About a year and a half ago, Todd Feinman at RAT told me about a period leather finish that could be made from one part melted beeswax and two parts linseed oil. The oil polymerizes so that the mixture isn't sticky when cured, and the beeswax keeps the mixture flexible.
Regular readers will recall that I've long been troubled by the question of how to reproduce the crenelated decorations frequently seen on Greek depictions of the gorytos. You could stitch on dyed leather or cloth, but that always struck me as needlessly laborious, and very difficult unless the case's main seam were opened up, so I've concentrated on finding a paint that will do the trick. It's my understanding that the gorytos and other such gear were made from soft, sueded leather cured with fat or oil, similar to braintan, so any paint would need to be water-resistant (as braintan-type leather soaks up water like a sponge and is hard to seal) and flexible so as not to flake off. It recently occurred to me that the beeswax-oil sealer might make a good paint binder for that purpose.
I tried it out by mixing a little melted sealer and red ochre (I didn't take measurements, but the amount of ochre wasn't enough to thicken the binder significantly), and when it cooled, rubbing it into a scrap of buckskin, scraping off the excess, and rubbing what was left in again. A few days later, when it felt dry, I cut the scrap in half and rubbed a top coat of unpigmented sealer onto one of the pieces. I also tried "priming" another scrap with sealer before painting it and adding a top coat, and rubbing/scraping/rubbing plain red ochre oil paint onto a third piece, which was also then given a top coat.
Yesterday I put all four pieces into a sink full of water and let them soak for an hour and a half. The result was impressive: None of the paint on any of the four pieces ran, smeared, or softened in water. They had apparently sealed in all the pigment in a good-as-waterproof manner. I even scraped the paints with my fingernail and none came off. The plain oil paint worked just as well when rubbed and scraped instead of merely brushed on, but it cured much stiffer than the beeswax-oil paint, so between the two, I think the beeswax is preferable. The additional top coat was not needed, though I suspect it would make the paint job more durable in the long run. Because German buckskin is so pale, only a little paint is needed.
This technique comes with a number of caveats:
1. I know of no evidence whatsoever that the Persians or anybody else actually used a paint like this in antiquity. The materials would've been available, but I have no reason to think that anyone combined them and used them in this manner, other than that it would've been a great way of making those crenelated bowcase decorations.
2. I used hardware-store boiled linseed oil. This version has some sort of chemical additives that cause it to cure faster than the kind that would've been available in our period, which (if used as a paint binder) would've been functionally equivalent to the purer linseed oil still sold in art stores for making traditional oil paint. In other words, if you use the more period-correct oil, you'll need to allow much more time for it to "dry." On the other hand, it's doubtlessly less toxic.
3. Many leatherworkers believe that linseed oil's chemical properties degrade leather fibers over time. However, I think the paint only soaks in shallowly, so I don't think it'll prove much of a problem.
4. The rubbing and scraping technique is useful only for producing large, simple designs. It may be possible to apply finer oil paint designs on leather that's been glued to a hard surface and primed with drying oil; if so, that technique might be appropriate for scabbard facings glued to a wood core.
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