid or formic acid) to further lower the pH and prepare the collagen for tanning. This is standard practice for chrome tanning and some vegetable tanning processes. Sulfuric acid availability depends on Doc #113. For basic bark tanning, pickling is not strictly necessary — the acid in the tan liquor itself adjusts the pH gradually.

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7. TANNING METHODS

7.1 Vegetable tanning — the primary NZ method

Vegetable tanning uses tannin extracted from plant materials — primarily tree bark — to convert prepared hide into leather. Tannin molecules bind to the collagen fibers, stabilising them against bacterial decay, heat, and moisture. This is the oldest tanning method, used for at least 5,000 years, and it remains the most feasible method for NZ under recovery conditions.¹⁸

NZ tannin sources (ranked by suitability):

Source	Tannin content (% dry bark weight)	Availability in NZ	Notes
Black wattle (Acacia mearnsii)	35–45%	Moderate — planted in forestry blocks, shelterbelts, and naturalised stands in both islands, particularly warmer northern and eastern regions	Among the world’s best commercial tannin sources. Bark from trees 7–10+ years old gives highest tannin. Bark harvesting does not require killing the tree if done carefully (partial bark stripping), though it is most efficient when combined with timber harvesting.19
Tanekaha (Phyllocladus trichomanoides)	15–25% (estimated)	Moderate — native conifer found in lowland and montane forest throughout North Island and northern South Island	Traditional Maori tanning agent. Bark produces a reddish-tan colour. Slow-growing native tree — harvesting must be sustainable. Bark can be collected from wind-fallen trees or from forestry clearance.20
Manuka (Leptospermum scoparium)	10–20% (estimated)	Abundant — one of NZ’s most common shrub/small trees, found throughout the country	Lower tannin concentration than wattle, but extreme abundance partly compensates. Bark and wood can be used. Harvesting is straightforward — manuka is often cleared for pasture or forestry and the bark is a by-product.21
Radiata pine (Pinus radiata) bark	5–15%	Very abundant — NZ’s dominant plantation tree, approximately 1.7 million hectares planted	Lower tannin concentration, but the sheer volume of bark available from sawmilling operations makes this a significant potential source. Pine bark tannin produces a darker leather than wattle.22
Kanuka (Kunzea ericoides)	8–15% (estimated)	Common throughout NZ	Similar to manuka but typically lower tannin content. Usable as a supplementary source. Tannin content estimates require local empirical testing.23
Native beech (Nothofagus spp.)	10–20% (estimated)	Extensive forests in South Island, southern North Island	Bark contains tannin. Beech forests are extensive but access may be limited in rough terrain. Tannin content estimate based on general Nothofagus chemistry; NZ-specific data is limited.24

Process — pit tanning (traditional method):

1. Bark preparation: Bark is stripped from trees, dried, and ground or shredded into small pieces. A bark mill — two toothed or corrugated steel rollers crushing bark between them, driven by a hand crank, water wheel, or electric motor — is the standard tool. Fabricating a bark mill requires a blacksmith or machine shop: steel rollers (cast or fabricated), a sturdy timber or steel frame, bearings, and a drive shaft. This is not complex compared to other industrial tooling but it is not improvised — see Doc #92 (blacksmithing) and Doc #91 (machine shop). Ground bark increases surface area for tannin extraction.
2. Tan liquor preparation: Ground bark is soaked in water in a vat or pit. Over days to weeks, tannin leaches into the water, producing a dark brown solution — the tan liquor. Fresh bark is added periodically to strengthen the solution. Old, exhausted bark is removed and replaced.
3. Initial tanning (weak liquor): Prepared hides are placed in a weak tan liquor (approximately 1–3% tannin) for 1–2 weeks. Starting with weak liquor prevents the surface of the hide from tanning too fast and blocking tannin penetration into the interior — a fault called “case-hardening.”²⁵
4. Progressive tanning (pit layering): Hides are transferred to progressively stronger tan liquor over several weeks. In traditional pit tanning, hides are layered in pits with ground bark between each layer, and the pit is filled with tan liquor. Hides remain in the pit for 3–12 months depending on hide thickness and the strength of leather required. Sole leather (the thickest, firmest grade) requires the longest tanning — up to 12–18 months for full penetration of a heavy cattle hide.²⁶
5. Testing: Tanning completion is checked by cutting a small sample from the edge of the hide and examining the cross-section. Fully tanned leather shows uniform colour throughout the cross-section. If the centre is still white or grey, tanning is incomplete.

Timeline: Vegetable tanning is slow. A cattle hide for boot soles requires 6–18 months of tanning. Lighter leathers (upper leather, garment leather from sheep or deer skins) can be tanned in 4–8 weeks using stronger liquor and thinner hides. This is the single largest practical difference from modern chrome tanning (which takes hours to days). Planning must account for this lead time — hides placed in tanning vats today produce usable leather months from now.

Infrastructure required: - Tanning pits or vats (timber-lined pits in the ground, or wooden or concrete vats). A small tannery needs 10–20 vats of varying sizes. - Bark mill (fabricated in a machine shop or by a blacksmith) - Fleshing beams and knives - Drying frames or racks - Water supply (tanning requires large volumes of water, and spent tan liquor must be disposed of — downstream from water intakes, away from drinking water) - Covered workspace (tanning can be done outdoors in mild weather, but rain and direct sun affect the process)

7.2 Brain tanning

Brain tanning uses emulsified animal brains as the tanning agent. The fats and phospholipids in the brain penetrate the collagen fibers and coat them, producing a soft, supple leather (traditionally called buckskin when made from deer hide).²⁷

Process:

1. Prepare the hide as for vegetable tanning (soak, lime or ash-soak, flesh, dehair, delime)
2. Mash the animal’s brain in warm water to create an emulsion. A widely repeated rule of thumb holds that every animal has enough brains to tan its own hide — a saying that approximately holds for thin-to-medium hides (deer, sheep) but is unreliable for thick cattle hides, where supplementing with brains from other slaughtered animals may be necessary.²⁸ Approximately 300–500 grams of brain emulsion is used per cattle hide; deer and sheep hides require proportionally less
3. Work the brain emulsion into the hide by hand, rubbing and kneading. Allow it to soak in for several hours to overnight
4. Stretch and work the hide continuously as it dries. This is the labour-intensive step — the hide must be physically stretched, pulled, and flexed throughout the drying process to prevent the fibers from bonding together as they dry. If the hide is allowed to dry without working, it becomes stiff rawhide rather than soft leather
5. Smoke the finished leather over a smouldering fire (typically using punky or rotten wood that produces smoke without excessive heat). Smoking deposits aldehydes into the leather that provide additional tanning action and water resistance. Unsmoked brain-tanned leather will stiffen again if it gets wet; smoked brain-tanned leather remains supple

Assessment: - Advantages: No imported chemicals needed. No specialised equipment. Produces the softest leather achievable without chrome tanning. Suitable for garments, gloves, moccasins, and any application requiring flexibility. - Disadvantages: Very labour-intensive — a single cattle hide requires 8–16 hours of continuous physical working during drying. Not suitable for thick sole leather (brain tanning does not penetrate thick hides well). Not water-resistant unless smoked. Lower durability than vegetable-tanned leather for high-wear applications. - Best applications: Deer and sheep hides for garment leather, gloves, moccasin uppers. Not for boot soles or heavy-duty use.

