Cold-dyeing leather with madder root, part I

I plan on an all-new akinakes and scabbard for Plataea 2021.  My previous designs have used acrylic paints on the leather scabbard or leather facing.  Since I'm hoping to eliminate as much non-period materials as possible this time around, and I never figured out how to make a water-resistant paint for leather, my current aim is just to use a dyed red leather facing and maybe a bronze applique.

The trouble with dyeing leather is that the equivalent processes for fabric usually involve simmering them in water with mordants and dyes, but simmering leather invariably causes it to shrink and harden.  To work around that, I'm attempting both the mordanting and dyeing processes "cold" (which is to say, not hot enough to cause the leather's collagen protein fibers to coil up, which is what causes shrinkage and hardening).

Cold-mordanting is not unheard-of, as Sea Green and Sapphire describes.  Heat merely speeds up the process, but if you leave the fiber to soak overnight, you really only need enough heat to dissolve the mordants.  For me, all this is theoretical, and Heidi is speaking of wool, not leather, so we'll see whether it holds true in my situation.  It's my understanding that mordants for wool will work on leather, since both are proteins.

I'm using aluminum sulfate, which providence caused me to buy a pound of back when Allegheny Art was still operating in my town.  I have most of that left.  Ancient Mesopotamian records often mention alum and madder in association with leather, so we know this is a period-appropriate method.  Cream of tartar is, of course, readily available in grocery stores, and people should have at least been familiar with it in the Achaemenid period, since it readily precipitates out of fermenting grape wine.  Admittedly I don't know whether it was used to assist in mordanting at that time, but I'm willing to admit it as a plausibility.

The chamois leather in this attempt is from the nearby Ace Hardware.  It's also sold at Pep Boys, Home Depot, and probably other large auto supply and hardware stores.  Chamois, as I've noted before, is a type of fat-cured leather; the only difference between it and braintan is that the fish oil in chamois generates its own aldehydes as it oxidizes, so it doesn't need smoking to introduce them.  Thus, the fat is already permanently bound to the collagen, so wet chamois can be allowed to dry without kneading and will be easy to re-soften.

After cutting off some snippets for last year's casein paint experiment, I was left with 2.5 ounces of chamois.  Using the ratios from Botanical Colors, I came up with measurements of 14 grams of alum (just under a tablespoon) and 4 grams of cream of tartar (just under a teaspoon).  I dissolved both in Pyrex cups of hot water.  Interestingly the cream of tartar didn't seem to want to fully dissolve; around an eighth of a teaspoon of powder coalesced at the bottom of the cup no matter how many times I swirled it.

I dumped it all in a sink with warm tap water, added the chamois and kneaded it until it was thoroughly wet.  Tomorrow it gets hung out to dry, and with any luck we'll have some good weather ahead for the next stage.