Loads Of Testing Yields New, Reliable, And Cheap Leather Hardening Technique

Leather hardening has been around for such a long time that one might think that there was little left to discover, but [Jason F. Timmermans] certainly showed that is not the case. Right around the end of 2018 he set up experiments to compare different techniques for hardening leather, and empirically determine the best options. After considerable effort, he crafted a new method with outstanding results. It’s part of his exhaustive testing of different techniques for hardening leather, including some novel ones. It was a considerable amount of work but [Jason] says that he gathered plenty of really useful information, which we’re delighted that he took the time to share it.

According to [Jason], the various methods of hardening can be separated into four groups:

  1. Thermal: heat-treating at 180 ºF or higher, usually via some kind of boiling or baking process.
  2. Chemical: soaking in a substance that causes changes in the leather. Some examples include ammonia, vinegar, acetone, brine, and alcohol.
  3. Mechanical: hammering the leather.
  4. “Stabilizing” methods: saturating the leather with a substance to add rigidity and strength without otherwise denaturing the leather itself. Examples include beeswax, pine pitch, stearic acid, and epoxy.

We recommend making the time to follow the link in the first paragraph and read the full results, but to summarize: heat-treating generally yields a strong but brittle product, and testing revealed stearic acid  — which resembles a kind of hard, dense wax at room temperature — was an early standout for overall great results. Stearic acid has many modern uses and while it was unclear from [Jason]’s reasearch exactly when in history it became commonplace, at least one source mentioned it as a candidate for hardening leather.

But the story doesn’t stop there. Unsatisfied with simply comparing existing methods, [Jason] put a lot of work into seeing if he could improve things. One idea he had was to combine thermal treatment with a stabilizer, and it had outstanding results. The winning combination (named X1 in his writeup) was to preheat the leather then immerse it in melted stearic acid, followed by bringing the temperature of the combination to 200 ºF for about a minute to heat treat the leather at the same time. [Jason]’s observation was that this method “[B]lew the rest out of the water. Cutting the sample to view the cross section was like carving wood. The leather is very rigid and strong.”

The world may not revolve around leather the way it used to, but there’s still stuff to learn and new things to discover. For example, modern tools can allow for novel takes on old techniques, like using 3D printing to create custom leather embossing jigs.

35 thoughts on “Loads Of Testing Yields New, Reliable, And Cheap Leather Hardening Technique

  1. Good data. The only major mistake that jumps out at me is that boiled leather was boiled in beeswax, but that also wasn’t the entirety of the hardening process – just a first step. Unfortunately, I haven’t been able to dig deeper into that particular thread of inquiry.

    1. While doing research, I found many different methods said to have been used historically. None involved boiling in beeswax. In fact I’m fairly sure that beeswax will smoke and burn long before it boils. Paraffin doesn’t boil until around 650F. Beeswax immersion was a common method which I tested and was not a top performer. I would be very thankful if you had a link for more reading about any historical hardening method that involved boiling beeswax.

      1. I’ve read that leather can be stabilized using hot beeswax or glue and that in this process, air bubbles are chased out of the leather, giving the impression of a boiling liquid. “Boiling leather” would in fact refer to “stabilizing”, and wouldn’t involve putting leather in boiling beeswax or water which, as you found out, does not yield the best results. Have you seen anything like that pseudo-boiling phenomenon during your experiments ?

    1. Who cares; good for 600-800 years ago but wont stop any modern projectiles. Think kevlar, uhwmpe combined with epoxy and silicon carbide etc will laugh at bodkin arrows. Congrats your are innovating in the 11th century.

        1. I’m thinking a knife or hatchet sheath would be great too. Normally I don’t super love leather sheaths because they tend to trap moisture and rust or stain the blade. If the leather is stabilized it might work a lot better.

      1. Yeah, it doesn’t matter how hard you make it you could never make car chassis from it or rockets to go to the moon either. Best to stop now and not waste any more time. :)

      2. You could say that about most articles here. But many articles, including this one, are still interesting even if there exist superior technologies. I’m glad that people take the time and effort and share the details. That’s what it’s about here I guess.

