Bark Tanning: Soaking

Bark Tanning: page 5

Soaking

Contents
Intro & History
Tannins & Tannin Sources
Hide Preparation
Making the Bark Solution
Soaking
Currying
Softening & Finishing

As previously mentioned, you want to use wooden, plastic or masonry containers to do the soaking in. The bigger the container and the more solution that you have in it, the easier it is to evenly tan the hide. It is best to hang the hide(s) over sticks (crossbars) in the solution with as few folds and wrinkles as possible. If you don't, you should stir and re-adjust the hide more often.
Put the moist but drained skin in. Stir for the first 10 minutes and then once every 10 minutes for the first hour. Skin should be turned and agitated frequently in the first few days to assure even absorption. Epidermis will block the entry of tannin. If there are white patches it is from epidermis that was left. It must be scraped off, but be careful not to remove the grain. Lotta says that sheepskin epidermis is particularly difficult to get off.
Strengthening the Solution

You should use progressively stronger solutions. Different tanners recommend different timings for strengthening the bark solution. In general, you strengthen the liquor as you notice it looking weaker.
Lotta recommends strengthening it after the first several hours, removing the skin and membraning it again at this juncture. Mark Odle moves hides to the second run of liquor in a week or ten days. He then strengthens it weekly until the hide has been soaking for five or six weeks when the liquor can be used at full strength. One rule of thumb seems to be that you can push things faster if you are tanning thinner hides like deer and goat (which Lotta is), and that you need to be extra careful of case hardening with thick skins like cow, buffalo or bull elk.
After you start using full strength solutions, you can use the old bath to boil the new bark in, for added strength. However, bark liquor used as a first bath for skin that was de-haired with lime can contain residual lime and shouldn't be re-used. It should be thrown out. Once the whole skin has an even brown color, the bark can be left in with the skin, and you can leave it for longer times without stirring. If the hides stay in too weak a bath they begin to rot from the inside.
Mark Odle adds vinegar to further acidify and strengthen the solution. Mark adds three or four gallons to 80 or 100 gallons of liquor. Steven and Tamara used to this, but don't bother any more.

Smells, Molds & Textures

The solution should develop a somewhat pleasant fermented or vinegar like smell from the fermentation of the bark sugars. Smell can be strong but should never be putrid. A sulpherous smell indicates spoilage. At no time should the hide become slick, slippery or slimy. The texture will change from somewhat slippery to a firmer, textured grain. The pores and grain will become quite distinct. Mold may grow on the surface of the liquor, skim it off or stir it in. It is supposed to be (we haven't tried this) ok to freeze the skin in between baths.

Knowing When it is Tanned "Through"

Generally, to be considered 'through' tanned, the color should strike through to the center of the thickest part of the hide. To check this, snip a small piece off the neck. Lotta will also put a little saliva on the section that has been cut. Un-tanned skin will not absorb saliva easily and will appear wet, matted and glistening.

Another test is to fold the skin double two times and press the folded area between your fingers. When unfolded the fold should appear as light dry lines.

Some tanners say that the color should be even from the outer edge to the center. Doug Crist says he only has some color reach the center while the outer edges are much darker (much like the hide pictured above). However, he also says that softening the hide is a fair amount of work like brain tanning, whereas other folks say it should be much easier. This may be a factor of how much tannin you get into the center of the hide.

How Long

How long you soak your hide depends on the finished product that you desire. The longer you soak it the more it is "filled" with tannins. Once the color has penetrated to the center, you can either remove it from the solution and proceed to currying, or you can leave it in there longer to produce a 'fuller' leather. Getting color to the center of the hide means that some tanning has occurred throughout the hide. But you can always get more tannin to attach itself to the fibers and fill the spaces between the collagen chains. The amount of tannin can reach 50% of the weight of the finished leather.

The fuller the hide becomes, the thicker and less stretchy it gets. These are good qualities for saddles, belts and shoe soles, but may not be as desirable for other uses. Full-tanned hides are also easier to carve designs into the surface of. Contrary to this, one source says that thick hides used for sole-leather are sometimes left with an un-tanned stripe in the center which makes it more water tight and harder. This is also sometimes done for knife-sheaths.

Here are some ballpark figures of how long you should expect to soak your hides:

Mark Odle says deerskin sized hides should remain in a full strength ooze for three or four months in moderate temperatures. Cattle and buffalo will take five or six months. The warmer the temperature the faster the process. Once they are tanned through, there is no problem letting them sit in the bath as they will not rot. Looser fibered skins will take the tan more quickly than the tighter skins.

Lotta Rahme recommends as little as 7-10 days to tan a goatskin through, using around 1 3/4 to 2 1/4 lbs of dried bark. Goatskins are very thin. Cattle and elk, can take half a year or more.
A.B. Farnham: Harness and belting leather takes four 1/2 months (for cow), and 6 1/2 months for sole leather.