7.3 Oil tanning (chamois)

Oil tanning uses fish oil, animal fat, or other oils to tan leather. The traditional “chamois” leather is made this way.²⁹

Process: 1. Prepare the hide (lime, flesh, dehair, delime, split to desired thickness) 2. Work fish oil or cod liver oil into the damp hide by hand or by fulling (mechanical pounding) 3. Hang in a warm place. Oxidation of the oil cross-links with the collagen fibers, producing a soft, absorbent leather 4. Repeat oiling and oxidation until the leather is fully tanned (several cycles over 1–2 weeks)

NZ oil sources: - Fish oil from NZ’s fishing industry (hoki, barracouta, and other oily species) - Whale oil — if whaling is resumed under recovery conditions, whale oil is an excellent tanning agent. This is a governance and ethical question beyond the scope of this document. - Tallow (rendered beef or sheep fat) — partially effective as a tanning oil but produces a greasier, less durable leather than fish oil

Assessment: Oil-tanned leather is soft, absorbent, and washable — excellent for cleaning cloths, filtration, gaskets, and light garments. It is not strong or durable enough for footwear or heavy-duty applications. A useful complement to vegetable tanning, not a replacement.

7.4 Chrome tanning — limitations under NZ conditions

Chrome tanning, which uses chromium(III) sulfate (Cr2(SO4)3) as the tanning agent, is the dominant modern tanning method. It is fast (hours to days rather than months), produces soft, flexible leather, and accounts for approximately 80–90% of global leather production.³⁰

NZ cannot sustain chrome tanning. Chromium sulfate is an imported chemical, and NZ has no known significant chromium ore deposits.³¹ Existing stocks of chrome tanning chemicals in NZ tanneries are finite — probably sufficient for months to a few years of limited production at most, depending on what was in stock at the time of the event.

Practical approach: Use existing chrome tanning chemical stocks while they last, primarily for applications where soft, flexible leather is most needed (shoe uppers, garment leather). Transition to vegetable and brain tanning as chrome stocks deplete. This transition should be planned, not reactive — begin vegetable tanning operations in parallel with chrome tanning from the start, so that capability is established before chrome stocks run out.

Trade potential: If maritime trade develops with Australia or other regions, chromium compounds might be obtainable. Australia has chromite deposits (in Queensland and Western Australia). This is uncertain and should not be relied upon for planning.

7.5 Alum tanning (tawing)

Alum tanning (traditionally called tawing) uses aluminium salts — typically potassium alum (potassium aluminium sulfate, KAl(SO4)2) — to produce white, soft leather.³²

NZ alum sources: NZ has geothermal deposits that contain alunite and other aluminium-bearing minerals, particularly in the Taupo Volcanic Zone.³³ Alum can also be produced from kaolin (china clay, of which NZ has deposits in Northland and parts of the South Island).³⁴ The chemical process to extract alum from mineral sources is feasible but requires acid dissolution and crystallisation capability — it is not trivial. Alum is also used in water treatment and other applications.

Assessment: Alum tanning produces a white leather that is soft when dry but stiffens and loses its tanning if soaked in water — technically, alum tawing is not a true tanning process (the treatment is reversible).³⁵ Historically used for fine gloves, bookbinding, and decorative leather. Not suitable for footwear or any application involving water exposure. A specialist method, not a primary tanning process.

7.6 Combination tanning

In practice, the best results may come from combining methods:

• Vegetable-tanned sole leather for boot soles and heavy-duty applications
• Semi-vegetable-tanned upper leather with shorter tan times and finishing with oil or fat to improve flexibility
• Brain-tanned deer or sheep skin for gloves, garment leather, and soft applications
• Oil-tanned leather for gaskets, cleaning cloths, and filtration
• Chrome-tanned leather from remaining chemical stocks for high-quality shoe uppers while stocks last

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8. FINISHING AND POST-TANNING TREATMENT

8.1 Drying

After tanning, leather must be dried carefully. Improper drying causes cracking, warping, and hardening.³⁶

Methods: - Air drying: Hang or stretch on frames in a well-ventilated, shaded area. Avoid direct sun (causes surface hardening) and excessive heat. Drying takes 1–5 days depending on leather thickness and humidity. Under nuclear winter conditions (cooler, possibly more humid), drying times will be longer. - Pole drying: Draping wet leather over smooth wooden poles in a drying shed. A traditional method that allows air circulation on both sides. - Frame drying: Stretching the hide on a wooden frame with toggles or nails. Prevents shrinkage and keeps the leather flat. Preferred for larger hides.

8.2 Fat liquoring (oiling)

Dried leather — particularly vegetable-tanned leather — is stiff. Fat liquoring restores flexibility by introducing oils and fats into the fiber structure.³⁷

NZ-available fat liquoring agents: - Tallow: Rendered beef or sheep fat. The most abundant option. Applied warm (melted) by rubbing into the grain and flesh sides. Tallow alone produces a functional but somewhat heavy leather. - Lanolin: Recovered from wool scouring (Doc #34). An excellent leather conditioner — lanolin is the natural grease from sheep’s wool and penetrates leather well. Produces a softer finish than tallow. - Fish oil: Good penetration. Produces flexible leather. NZ source from the fishing industry. - Neatsfoot oil: Traditionally made by boiling cattle shin bones and hooves. Widely considered one of the best leather conditioning oils. NZ can produce this — cattle bones and hooves are a meatworks by-product.³⁸

Process: Apply warm oil or fat to the damp (not fully dry) leather by hand, working it into both surfaces. Allow it to absorb, then hang to complete drying. Multiple applications may be needed for thick leather.

