I see the same mistakes made over and over in tanning leather. This is the first in a planned series of video/blog posts on the most common of those mistakes in no particular order. I'll just make them when I have time and energy and happen to be doing something that I can shoot video footage of. See the tanning/leather/skinworking page of this site for all my tanning stuff.
I was recently preparing to put a skin into bark solution and thought it a good opportunity to talk about a common problem that home tanners run up against. Though the problem can manifest under varying circumstances, it is essentially that tanning solutions are not always given the opportunity to act evenly on the skin. One of the most common ways this problem manifests for home tanners is in using containers that are too small causing the skin to wad up in the bottom so that the solution can’t reach all the folds. Another common one is simply failing to stir and move the skin at appropriate intervals. Another, which I forgot entirely when shooting the video, is putting skins with dry spots into solution or failing to make sure the solution penetrates any dryish spots when it is first put in.
Why it’s a problem: Tanning is largely a process of various chemical actions on the skins. We may be soaking the skin in lime or ashes to de-hair it, soaking it in brains to saturate it with fatty acids for softening, soaking it in bating solution to soften it or soaking in a bark solution to tan it with tannic acid. In any case, the solution must simply be allowed to do it’s work by contacting the skin evenly.
Common Manifestations of This Problem
wadding skins up in small containers is a common mistake. this tub is large enough to tan this deer skin, but it still has to be moved around. A bucket could be used, but it is really too small and the problem would be multiplied. Home tanners just are not operating on a scale that allows for using really large containers, or constant movement as is possible with the large revolving drums used in tanneries, so we have to tend our skins at appropriate intervals.
One common way this problem manifests is when home tanners stuff skins into small containers. Small containers, like buckets, will cause the skin to wad up tightly in the bottom. Anywhere the skin is touching itself, the solution can’t reach it. This is like making tie-dye where the fabric is knotted and bunched together so the dye can only reach some parts of it and not others. That’s great if your a hippie, but not if you want an evenly tanned skin. Use containers that have a little bit of room so the skin can swim around in there some and not have as many places where it’s folded onto itself. You'll still have to move and tend the skin, but it will work better the larger the container is. As home tanners, we can't afford to use very large containers, because they require a lot more liquor, but there is a compromise such as the deer skin above stuffed into a tub. There is enough room to stir it pretty easily and it's not jammed in there as tight as it would be in the bottom of a bucket.
A skin stuffed into a tub of tanning liquor and left overnight. More time would not have improved this situation. The skin would have used up all the liqour and even if more were added, it would still not reach those folds unless the skin was stirred at intervals. This is not tie-dyeing. Tanning liquors must be allowed to act on the skin. A similar effect can happen in other solutions, but it's very obvious in this one.
Another common way into this problem is just not stirring or manipulating the skins. Unless you can get the skin completely spread out, there will be places that it is folded upon itself. In order to have every part of the skin being acted on by the solution at least most of the time, it must be stirred. How frequently depends on what kind of solution, but there is no situation I can think of where you can stir it too much. A particularly important time to stir is when putting skins into tannin solutions for the first time. I like to stir every hour or two for the first day to get the skin evenly colored. After that, more handling will make the skin tan faster, but the tanning slows down and the skin can be moved a lot less. Still, any other manipulations like removing the skin and draining it for a while, stretching it, more lengthy stirring and scraping over the flesh side of the skin, will ensure even action of a solution and in some cases cause the process to proceed more quickly. Just make sure when the skin goes back in that you stir it or stretch it enough to thoroughly re-soak it. For that matter, be sure that any time you put any skin into any solution, you are sure there are no dry spots and it is completely saturated.
Scraping over the flesh side of skins once or twice during tanning can really open up the fibers and allow for faster tanning.
There are very few times in tanning where skins were traditionally left for very long periods of time without any manipulation at all. In a process called “Handling” skins were often removed from solutions and then put back, often with a period of time resting out of the solution. At other times, skins were stirred, sometimes frequently, or even for hours at a time, or walked on in or out of the solution. Later, tanneries got large rotating drums, rockers to keep skins moving and pumps to keep solutions circulating to replace much of that manual labor.
This is a still I lifted from a cool video of an ancient Moroccan tannery that is probably still functioning just as it has for hundreds of years (or longer?). This worker is treading skins in a dye pit, but it could just as well be some other solution. We have the luxury of taking a little longer but in many cases the more the skin is moved, the faster the solution can work on the skin. In the case of dyeing like this it would also be necessary for even coloring.
It's hard to say what is going on here for sure. It looks like these guys are tanning or dyeing calf skins. They may just be moving the skins to a new solution, but piling skins like this to drain of their own weight for a while before replacing in solution is mentioned in the old tanning literature over and over again. If you watch any of these many videos of Moroccan tanneries, large piles of skins like this on the edges of the pits are a very common sight. It is likely that many of them are "handled" like this daily. In this scene, they are putting the hides into the pits and the worker in the pit is treading them down flat on the bottom. Simply laying skins away in there and leaving them would not effect the same result unless they are layered with quantities of crushed bark between each skin.
As a home tanner, you can get away with quite a bit of procrastination. For instance, I don’t handle my liming skins very much once they are well underway and that usually works out okay. I often don’t handle skins in bark solution as often as I should, but in the long run, it’s enough to get the job done. But most of us end up procrastinating way too much. Sometimes it works out, but often skins are damaged or incompletely processed. Solutions can also become weak and need bolstering, but that’s will have to be addressed specifically elsewhere. The take home message here is to keep it all moving
Keep the skin moving so that the places where it is folded over are constantly changed.
and...
Keep the solutions (especially tanning solutions like bark solution) moving through the skin by stirring and stretching if necessary, or by removing some of the liquid from the skin by scraping or draining before replacing it in the liquid.
Natural chemistry can do a lot of neat work for us, but only if the substances in our tanning solutions can reach the skin.
