Tanning Process
Introduction
This body of work examines historical hide processing, from raw skin to fleshing, salting, dehairing, grain removal, oil tanning, veg tanning, smoking, dyeing, and artifact creation. My research into historical tanning spanned thousands of years and multiple documented methods. Due to availability, I am using deerskin hides from a local butcher for my tanning samples.
Tanning is defined as a chemical treatment that converts raw animal skin into leather. There are three primary methods, oil (e.g. brains, organs, fish oil, egg yolks), vegetable (e.g. tree bark, sticks, leaves), and mineral (e.g. chrome, alum based) (9).
Of the three, two dominant methods emerged. Archeological finds from bogs and retreating glaciers found that during the late Stone Age, oil based fats, as opposed to vegetable tannins, were found in leather. This includes analysis on Otzi the iceman’s clothing, which did include deerskin (7,11), as well as Native American and Inuit leather processing (14). Iron Age bogs discoveries in Denmark show vegetable tannins detected in leather samples (11) and by the medieval period, bark tanning pits were found in major cities including Dublin (2). Tanner Guilds were granted by the King Henry II which shows how large and powerful the profession had grown (4). Methods not covered in this body of work include alum tanning, chrome tanning, or freeze tanning.
Different tanning and processing methods produce different results. Oil tanning produces soft, breathable, and flexible material, and when combined with smoke tanning, have increased resistance to moisture and resist decay. These align closely with prehistoric clothing, for example. Veg tanned (also called bark tan) rely on plant based tannins to alter the structure of the hide, producing a stronger, more rigid and water resistant material, such as belts, straps, scabbards, and armor (15).
I created a flowchart that organizes the phases of hide preparation into a structured decision tree for easy reference.
Flowchart
Hide Transformation Phases
Phase 1: Fleshing
After hides are received from a butcher, the first step in the tanning process is to “flesh” or remove excess muscle, fat and cartilage left over from skinning. If this step is not completed, like raw meat left on the counter, this excess material would quickly rot, and bacteria would destroy the hide. In addition, it ensures access to additional layers of the hide which need to be later removed, and in the end, ensures that tanning techniques get applied to the hide evenly. The Mappae Clavicula is a historical example where fleshing is described as process steps. It references the removal of tissue prior to treatment as part of parchment production, which is one end product of a leather hide (1).
Based on private instruction that I received from author, educator, and ancestral skills expert Woniya Thibeault, I built a fleshing beam out of a fallen tree. It was about 5 feet long, several feet in diameter, and already had its bark removed. I built a wooden “X” to raise the tree up off the ground, raising it to waist height. See figure 1 in Appendix for a picture of the fleshing beam.
Only two tools are effectively needed to complete the fleshing stage. The first is a fleshing knife (or “slicker”) a slightly curved, horizontal blade with two handles. The second is a small regular knife (like a pairing knife). The slicker is pictured in Figure 1340 in the book Craft, Industry and Everyday Life: Finds from Medieval York (6).
I learned through trial and error that if I used the knife to make a preliminary cut across the shoulders (beneath the neck) and worked down the spine, then excess muscle and fat would fall off easier. Once that entire section was completed, I could then turn it around and finish from the shoulders up through the neck. See Figure 2 for an example of what this looks like as I work my way down the spine.
The fleshing process is very time consuming, and the manual labor is intense. Each hide takes on average 1.5 hours to complete, not including breaks. Plus, the hides are heavy because they contain excess muscle, fat, and their “winter coat” is long and thick. The fleshing process requires you to pick up and adjust the hide on the fleshing bream multiple times per minute. I noticed that my recovery time between hides was anywhere from several hours to a full day. In fact, I injured my front right delt muscle after doing this same, repetitive motion for over 12 hours in the span of about 2 weeks.
After the hide is fleshed, action must be immediately taken, or the hide will start to decay. You must choose to either preserve the hide for a later date or jump to the tanning process.
Preservation (optional)
You may pause the process at this stage, but you must preserve the hide through freezing or salting to prevent decay.
Salting is a historically documented process that I completed to preserve the hides for future tanning. Salting was referenced in a 16th century customs and duties log, listing “Skins, Salted: Salted cow hides” as well as salted food (8). It was also referenced in a modern analysis of a medieval tannery in Kortrijk, Belgium. In the analysis, salt was found in tannery waste, and the leather “desalted if they were dry, salted hides” (13).
I had to learn how to salt through trial and error. I would lay the hide on a wooden board which had a slight angle. I would then apply ½ inch of salt across the entire hide. The salt would extract a small amount of extra “liquid” which would run off the hide since it’s on a slant. I would return the next day, wipe off the salt, and replace it with a new layer of salt. I would return the next day and examine the hide. If an area was stiff, cool, and blue, it was good. If it was warm, red, floppy, smelly, and wet, I would remove the wet salt from that area and replace with fresh salt. See figure 3 for a picture of my salted hides on a board. After the whole hide was stiff and blue, I would add one more layer of salt, fold it up, roll it, and place the hide in a bag or bin for future use.