8.3 Currying

Currying is the traditional finishing process that converts tanned leather into a flexible, workable material. It combines fat liquoring with physical working — the leather is staked (pulled over a blunt blade or edge to flex and soften the fibers), then oiled, then staked again. A well-curried vegetable-tanned leather is flexible, strong, and durable. Currying is a distinct skill from tanning — historically, tanners and curriers were separate trades.³⁹

8.4 Dyeing

Vegetable-tanned leather has a natural tan to brown colour. For different colours:

• Black: Iron liquor (ferrous sulfate or iron acetate) applied to vegetable-tanned leather reacts with the tannin to produce a deep black. Iron liquor is made by soaking iron nails or filings in vinegar for several days. This is the traditional method for black leather and works well.⁴⁰
• Brown (darker): Additional applications of strong tan liquor deepen the natural tan. Different bark sources produce different shades — manuka and wattle produce reddish-brown; pine bark produces darker brown.
• Red-brown: Tanekaha bark produces a distinctive reddish colour traditionally used in Maori leather and fiber dyeing.⁴¹
• Other colours: More difficult without synthetic dyes. Natural dyes used on textiles (Doc #36) can be applied to leather, but adhesion and fastness are generally poorer than on wool or cotton.

8.5 Surface finishing

• Grain finishing: The outer (hair) side of the leather — the grain — can be polished, buffed, or coated to improve appearance and water resistance. Traditional finishes include beeswax, tallow, and shellac (from lac — not available in NZ). Beeswax finish produces an attractive, water-resistant surface.
• Dubbin: A traditional waterproofing compound for leather, made from tallow and beeswax (melted together in approximately 2:1 ratio). Applied to boots and outdoor leather to maintain suppleness and repel water. NZ can produce both tallow and beeswax.⁴²

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9. LEATHER PRODUCTS — PRIORITY APPLICATIONS

9.1 Footwear (highest priority)

Covered in detail in Doc #36, Section 7. Sole leather requires thick (4–6 mm), firm, heavily vegetable-tanned cattle hide. Upper leather requires thinner (1.5–2.5 mm), more flexible leather — vegetable-tanned with thorough fat liquoring, or chrome-tanned while stocks last, or brain-tanned deer or sheep skin for lighter footwear.

Performance gap — sole leather: Vegetable-tanned leather soles wear faster than rubber soles on hard surfaces (Doc #36 estimates 3–6 months of heavy use versus 1–3 years for rubber). Hobnails extend leather sole life significantly. This is the most important limitation of NZ-produced footwear relative to pre-war standards.

9.2 Harness and saddlery

As transport shifts toward animal-drawn vehicles (Doc #33, Section 6), demand for harness leather increases. Harness leather is heavy, strong, vegetable-tanned cattle hide — the same basic product as boot sole leather but cut and assembled differently. A single horse harness set requires approximately 5–8 square metres of leather.⁴³

Saddlery requires both heavy leather (for the tree covering and skirts) and lighter, flexible leather (for seats and fenders). Saddlers are a distinct trade from cobblers — NZ has some saddlery practitioners, primarily serving the equestrian community. The skills census (Doc #8) should identify them.

9.3 Belts and straps

Simple but essential products. Leather belts replace synthetic webbing and elastic. Leather straps serve countless utility functions — tool attachments, pack straps, equipment fastening. These are among the easiest leather products to make and could be produced at community scale with minimal training.

9.4 Industrial leather

Before synthetic materials, leather was used extensively in industrial applications:⁴⁴

• Pump washers and gaskets: Leather cup washers for hand pumps and piston pumps. Thick, firm, vegetable-tanned leather soaked in tallow.
• Drive belts: Flat leather belts for power transmission from line shafts to individual machines. This was standard in factories until electric motors allowed individual machine drive. If any belt-driven equipment is reactivated, leather belting is the most feasible replacement material.
• Bellows: For blacksmith forges (Doc #92), furnaces, and organ-type blowers. Bellows leather must be thin, flexible, and airtight — well-fat-liquored vegetable-tanned or oil-tanned leather.
• Valve leather: For pumps and other mechanical equipment.

9.5 Protective clothing

• Aprons: For blacksmiths, welders, farriers, and other hot-work trades. Thick leather aprons protect against sparks and hot metal.
• Gloves: Work gloves from vegetable-tanned or brain-tanned leather. Welding gloves from thick cattle hide.
• Chaps and gaiters: Leg protection for bush work, fencing, and agriculture.

9.6 Bookbinding

Leather-bound books are more durable than paper-covered ones — relevant for Recovery Library documents and other critical reference materials intended for decades of heavy use.⁴⁵ Sheep or goat skin, vegetable-tanned and alum-treated, is the traditional bookbinding leather.

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10. RAWHIDE — UNTANNED BUT USEFUL

Not all hide applications require tanning. Rawhide — cleaned, stretched, and dried hide without tanning — has its own uses:⁴⁶

• Lashing and binding: Rawhide strips, soaked in water to soften, can be wrapped around joints and connections. As the rawhide dries, it shrinks and tightens, creating an extremely strong binding. Used historically for axe heads, tool handles, and drum heads.
• Drum heads and membrane applications
• Dog chews (a minor use but reflects the material’s availability)
• Emergency repairs: Rawhide applied wet and dried over a break creates a strong temporary splint or reinforcement.

Limitation: Rawhide softens when wet and is vulnerable to bacterial decay if not kept dry. It is not a substitute for tanned leather in applications involving moisture exposure.

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11. WASTE PRODUCTS AND BY-PRODUCTS

Tanning produces several useful by-products:⁴⁷

• Hair: Scraped from hides during dehairing. Usable as plaster reinforcement (mixed into lime plaster), upholstery stuffing, and felt-making.
• Fleshing and trimmings: Fat and protein scraped from hides. Rendered for tallow (Doc #34, Doc #37). Protein residue can be composted or used as animal feed supplement (in limited quantities).
• Hide glue: Made by boiling leather scraps, trimmings, and unusable hide pieces in water for several hours. The collagen dissolves and the resulting liquid sets into a strong adhesive when cooled. Hide glue was the primary woodworking adhesive for centuries before synthetic glues. NZ has abundant feedstock for hide glue production (Doc #47).⁴⁸
• Spent tan liquor: The used tanning solution still contains tannin and organic matter. It can be strengthened with fresh bark and reused. Eventually, exhausted liquor must be disposed of — it is acidic and contains suspended organic matter. Disposal should be to land (irrigation on pasture absorbs the nutrients) rather than to waterways.
• Spent bark: Exhausted bark from tannin extraction retains some value as mulch, fuel, or composting material.

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12. TANNERY SCALE AND LOCATION

12.1 Small-scale community tannery

A community-scale tannery serving a district of 5,000–20,000 people might process 500–2,000 hides per year and employ 3–8 workers (tanners, fleshers, curriers).