      3. What are you claiming? That because leather doesn’t work as armour it shouldn’t be investigated by those interested in it? There are plenty of uses for hardened leather, some uses where it excels compared to modern materials. Are you trolling, am I missing the joke, something else?

      4. I care. I applaud this research, which is hardly limited to the 11th century. The approach shown by this researcher is professional-grade. The classification of the hardening methods into four groups is excellent work itself. Building on this foundation allowed discovery of a much-improved technique. Leather is remains a desired product, worth a lot of money now and far into the future, in auotmobiles and fashion, for example. Furthermore, the principles discovered can be applied to other materials.

      5. Do not underestimate the amount of penetration that can be achieved by a properly designed arrow from a heavy modern bow. A standard arrow (without even trying) will go straight through soft body armour. Ceramic plates in plate carriers are a different matter, but I don’t think anybody has actually tried shooting a class IIIa plate. I can’t find a reference to anyone trying it in any case

  2. I’ve reported the useless, low-effort comments. I, personally, make motorcycle gear and tablet cases for myself out of leather and this is highly useful to me.

  3. I think leather is a great material that is so flexible in its uses but very undervalued. It is strong, flexible, it can be made to retain a specific shape, it can be made to be water resistant, and much more. There are many modern equivalents, but few can do everything leather can do and look good doing it. Thank you for the research and for sharing it with everyone [Jason F. Timmermans].

    1. Yeah. The problem is rather, where leather comes from and why it’s ultimately a bad idea even if you don’t care much about animal rights.

      Anything that comes as a byproduct of something else is tricky to use, because you can’t expand the supply arbitrarily without hitting huge marginal costs of production. That’s why leather tends to be a niche or luxury product. If everybody bought leather shoes and sofas and car seats, rather than bringing the prices down due to expansion and competition, the prices would go up because there wouldn’t be enough cows.

        1. I bet it’s like any other vegan product: either inferior in every way and not at all like the thing it’s supposed to replace, or already processed to the point of being useless except for one particular use.

          Like the meat substitutes that always replicate the end product, not the raw material, so you typically get some sort of “nuggets” that taste like desiccated bean-soup with breadcrumbs on top – and it costs three times as much as the real deal.

      1. Short term, yeah… the price will go up. I saw that during the “mad cow disease” incident. I used to run an online leather goods shop. I’ve actually used boiling water hardened leather for brackets in my tablet cases.

        But, a funny thing happened, as the price of beef and hides started going up, more ranchers started adding to their herds… and within 2 years prices started dropping again. Not to where it was BEFORE mad cow, but they’re nearly there now.

        That’s the beauty of the free market (even if it’s only partly free now…). If there’s a need, and the price is right, it WILL be filled.

        1. Growing cows just for the leather has large marginal costs because the price of meat and milk will drop due to overproduction, so the profit per cow can only rise to a certain point – beyond that, it’s uneconomical to increase production of leather unless the leather prices go up.

          If the demand for meat and milk goes up, then leather prices will keep coming down, but since cows fart so much methane and take up so much farmland and feed, they’re becoming a pricey proposition in general and I can’t see production increasing very much – rather, the market for cow meat will diminish and so will leather production.

  4. This is a very good piece of research in an area of craft and business where people are very conservative. I try to use chrome tanned leather when I can because it’s far cheaper than veg tan and I’ve had success hardening <2mm sheets with runny superglue.

  5. I guess that a similar technique can be applied to make fake leathers from mushroom mycelium. (Image) Search the net for “mushroom leather” and will get a lot of hits. These leather replacements are wonderful. So do not worry. The whole topic can even be seen from a vegetarian point of view. :-)

    1. That’s wild! In theory, you could make one solid piece of ‘leather’ that is 50m x 50m. You would just need a big enough vat. (I’m thinking that placing a mesh in the vat under where the scoby would grow would allow easy removal and support while it dried.)

  6. Hi all, Jason Timmermans here. Thank you so much for posting my research here. A lot of the concerns raised here are addressed in the article, and further armor testing was done using modern archery equipment. It did quite well, and I continue to develop the method. My site is onicrafts.com.

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