When I’m are ready to continue the process, I rehydrate the hide by spraying and soaking it in cold water until it’s no longer stiff, paying close attention to folds and edges.
Phase 2: Dehairing and Scraping
Dehairing
Hair from an animal is effectively impossible to remove without assistance (I tried!). There are a few soaking methods to aid in hair removal: plain water, or “bucking” (14).
I soaked a hide in a bucket of plain water, indoors, at roughly room-temp for about 10 days, checking every day to see if I could easily pull the hair off with my fingers. The length of time depends on the temperature of the water. I was warned by Woniya, who lives in California, that during a hot summer, if the barrel is outside, the hide could be ready in as little as 24-48 hours.
A faster method, bucking, is a modern/North American term you may hear to describe a soak solution other than water. There are numerous historical sources that describe these solutions, the most common one being lime. The Mappae Clavicula, and On Diverse Arts include recipes/references of lime being used in the hide process, suggesting a widely known practice (1,3).
I prepared a lime solution with about 1 pound of hydrated lime and a large bucket half full of water, creating a milky white solution as described in the above-mentioned historical sources. I then soaked the hide for about 3 days, stirring and flipping the hide daily. Again, the amount of time will depend on the season and temperature of the water. Regardless of temperature, I check the hide twice a day by pulling on the hair to see how easily it comes off. See figure 4 of a picture of one of my hides in a lime solution.
When I was able to easily pull hair off the hide with my fingers, I removed the hide from the lime solution and carried it right to my fleshing beam.
Of course, removing hair is optional. You can oil tan or mineral tan a hide that has the hair on, depending on your end goal. If this is the case, you would skip this step entirely (14).
Scraping
There are multiple options when it comes to next steps, and they depend on what your end-goal is for the finished leather.
There are many layers on a hide and they get confusing quickly. Directly under the hair is the grain layer and this is one of the most important decisions. If your goal is a thicker, sturdier, and waterproof items (e.g. shoes, belts, sheaths, and armor), the grain will usually be left on. For items that require more movement, such as garments, gloves, shirts, leggings, the grain is removed. On the muscle side, there is a layer called the membrane, and this layer must be removed (14).
The hide is then laid on the angled fleshing beam hair side up. Using my fleshing knife, I made small, overlapping downward movements to push both the hair (and optionally) the grain layer off the hide. This also involves some serious manual labor. Each layer takes an additional 30-60 minutes of scraping. See Figure 5 for some stubborn grain layer that wouldn’t come off.
If bucking was used, the hide needs to be neutralized. A recipe from Woniya Thibeault included rinsing and soaking in multiple changes of clean water, and then using a mild acid, which is 1-2 tablespoons of white vinegar per gallon of water, for 30 minutes which will neutralize the hide.
After neutralization, water must be wringed out of the hide. If the hide is waterlogged, it will not absorb any of the tanning methods used in the next steps. Wringing is accomplished by wrapping the hide around a branch or beam multiple times, then sliding a strong pole or stick through, and twisting as hard as you can, expelling as much water as you can (14). See Figure 10 for an example of wringing.
End Goal
Hair
Grain Layer
Purpose
Hair on
Leave on
Leave on
Rugs, winter garments, trim, or when insulation is desired. Tanning=Oil or Mineral
Hair off, grain on
Remove
Leave on
Strong, stiff, bags, belts, straps, shoes, boots, armor. Tanning=veg
Hair off, Grain off
Remove
Remove
Soft, flexible, garments, pouches, gloves, gussets, or lining. Tanning=oil
Phase 3: Tanning
Oil (Brain Tanning)
If I’m oil-based tanning, I placed a hide in a mix of egg yolks and warm water. Egg yolks can be used in place of deer brains or other fatty organs. The number of eggs depends on the size of the hide, 6-8 for small, 10-12 for large, plus 1-2 cups of warm water. The brains/eggs contain fats and lecithin which allow the fibers to soften, “facilitating interaction between oils and collagen” (15). I usually let the hide soak in the solution overnight. It is interesting to note that oil based tanning is not a true “tanning” method because it does not chemically alter the structure of the hide (14).
After removing the hide, I will take it back to my spot and wring it again, removing as much liquid as possible.
After wringing, the hide must stay in motion until it is completely dry. This is called “softening.” If it dries wet, it will stiffen. I usually take the hide and “drag” it back and forth over a smooth, angled surface, like a rope or 2x4, or another object I may find in my yard. This repetitive motion is another manual labor intense activity and can be quite time consuming, typically 30+ minutes of softening. Instead of breaks, typically changing the angle to give my muscles a rest, instead of completely stopping. Please see Figure 9 for an example of me using the back of my axe throwing target to soften a hide.