Space requirements: 200–500 square metres of covered or semi-covered workspace plus outdoor drying area. Adjacent to a water source (stream or piped water). At least 100 metres from residential areas — tanning produces strong odours during liming and bating.

Equipment (all fabricable in NZ):

Item	Materials	Fabrication
Soaking/liming vats (×4–6)	Timber planks or concrete	Carpentry or masonry
Tanning pits (×6–10)	Timber-lined earth pits or concrete vats	Excavation and carpentry
Fleshing beams (×2–3)	Hardwood log, smoothed	Basic woodwork
Fleshing and dehairing knives (×4–6)	Steel, hardwood handles	Blacksmithing (Doc #92)
Bark mill (×1)	Steel rollers, timber frame	Machine shop (Doc #92)
Drying frames (×20–30)	Timber and pegs or toggles	Carpentry
Currying table and stake	Timber, steel blade	Carpentry and blacksmithing

12.2 Regional tannery

A larger operation processing 5,000–20,000 hides per year, employing 15–40 workers. Serves a regional population and produces leather for regional cobbling workshops, saddleries, and industrial users.

Additional requirements over community scale: - Mechanical bark crushing (motor-driven bark mill) - Larger vat arrays (some tanneries historically used rotating drums for faster tanning — a drum rotates the hides in tan liquor, reducing tanning time by 30–50% compared to static pit tanning) - More sophisticated fat liquoring and finishing capability - Quality grading capability

12.3 Recommended locations

Tanneries should be sited where livestock processing, tannin sources, water, and transport all converge:

Region	Livestock processing	Tannin source	Water	Notes
Waikato	Major meatworks	Manuka, radiata pine bark	Abundant rivers	Strong candidate for North Island
Hawke’s Bay	Meatworks, pastoral farming	Black wattle, manuka	Adequate	Good climate for drying
Canterbury	Major meatworks	Radiata pine bark, beech	Adequate	Strong candidate for South Island
Southland	Meatworks, high sheep numbers	Beech, manuka	Abundant	Cold climate slows outdoor processes; indoor facilities needed
Taranaki	Dairy processing (cattle hides)	Radiata pine bark	Abundant

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13. THE QUALITY GAP — HONEST ASSESSMENT

NZ-produced leather under recovery conditions will not match the quality, consistency, or variety of pre-war commercial leather. Understanding the gap helps planners and users set realistic expectations.

13.1 What NZ can produce well

• Heavy sole leather: Thick, firm, vegetable-tanned cattle hide for boot soles and heavy-duty applications. This is the product that vegetable tanning excels at. Quality can approach historical benchmarks — before chrome tanning, all boot sole leather was vegetable-tanned, and it was excellent.
• Harness and strap leather: Strong, durable, moderately flexible. Vegetable-tanned and curried. Another traditional strength of bark tanning.
• Rawhide products: Effectively equivalent to any historical standard.
• Woolskins: NZ already has some capability in this area. Sheep skins tanned with wool attached for boot linings, garment linings, and rugs.

13.2 What NZ can produce adequately

• Boot upper leather: Vegetable-tanned and well fat-liquored cattle or deer hide. Functional but noticeably stiffer than chrome-tanned upper leather — vegetable-tanned uppers require a break-in period of weeks of wear before conforming to the foot, versus the immediate comfort of chrome-tanned leather. Extended fat liquoring and mechanical staking reduce but do not eliminate this gap.⁴⁹ Adequate for work boots; not as comfortable as modern chrome-tanned shoes for initial wear.
• Garment leather: Brain-tanned deer or sheep skin. Soft and attractive but less uniform and less durable than commercial garment leather — brain-tanned leather loses suppleness if repeatedly soaked and dried without re-smoking, and batch-to-batch colour variation is significant. Adequate for gloves, jackets, and similar applications.
• Belt and bag leather: Good quality achievable.

13.3 What NZ will struggle with

• Soft, uniform shoe upper leather matching chrome-tanned commercial leather — this is the biggest quality gap. Vegetable-tanned upper leather requires extended fat liquoring and working to approach the flexibility of chrome leather, and even then falls short.
• Waterproof leather matching modern waterproof boot treatments. Dubbin and tallow help but do not match synthetic waterproofing.
• Consistent colour and finish across large batches. Vegetable tanning with natural bark produces variable colour depending on bark quality, tanning duration, and processing. Leather will be less uniform than commercial product.
• Thin, flexible leather for fashion applications. This is a low priority but worth noting — NZ’s leather will be utilitarian, not fashion-grade.

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14. CRITICAL UNCERTAINTIES

Uncertainty	Impact	Mitigation
Volume and distribution of black wattle in NZ	Directly determines vegetable tanning capacity. If wattle is scarce, alternative tannin sources (manuka, pine bark) must carry the load, requiring more bark per hide due to lower tannin content.	Survey through national asset census (Doc #8). Begin immediately.
Number and capability of existing NZ tanners	Determines training capacity and initial production speed	Skills census. Engage any identified tanners as instructors.
Chrome tanning chemical stocks in NZ	Determines how long chrome tanning can supplement vegetable tanning	Inventory through asset census. Ration for highest-value applications.
Tanning time for NZ bark sources under NZ conditions	Published tannin content data is for global species, not necessarily NZ-grown specimens. Actual tanning time with NZ wattle bark requires empirical testing.	Begin pilot tanning operations early. Test multiple bark sources.
Hide quality from NZ livestock under nuclear winter stress	Animals under nutritional stress may produce thinner, weaker hides	Monitor hide quality as conditions change. Adjust tanning parameters.
Salt availability for hide preservation	If salt production (Doc #103) is insufficient, hide preservation is constrained	Prioritise salt for preservation over other uses if needed.
Water pollution from tannery waste	Tanning produces acidic, odorous waste water. Improper disposal contaminates waterways	Site tanneries away from drinking water. Use land disposal of spent liquor.
Labour availability for the intensive working required in brain tanning	Brain tanning is extremely labour-intensive. Competing labour demands may limit production	Reserve brain tanning for high-value soft leather applications. Use vegetable tanning for bulk production.

