Today we will talk a bit about greasy hides, specifically the leather underside of sheepskin. There are two main causes for greasy leather: improper cure and an older, fatty sheep. The former can be avoided, the latter cannot and may not become evident until the last stage of our process.
Driftless Tannery does not use chemical degreasers. Because we avoid using anything that is caustic, we rely on proper hide preservation. If the meat and, particularly the fat, is not removed completely from a hide during the curing process, the salt will only cure the fat and meat. The underlying fat tissue is left to bond to the skin. This can result in a less than perfect sheepskin.
The photo on the right, top, is an example of a hide that came off an animal that was older and fatty and the fat was not completely removed before salt curing, a double whammy. The dark spots are greasy to the touch. The yellow areas are left untanned. Tannin is unable to penetrate through the fat when bound to the skin.
Even the best prepared hide can turn out a little greasy if the animal itself is one that stores a lot of fat in the dermal layer (skin). From our experience, breeds such as Merino and California Reds tend to store a considerable amount of fat in their skin. The amount of fat stored in sheep’s skin increases with age.* The older the animal, the higher the risk of having a greasy hide.
The photo on the bottom, right, shows an example of an older, fatty sheepskin that was well cured. We have had some luck using cornstarch on these greasy hides. The cornstarch draws the fat up and we are able to then scrape it off. We have to repeat this process several times. This process can take hours, and the results are not as complete as we would like them to be. Oftentimes the grease eventually comes through the leather once again. It is near impossible to remove it completely.
As for the untanned, yellow spots in the top photo, there is nothing we can do to fix this issue. Again, proper hide preservation is the key to avoiding this type of finish. You can read about all the implications and the importance of proper preservation here.
Thanks, as always, for reading and for following our journey in natural tanning.
Team Driftless
*STUDIES ON THE THICKNESS AND CHEMICAL COMPOSITION OF THE SKIN OF SHEEP II-VARIATIONS DURING GROWTH By Manika Wodzicka at Ruakura Animal Research Station, Department of Agriculture, Hamilton (Received for publication, 11 March 1958)