This whole process should be repeated one more time, or until fully soft.
After softening is complete, a smoking truly tans the hide. Smoking the hide creates a “water-repellent leather using non-toxic methods, including brain tanning followed by smoke tanning, dating back to at least 5000 years to Otzi the iceman” (15). The smoke reacts with the collagen, creating a binding effect (14) (15). If a hide is not smoked, it will be vulnerable to bacteria, will smell, and will absorb water and stiffen.
Since we are talking about smoke from a fire, any creative combination of modern or ancient techniques could be used. But either way, a station should be setup where 1) a hot fire is started and is burned down to coal (no flames), 2) rotted dry wood or damp straw is placed atop the hot coals, creating excess smoke, 3) the leather is hung over the fire so as much smoke passes through the leather as possible (14). During winter months, for example, with frozen ground and snow, an outdoor wood stove could be lit, and the hide suspended above the pipe, allowing for smoke to pass through. I setup a tripod made out of three thin trees, positioned it over the fire, and hung the hide from it. Be careful not to let anything that conducts heat hold or mount the hide, such as a metal clothes hanger or any metal wire. You will sear the hide, and your hand! I use a wooden stick and deerskin thong when possible to mount the hide over the smoke. You will know when the hide is complete when it turns a nice yellow-brown color. Then flip the hide around and do the other side.
Veg Tan (Bark Tan)
The phrase “veg tan” to me is a bit of a misnomer, as “vegetables” are not used to tan a hide, but rather plant tannins that are found in certain organic matter. Tree bark is the most common and preferable (e.g. oak, hemlock), but other organic matter could be used, like twigs, leaves, hulks, or things like coffee grinds (14).
To prepare the bark liquor, I harvested hemlock bark from a recently fallen tree. The bark was removed with an axe, reduced into smaller pieces, and then simmered in water to extract the tannins (see Figure 6). The mixture was allowed to sit overnight to deepen the extraction. I decided to make sure it worked by soaking a strip of white paper, which demonstrated successful extraction (see Figure 7).
The hide is then submerged in the bark liquor where it undergoes a slow chemical transformation as plant tannins penetrate and stabilize the collagen structure. This stage may last weeks to months, often requiring changing out the liquor for a fresh batch. This extended time and close management of the liquor are among the reasons this ancient method is seldom used today.
To increase completion time, the bark liquor should be refreshed often. I noticed that the liquor gets cloudy and starts to thin, which is a sign that it’s time to change out the liquid for a fresh batch. Please see figure 8 that shows a test piece that’s been in 1 batch of liquor for about a week. You’ll know the piece it done when it feels more like wet leather than wet skin. You can also cut a small test piece and see if the color has penetrated all the way through.
Phase 4: Dyeing and Pouch creation
Dyeing
Using walnut hulls is a historically documented method for dyeing. The MFA Boston has a page with a description, recipe, resources, and citations. The MFA recipe says to grind the shells and “soak for two days, then boiled for 30 minutes” (18). Additionally, the Innsbruck Manuscript from 1330 Germany lists “The Nutshells, most likely Black Walnut, which produce a dark brown color” (5).
I collect black walnut hulls in the autumn months. Collection must occur soon after they fall because wildlife (especially squirrels) will take them. And you must store them in a very strong, safe location! Through experimentation, I learned the hulls cannot be stored at room temp. I had both an entire liquid batch and stored hulls turn moldy. That batch had to be discarded. Only when fresh hulls that were frozen or completely dried out were okay to use.
I got different results based on tanning method. Since a veg tan is tanned with tannins, using more tannins from black walnuts does not make a huge change. Because oil and smoke do not use tannins, the black walnuts have a more darkening effect. All types of leather including commercial cowhide that’s veg tanned, and chrome tanned deerskin have different and sometimes unpredictable color changes, and I recommend small test pieces.
Pouch
I prepared an elevation gift for Master Wilhelm in the form of a kidney (girdle) pouch. The design is inspired by archaeological finds published in Purses in Pieces. Surviving period pouches were commonly constructed from cowhide and goatskin with the grain layer (16).
Master Wilhelm’s pouch was made from an array of leather from my personal collection including veg tan cowhide, brain tanned deerskin, and other pieces of tanned deerskin. For the outer pieces, veg tan with grain on was chosen, and soft deerskin with grain off chosen for the gussets, pouchlets, and thongs. Every piece of the pouch (except for the thong) was dyed with my black walnut dye. No needle or thread was used during construction. A leather thong was used to sew the pouch and the two pouchlets together, which I replicated from figure 6 and 9 in Purses in Pieces (16). I used two different stitches, the saddle stitch (modern term), which is also described as a “double running stitch” and was found at the Coppenhagen site, as can be seen on figure 1590 in the book Leather and Leatherworking in Anglo-Scandinavian in Medieval York (17). I always used the “French twist” stitch that I learned from pervious leather project. See Figure 11 and 12 for progress pictures of girdle pouch.