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15. CROSS-REFERENCES

Dependencies — inputs this document requires:

• Doc #036 — Clothing and Footwear — Primary downstream consumer of leather. Tanning depends on a functioning cobbling and saddlery trade to convert leather into usable products; without footwear workshops, tanned leather has no outlet. Sole leather specs and production targets are driven by Doc #036 footwear requirements.
• Doc #074 — Pastoral Farming — Tanning depends entirely on the animal supply. Hide volume, quality, and distribution are direct outputs of the pastoral farming system. Nuclear winter effects on livestock carrying capacity (Doc #074) set the upper bound on annual hide availability.
• Doc #085 — Animal Breeding — Longer-term hide quality and quantity depend on breeding decisions. Breed selection for meat-focused traits (Angus, Hereford) produces thicker, better-quality hides than dairy-focused breeds. Animal breeding priorities affect the tanning industry’s raw material base over a 3–10 year horizon.
• Doc #047 — Adhesives — Hide glue, a tanning by-product (from scraps and offcuts boiled in water), is a primary structural adhesive for woodworking and bookbinding. Doc #047 covers adhesive production including hide glue; there is a direct feedstock relationship — tannery waste supplies the glue-making operation.
• Doc #102 — Charcoal Production — Bark tanning requires heat for bark drying, tan liquor warming in cold conditions, and hide-processing workshops. Where grid power is unavailable, charcoal is the fuel source for these operations. Doc #102 also covers the bark-combustion relationship — spent exhausted bark from tannin extraction can fuel charcoal retorts.
• Doc #113 — Sulfuric Acid Production — Sulfuric acid is used in pickling (preparing hides for tanning) and is the basis for chrome tanning chemicals (chromium sulfate). Where sulfuric acid can be produced domestically, it extends the viability of chrome tanning beyond imported stock depletion and improves vegetable tanning process control. Doc #113 is a partial alternative to full import dependence for chrome tanning.

Related documents — shared supply chains and downstream consumers:

• Doc #033 — Tires — Parallel rubber constraint. Leather soles are the primary substitute for rubber shoe soles; the same livestock supply chain underlies both.
• Doc #034 — Lubricant Production — Tallow and lanolin serve both as leather finishing agents and as lubricants. Shared pastoral by-product supply.
• Doc #037 — Soap and Hygiene — Tallow from hide fleshing is soap feedstock. Shared rendering supply chain.
• Doc #082 — Hunting and Wild Harvest — Wild deer, goat, and pig hides from hunting supplement farmed livestock hides.
• Doc #091 — NZ Steel / Machine Shop Operations — Steel for tanning tools (fleshing knives, bark mill components, vat fittings) and fabrication of bark mills and tanning equipment.
• Doc #092 — Blacksmithing — Production of fleshing knives, currying tools, and hand tools for leather working.
• Doc #097 — Cement and Concrete — Lime production from limestone provides calcium hydroxide for hide liming; same kilns serve both purposes.
• Doc #100 — Harakeke Fiber — Harakeke complements leather in some applications (stitching thread from muka, combined leather-and-harakeke products).
• Doc #103 — Salt Production — Salt is a critical input for hide preservation; without adequate salt, hides decay before reaching the tannery.
• Doc #104 — Clothing and Textiles — Leather garment components (gloves, aprons, reinforcing panels) integrate with textile clothing production. Tanning and textile trades share the pastoral by-product supply chain (wool, hides, tallow from the same animals).
• Doc #156 — Census — Identifies tanning assets, bark sources, skilled tanners, and leather stocks.
• Doc #157 — Trade Training — Tanning, currying, cobbling, and saddlery should be included in trade training curricula.
• Doc #160 — Heritage Skills Preservation — Traditional leather working skills, if held by older practitioners, must be captured before they are lost.

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16. SUMMARY

NZ has more raw hides than it can process — the constraint is not material but capability. Rebuilding a tanning industry requires training people, fabricating the necessary equipment (bark mills, tanning vats, fleshing beams, currying tools — achievable in NZ machine shops and blacksmith forges), securing tannin sources (primarily black wattle bark), and accepting the slow tempo of vegetable tanning (months per batch, not days).

The dependency chain is manageable and almost entirely domestic: hides from NZ livestock, tannin from NZ trees, lime from NZ limestone, salt from NZ sea water, fat for finishing from NZ animals, water from NZ rivers. The only significant imported input is chrome tanning chemicals, and these can be replaced — at the cost of slower production and stiffer leather — by vegetable and brain tanning methods that served humanity for thousands of years before chrome tanning was invented in the 1850s.

The quality gap is real. NZ-produced leather will be less consistent, less soft (for most applications), and less varied than pre-war commercial leather. Footwear made with vegetable-tanned soles will wear faster than rubber-soled shoes. These are genuine limitations. They are also manageable — the alternative is not “slightly less convenient leather” but “no leather at all,” and a population without footwear or harness or belts or gaskets faces far worse problems than stiff shoes.

Tanning should begin at pilot scale in Phase 2 (Year 1) and scale progressively. The long lead time of vegetable tanning means that hides placed in the tanning pits in Month 6 produce usable sole leather by Month 12–18 — starting early is not premature, it is necessary. By Year 3–5, NZ should have enough tanning capacity to supply regional cobbling workshops (Doc #36), saddleries, and industrial leather users with domestically produced leather of adequate quality for all essential applications.

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FOOTNOTES

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1. NZ livestock numbers: Stats NZ and Ministry for Primary Industries. As of the mid-2020s, NZ had approximately 3.8 million cattle (beef and dairy combined), 25–26 million sheep, and approximately 850,000 farmed deer. These figures fluctuate annually. Beef + Lamb New Zealand Economic Service, “Compendium of New Zealand Farm Facts,” various years. https://beeflambnz.com/ — Also: Ministry for Primary Industries, Situation and Outlook for Primary Industries. https://www.mpi.govt.nz/↩︎

2. NZ livestock processing volumes: Stats NZ, Ministry for Primary Industries. NZ processes approximately 5–6 million cattle and 25–30 million sheep per year under normal conditions. Deer processing is approximately 400,000–600,000 per year. These figures reflect both domestic consumption and export processing. Under recovery conditions, total processing numbers will decline with reduced livestock numbers but the proportion of hides available for NZ use increases from partial (many exported) to total.↩︎

3. Tanning labour estimates: Based on traditional tannery practice. See: Waterer, J.W., “Leather and the Warrior,” Museum of Leathercraft, 1981. Also: Salaman, R.A., “Dictionary of Leather-Working Tools, c.1700–1950,” Allen & Unwin, 1986. The 2–4 person-hours per hide is for direct labour (fleshing, handling, finishing) and does not include the passive soaking time in lime or tan liquor, which requires periodic checking but not continuous attendance.↩︎

4. Cattle hide properties: Standard leather science. See: Covington, A.D., “Tanning Chemistry: The Science of Leather,” Royal Society of Chemistry, 2009. Cattle hide is the standard benchmark material for leather production — thicker, stronger, and more versatile than other common hides.↩︎

