There are so many variables when it comes to naturally tanning. That is why I always say it is as much an art as it is a science. There is a lot of chemistry to understand in the tanning processes. There is biology to understand in the nature of an animal’s skin and fiber. Then there is the art of putting it all together and knowing what is happening and why it is happening.
The bark tanning process we at Driftless Tannery use is fairly forgiving in that if the skin is ready to accept the tannin, it will tan. We know it will take longer in a cold environment. We know movement makes the tanning process go faster. These are variables we can measure.
So how do we know the skin is ready to accept the tannin? We have learned that older skins, ones that may have been properly cured at the time of the animal’s death, tend to not want to rehydrate well. Any fat or meat that wasn’t removed before the hide was salt cured will hold firm to the dermis layer of the hide. If the hide was stored in an unconditioned space, like a barn or a garage, it will have been exposed to moisture, heat, and sometimes frozen temperatures over and over again. This will cause the hide to partially rehydrate and then dry out again. When this happens, the leftover meat and fat tends to bind to the dermis in such a way that the skin will never properly rehydrate again. In the case of really fatty hides, that fat layer is not stripped out in our process. In the chemical tanning world, they use degreasers to strip the fats away. We have yet to find a degreaser that we are comfortable with, one that is safe for our employees and safe for the environment. For now, we can only mechanically remove (physically scrape) as much fat as possible on a beam, with our fleshing knives.
Our wash process involves eco safe detergents and Dawn. We have tried other soaps, like many fiber enthusiasts know, Dawn dish soap is the best at removing lanolin and dirt from wool. We work each hide individually. We use a combination of soaking and wet brushing to remove the vegetation and debris. Sometimes we experience what we call “hair slippage”. This indicates to us that the hide was not properly cured or stored. Here comes the biology… Hair slippage is a result of bacteria action on the follicle of the fiber. When this occurs the fiber completely releases from the skin resulting in bald patches. Sometimes the hair rues or breaks. That can result from stress to the animal during life; fever, illness, parasite infestations, etc. There is also natural wool break that occurs in some of the older breeds of sheep. Identifying the cause for these occurrences help staff in a couple of ways. First off, as humans we tend to blame ourselves for what happens around us. It helps us to know the aforementioned causes of fiber loss on a hide. Secondly, we have learned how to treat each different case to save as much of the fiber as possible.
We work really hard to save every hide that is sent to us, no matter the condition. Sometimes no matter what we do, the fiber will break or fall out. Sometimes the leather will not tan evenly and there will be areas that are stiff or oily. It took a long time to realize that there are things that we cannot control on our end. The natural tanning process begins the day of harvest and lasts until our final finishing stages.
I created a little video on what happens to hides in our bark tanning process that are older or improperly cured.
As always, thank you for reading and for being a part of our community. Whether you are a farmer or an eco-conscious consumer, there would be no us without you.
Team Driftless