Tooling, when a design “is impressed onto the surface of damp leather using a blunt point” (17) was used to create Master Wilhelm’s device on the front flap. His device depicts two horses, as he is a farrier by trade. I decided not to make a buckle strap as they are only “found on about 1 in 15 purses” (16).
Conclusion
This body of work shows that traditional leather processing is not one single craft but a distinct set of multiple skillsets. I have confirmed through personal recreation and research that tanning method, rather than animal species, typically determines most functional characteristics of the finished leather. From Paleolithic camps to medieval cities, leather was and remains a critical part of human material culture, from clothing, to armor, containers, bookbinding, belts, shoes, straps, harnesses, bags, and countless everyday objects.
Bibliography
1. Mappae Clavicula (9th c.) parchment recipe with liming + stretching/scraping. Discussed in: Degano, Ilaria, et al. “Revealing the Composition of Medieval Parchments through Non-Invasive Analysis.” Heritage Science 13 (2025).
https://www.nature.com/articles/s40494-025-02042-w
2. Giacometti, A. (2004) Dublin: 48 New Street South, Dublin Archaeological excavation report entry. https://excavations.ie/report/2004/Dublin/0011689/
3. Theophilus, De diversis artibus / On Divers Arts (early 12th c.)
https://archive.org/details/ondiversartstrea00theo
4. Halsall, P. (1998, October). Medieval Sourcebook: Henry II of England: Grant of a gild to the tanners of Rouen, 1170. Internet History Sourcebooks Project. https://sourcebooks.fordham.edu/source/1170rouentannersgild.asp
5. Leed, D. (2008). Dye Recipes from the Innsbruck Manuscript (c. 1330). In Dye Recipes from the Innsbruck Manuscript [Translation and commentary]. Scribd. https://www.scribd.com/document/462012129/Dye-Recipies-From-the-Innsbruck-Manuscript
6. Ottaway, Patrick, and Nicola Rogers. Craft, Industry and Everyday Life: Finds from Medieval York. York Archaeological Trust, 2002. https://www.collections.yorkarchaeologicaltrust.co.uk/files/original/74504/GB2837-PUB-AY-17-15-Medieval-Finds-from-York_P-Ottaway-N-Rogers.pdf
7. Deleted
8. Jones, Evan T. Bristol “Particular” Accounts / Port Books of the Sixteenth Century (UK Data Service Study Number 6275). Study documentation (PDF). UK Data Service. https://doc.ukdataservice.ac.uk/doc/6275/mrdoc/pdf/guide.pdf
9. Encyclopaedia Britannica, Inc. (n.d.). Tanning. In Encyclopaedia Britannica. Retrieved February 18, 2026, from https://www.britannica.com/technology/tanning
10. Deleted
11. Püntener, A. G., & Moss, S. (2010). Ötzi, the Iceman and his leather clothes. Chimia International Journal for Chemistry. https://www.chimia.ch/chimia/article/view/2010_315/4144
12. Larsen, R., Schmidt, A. L., Mortensen, M. N., Shashoua, Y., Sommer, D. V. P., & Richter, J. (2024). Iron Age fur skin tanning – a sustainable practice? Danish Journal of Archaeology. https://doi.org/10.7146/dja.v13i1.141323
13. Demiddele, Hendrik. “The discovery of a medieval tannery in Kortrijk.” PDF (ResearchGate). Discusses stages of tanning and notes hides “desalted if they were dry, salted hides” during preparation. https://www.researchgate.net/profile/Hendrik-Demiddele-2/publication/388593193_The_discovery_of_a_medieval_tannery_in_Kortrijk_by_Hendrik_Demiddelepdf/
14. Woniya Dawn Thibeault, private instruction in ancestral hide tanning and leather processing, 2023–present.
15. C. Covington (et al.), “Tanning,” in Tanning Chemistry: The Science of Leather (RSC, 2019) https://pubs.rsc.org/en/content/articlehtml/2022/va/d2va00050d
16. Goubitz, O. (2007). Purses in pieces: Archaeological finds of late medieval and 16th-century leather purses, pouches, bags and cases in the Netherlands. Stichting Promotie Archeologie. https://www.archers-du-bailli.be/costume/documents/cos-escarcelles/Purses%20in%20Pieces-ENG.pdf
17. R. A. Hall Leather and Leatherworking in Anglo-Scandinavian in Medieval York-Tooling and Incising
18. Museum of Fine Arts, Boston (CAMEO). “Black walnut dye (Juglans nigra).” https://cameo.mfa.org/wiki/Black_walnut_dye