5. NZ livestock numbers: Stats NZ and Ministry for Primary Industries. As of the mid-2020s, NZ had approximately 3.8 million cattle (beef and dairy combined), 25–26 million sheep, and approximately 850,000 farmed deer. These figures fluctuate annually. Beef + Lamb New Zealand Economic Service, “Compendium of New Zealand Farm Facts,” various years. https://beeflambnz.com/ — Also: Ministry for Primary Industries, Situation and Outlook for Primary Industries. https://www.mpi.govt.nz/↩︎

6. Sheep skin properties: Sheep skins produce lighter, thinner leather than cattle hides. The distinction between “hides” (from larger animals — cattle, horse) and “skins” (from smaller animals — sheep, goat, deer) is standard terminology in the leather trade. See: Sharphouse, J.H., “Leather Technician’s Handbook,” Leather Producers’ Association, 1983.↩︎

7. NZ livestock processing volumes: Stats NZ, Ministry for Primary Industries. NZ processes approximately 5–6 million cattle and 25–30 million sheep per year under normal conditions. Deer processing is approximately 400,000–600,000 per year. These figures reflect both domestic consumption and export processing. Under recovery conditions, total processing numbers will decline with reduced livestock numbers but the proportion of hides available for NZ use increases from partial (many exported) to total.↩︎

8. Deer hide properties: Deer leather (buckskin) is historically prized for its combination of softness and strength. See: Richards, M., “Deerskins into Buckskins: How to Tan with Brains, Soap, or Eggs,” Backcountry Publishing, 2004. NZ’s farmed deer industry produces significant volumes of deer hides, mostly exported or underutilised under normal conditions.↩︎

9. NZ livestock numbers: Stats NZ and Ministry for Primary Industries. As of the mid-2020s, NZ had approximately 3.8 million cattle (beef and dairy combined), 25–26 million sheep, and approximately 850,000 farmed deer. These figures fluctuate annually. Beef + Lamb New Zealand Economic Service, “Compendium of New Zealand Farm Facts,” various years. https://beeflambnz.com/ — Also: Ministry for Primary Industries, Situation and Outlook for Primary Industries. https://www.mpi.govt.nz/↩︎

10. Hide preservation urgency: Bacterial decay of raw hides begins immediately post-mortem. The rate depends on temperature — faster in warm conditions, slower in cold. The 4–6 hour window for warm conditions is a standard tanning industry guideline. See: Thorstensen, T.C., “Practical Leather Technology,” Krieger Publishing, 1993.↩︎

11. Salt curing of hides: The standard preservation method worldwide. Salt concentration of 30–40% of hide weight is the industry standard for reliable preservation. See: Covington, 2009 (see [^4]). Also: UNIDO, “Introduction to the Leather Industry,” United Nations Industrial Development Organization, various years.↩︎

12. Air-drying hides: A viable preservation method in dry climates (East Africa, Central Asia) but less reliable in humid conditions. NZ’s maritime climate, particularly on the West Coast and in winter, makes air-drying less dependable than salt curing. Dried hides must be protected from rain, insects, and rodents during the drying process.↩︎

13. Beamhouse operations: The collective term for all hide preparation steps before tanning. See: Covington, 2009 (see [^4]). Also: Thorstensen, 1993 (see [^7]). The sequence and timing described here follows traditional practice adapted for NZ conditions.↩︎

14. Liming: Calcium hydroxide solution at 5–10% concentration, soak time 1–3 weeks. The pH of a saturated lime solution is approximately 12.4. Liming is the single most important preparation step — it determines hair loosening, hide swelling, and subsequent tannin penetration. See: Covington, 2009 (see [^4]).↩︎

15. Animal hair from dehairing: Cow hair, horse hair, and goat hair have long served as reinforcing fibers in lime plaster — the hair prevents cracking during drying and adds tensile strength. The same principle applies in brick manufacture. Animal hair was also a standard stuffing material for upholstered furniture and mattresses before synthetic foam. For plaster hair reinforcement, see: Ashurst, J. and Ashurst, N., “Practical Building Conservation: Stone Masonry,” English Heritage Technical Handbook, Vol. 1, Gower, 1988.↩︎

16. Deliming pH ranges: Vegetable tanning operates optimally at pH 3–6. The deliming step must bring the pH down from approximately 12 (liming) to this range. Vinegar (approximately 4–5% acetic acid) is an effective and NZ-producible deliming agent. See: Thorstensen, 1993 (see [^7]).↩︎

17. Traditional bating: Dung bating is documented in leather-making texts from antiquity through the 19th century. The active agents are proteolytic enzymes (trypsin, chymotrypsin) present in animal excrement, which partially digest non-structural proteins in the hide and produce a softer leather. Pigeon dung was historically preferred for its high enzyme content. See: Forbes, R.J., “Studies in Ancient Technology, Vol. V,” E.J. Brill, 1966. The practice is unpleasant but effective.↩︎

18. Vegetable tanning history: Vegetable tanning has been practiced for at least 5,000 years. Archaeological evidence from ancient Egypt, Mesopotamia, and China shows bark-tanned leather. The fundamental chemistry — tannin molecules cross-linking with collagen — was not understood until the 19th century, but the practice was refined empirically over millennia. See: Forbes, 1966 (see [^13]). Also: Covington, 2009 (see [^4]).↩︎

19. Black wattle tannin: Acacia mearnsii (black wattle) bark contains 35–45% extractable tannin on a dry weight basis, making it one of the richest tannin sources known. South Africa and Brazil are major commercial producers. Black wattle is widely naturalised in NZ, particularly in warmer regions (Northland, Waikato, Bay of Plenty, Hawke’s Bay). It is considered a pest species in some NZ ecosystems but its abundance makes it a valuable resource for tanning. See: Pizzi, A., “Tannin-based Adhesives,” in “Advanced Wood Adhesives Technology,” Marcel Dekker, 1994. Also: Roux, D.G. and Paulus, E., “Condensed Tannins,” in Harborne, J.B. (ed.), “The Flavonoids,” Chapman and Hall, 1975.↩︎

20. Tanekaha bark: Phyllocladus trichomanoides (tanekaha or celery pine) is a native NZ conifer. Its bark was traditionally used by Maori as a dyeing and tanning agent, producing a distinctive reddish-brown colour. Tannin content estimates are based on general reports of its traditional use rather than systematic chemical analysis — precise tannin concentration data for tanekaha bark is limited in the published literature and should be established through testing. See: Riley, M., “Maori Healing and Herbal,” Viking Sevenseas, 1994. Also: Te Ara — The Encyclopedia of New Zealand. https://teara.govt.nz/↩︎

21. Manuka tannin: Leptospermum scoparium bark contains condensed tannins. Manuka is one of the most common woody plants in NZ, covering millions of hectares of marginal land. Tannin content is moderate and variable. See: Hemmingson, J.A. and Wong, H., “Polyphenols of Leptospermum — bark tannins,” various NZ chemistry publications. Precise figures for NZ manuka bark tannin content should be verified through local testing.↩︎

22. Radiata pine bark tannin: Pinus radiata bark contains condensed tannins, typically at lower concentration than wattle or dedicated tannin species. However, NZ has approximately 1.7 million hectares of radiata pine plantation (Ministry for Primary Industries, National Exotic Forest Description), producing enormous volumes of bark as a sawmilling by-product. Even at modest tannin concentrations, the total available tannin from pine bark is substantial. See: Yazaki, Y. and Collins, P.J., “Pine Bark Tannins,” in Pizzi, A. (ed.), “Wood Adhesives: Chemistry and Technology,” Marcel Dekker, 1983.↩︎

23. Kanuka and native beech tannin content: Published tannin content data for NZ-grown kanuka (Kunzea ericoides) and native beech (Nothofagus spp.) bark is sparse in the scientific literature. Estimates here are based on botanical family relationships and general polyphenol chemistry — kanuka and manuka (both Myrtaceae) are chemically similar; Nothofagus bark tannins have been studied in Chilean species. All figures should be treated as provisional and verified through local extraction trials. See: Cadahía, E. et al., “Flavan-3-ol Composition of Bark from Nothofagus obliqua, N. alpina and N. betuloides,” Phytochemistry, 1997.↩︎

24. Kanuka and native beech tannin content: Published tannin content data for NZ-grown kanuka (Kunzea ericoides) and native beech (Nothofagus spp.) bark is sparse in the scientific literature. Estimates here are based on botanical family relationships and general polyphenol chemistry — kanuka and manuka (both Myrtaceae) are chemically similar; Nothofagus bark tannins have been studied in Chilean species. All figures should be treated as provisional and verified through local extraction trials. See: Cadahía, E. et al., “Flavan-3-ol Composition of Bark from Nothofagus obliqua, N. alpina and N. betuloides,” Phytochemistry, 1997.↩︎

25. Case-hardening: A common fault in vegetable tanning where the outer layers of the hide tan rapidly (sealing the surface) before tannin has penetrated to the interior. The result is leather with a tanned surface and an untanned core — weak and prone to failure. Prevented by starting with weak tan liquor and progressively increasing concentration. See: Covington, 2009 (see [^4]).↩︎

26. Pit tanning duration: Traditional pit tanning of heavy sole leather took 12–18 months for full penetration of thick cattle hide. Thinner hides and lighter leathers can be tanned in 4–8 weeks. Drum tanning (rotating the hides in a drum with tan liquor) reduces these times by 30–50% due to mechanical agitation improving liquor penetration. See: Sharphouse, 1983 (see [^5]).↩︎

27. Brain tanning: A traditional method practiced by Indigenous peoples worldwide, particularly extensively by North American Indigenous nations. The principle is that the phospholipids and fats in brain tissue coat the collagen fibers and prevent them from bonding to each other during drying. The folk saying that “every animal has enough brains to tan its own hide” is a rough heuristic from the brain-tanning tradition; it is plausible for deer and sheep hides but is not verified for heavy cattle hides where the mass ratio of brain-to-hide is less favourable. Practitioners report supplementing with brains from multiple animals when tanning thick hides. See: Richards, M., “Deerskins into Buckskins,” 2004 (see [^6]). Also: Edholm, S. and Wilder, T., “Wet-Scrape Braintanned Buckskin: A Practical Guide to Home Tanning and Use,” Paleotechnics, 2001.↩︎

28. Brain tanning: A traditional method practiced by Indigenous peoples worldwide, particularly extensively by North American Indigenous nations. The principle is that the phospholipids and fats in brain tissue coat the collagen fibers and prevent them from bonding to each other during drying. The folk saying that “every animal has enough brains to tan its own hide” is a rough heuristic from the brain-tanning tradition; it is plausible for deer and sheep hides but is not verified for heavy cattle hides where the mass ratio of brain-to-hide is less favourable. Practitioners report supplementing with brains from multiple animals when tanning thick hides. See: Richards, M., “Deerskins into Buckskins,” 2004 (see [^6]). Also: Edholm, S. and Wilder, T., “Wet-Scrape Braintanned Buckskin: A Practical Guide to Home Tanning and Use,” Paleotechnics, 2001.↩︎

29. Oil tanning (chamois process): True chamois leather was historically made from chamois (goat-antelope) skins, but the process works with any skin. Fish oil — particularly cod liver oil — is the traditional tanning agent. The oxidation of unsaturated fatty acids in the oil creates cross-links with the collagen. See: Covington, 2009 (see [^4]).↩︎

30. Chrome tanning dominance: Chrome tanning was developed in the 1850s–1880s and by the mid-20th century accounted for approximately 80–90% of global leather production. Its advantages — speed (hours vs. months), soft and flexible product, heat resistance — made it dominant. See: Covington, 2009 (see [^4]). Also: Thorstensen, 1993 (see [^7]).↩︎

31. NZ chromium deposits: NZ has no known significant chromite deposits. GNS Science / NZ Geological Survey mineral resource assessments do not identify chromium as a NZ mineral resource. All chromium compounds used in NZ are imported.↩︎

32. Alum tanning (tawing): Alum tawing produces a white, soft leather but the process is technically reversible — washing alum-tawed leather in water can remove the aluminium salts and return the material to a rawhide-like state. For this reason, it is not considered a true tanning process by leather chemists, though the product is functional for many applications. See: Covington, 2009 (see [^4]).↩︎

33. NZ alunite and kaolin deposits: Alunite occurs in NZ’s Taupo Volcanic Zone, associated with hydrothermal alteration zones. Kaolin deposits are found in Northland (derived from weathered greywacke and rhyolite) and in parts of the South Island. See: GNS Science, New Zealand Minerals and Mining (https://www.gns.cri.nz/). Also: Christie, A.B. and Brathwaite, R.L., “Mineral Commodity Report — Industrial Minerals,” Institute of Geological and Nuclear Sciences, 2003. The extractability and purity of these deposits for alum production has not been systematically assessed for industrial tanning purposes — this is a critical uncertainty requiring investigation during the asset census phase.↩︎

34. NZ alunite and kaolin deposits: Alunite occurs in NZ’s Taupo Volcanic Zone, associated with hydrothermal alteration zones. Kaolin deposits are found in Northland (derived from weathered greywacke and rhyolite) and in parts of the South Island. See: GNS Science, New Zealand Minerals and Mining (https://www.gns.cri.nz/). Also: Christie, A.B. and Brathwaite, R.L., “Mineral Commodity Report — Industrial Minerals,” Institute of Geological and Nuclear Sciences, 2003. The extractability and purity of these deposits for alum production has not been systematically assessed for industrial tanning purposes — this is a critical uncertainty requiring investigation during the asset census phase.↩︎

35. Alum tanning (tawing): Alum tawing produces a white, soft leather but the process is technically reversible — washing alum-tawed leather in water can remove the aluminium salts and return the material to a rawhide-like state. For this reason, it is not considered a true tanning process by leather chemists, though the product is functional for many applications. See: Covington, 2009 (see [^4]).↩︎

36. Leather drying: Improper drying — too fast, too hot, or in direct sun — causes surface hardening, internal cracking, and distortion. Slow, even drying in shade with good air circulation produces the best results. See: Sharphouse, 1983 (see [^5]).↩︎

37. Fat liquoring: The process of introducing oils and fats into the fiber structure of tanned leather to maintain flexibility. Without fat liquoring, vegetable-tanned leather dries hard and inflexible. The choice of fat affects the leather’s character — tallow produces a heavier feel than neatsfoot oil, which produces a lighter, more flexible result. See: Covington, 2009 (see [^4]).↩︎

38. Neatsfoot oil: Made by boiling the shin bones and feet of cattle in water and skimming the rendered oil. “Neat” is an archaic English word for cattle. Neatsfoot oil has been used as a leather conditioner for centuries and is considered one of the best natural leather oils — it penetrates deeply and maintains flexibility without darkening the leather excessively. See: Salaman, 1986 (see [^3]).↩︎

39. Currying as a distinct trade: Historically, tanning and currying were separate trades, often regulated separately by trade guilds. The tanner produced tanned but stiff leather; the currier transformed it into flexible, finished material. The physical working (staking) is the key step — it mechanically separates the collagen fibers that have bonded during tanning, restoring flexibility. See: Salaman, 1986 (see [^3]).↩︎

40. Iron liquor for black leather: Ferrous sulfate or iron acetate reacts with vegetable tannins to produce a blue-black or grey-black colour. This is the traditional method for producing black leather and was standard practice until synthetic black dyes became available. Iron acetate is easily made by soaking iron nails in vinegar. See: Covington, 2009 (see [^4]).↩︎

41. Tanekaha bark: Phyllocladus trichomanoides (tanekaha or celery pine) is a native NZ conifer. Its bark was traditionally used by Maori as a dyeing and tanning agent, producing a distinctive reddish-brown colour. Tannin content estimates are based on general reports of its traditional use rather than systematic chemical analysis — precise tannin concentration data for tanekaha bark is limited in the published literature and should be established through testing. See: Riley, M., “Maori Healing and Herbal,” Viking Sevenseas, 1994. Also: Te Ara — The Encyclopedia of New Zealand. https://teara.govt.nz/↩︎

42. Dubbin: A traditional waterproofing and conditioning compound for leather, made by melting tallow and beeswax together (typically 2:1 ratio by weight). Applied warm, it penetrates the leather surface and provides both water resistance and flexibility. NZ produces both tallow (abundantly, from meatworks) and beeswax (from beekeeping — NZ has a significant beekeeping industry, primarily for manuka honey production). See: any traditional leatherworking reference.↩︎

43. Harness leather requirements: A full set of heavy draught horse harness (collar, hames, traces, breeching, reins, bridle) uses approximately 5–8 square metres of leather of varying weights. Light driving harness uses less. Estimate based on harness-making references. See: Hasluck, P.N. (ed.), “Saddlery and Harness-Making,” Cassell & Co., 1904 (reprinted).↩︎

44. Industrial leather applications: Before synthetic materials, leather served numerous industrial functions. Leather drive belts powered by line shafts were standard in factories through the early 20th century. Leather pump washers, gaskets, and valve seats were used in water systems, steam engines, and hydraulic equipment. See: Salaman, 1986 (see [^3]).↩︎

45. Leather bookbinding durability: Leather-bound books have significantly longer service lives than paper-bound books under heavy-use conditions. Vegetable-tanned leather covers on codex bindings from the medieval period have survived centuries of use. For a Recovery Library document intended for decades of repeated reference, the durability advantage is material. See: Middleton, B.C., “A History of English Craft Bookbinding Technique,” Oak Knoll Press, 4th ed., 2000. Also: Roberts, M.T. and Etherington, D., “Bookbinding and the Conservation of Books: A Dictionary of Descriptive Terminology,” Library of Congress, 1982. Available at: https://cool.culturalheritage.org/don/dt/dt0.html↩︎

46. Rawhide: Untanned hide that has been cleaned, stretched, and dried. Extremely strong when dry but softens in water. Used historically for numerous applications where its shrink-on-drying property is advantageous. See: any historical material culture reference.↩︎

47. Tanning by-products: The leather industry historically produced several valuable by-products. Hide glue was a major product of leather scraps and offcuts. Hair was sold for plaster reinforcement and upholstery. Tallow from fleshing was rendered for soap and candle-making. See: Forbes, 1966 (see [^13]).↩︎

48. Hide glue: Made by boiling collagen-rich animal tissue (hide scraps, sinew, bone) in water. The dissolved collagen sets into a hard, brittle solid when dried, and can be re-dissolved by heating with water. Hide glue was the standard adhesive for woodworking, bookbinding, and many other applications before synthetic adhesives. Its advantages include reversibility (can be softened with water and heat for disassembly and repair) and strength. See: Horie, C.V., “Materials for Conservation,” Butterworth-Heinemann, 2010.↩︎

49. Vegetable-tanned vs. chrome-tanned upper leather — stiffness gap: Chrome tanning produces leather with a soft, draped hand immediately out of the tannery because chromium complexes bond to collagen in a way that prevents inter-fiber adhesion during drying. Vegetable-tanned leather, by contrast, dries with inter-fiber bonding that must be mechanically broken (by staking, stretching, and repeated bending) over time. Even after thorough fat liquoring and working, vegetable-tanned upper leather is typically stiffer than chrome-tanned equivalents and requires 2–6 weeks of use before conforming well to the foot. See: Covington, A.D., “Tanning Chemistry: The Science of Leather,” Royal Society of Chemistry, 2009 (see [^4]). Also: Sharphouse, J.H., “Leather Technician’s Handbook,” Leather Producers’ Association, 1983 (see [^5]).↩︎