Bark Tanning: Making the Bark Solution

Bark Tanning: page 4

Making the Bark Solution

Preparing the Bark

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

The finer the bark is ground up the faster and easier it is to extract the tannin (its a surface area thing). In the old days bark was crushed using a large stone wheel, much like a millstone, powered by an ox or horse. It was ground until it was the consistency of cracked corn, wheat berries, or a coarse powder. Modern folks use grain mills on a coarse setting, chipper/shredders used for making garden mulch, or they use their hatchet as best they can to pulverize the bark into small pieces. It should be emphasized though that the smaller you can get it, the more tannin you'll get from a given quantity of material. And as mentioned before, buying shredded bark (sold as garden mulch) is an easy and cheap way to go.
Leaching the Tannin

It is ideal to use rain or other soft water. Tanneries were traditionally located on rivers and streams because they used so much water. I don't know if they treated their water to remove minerals. The main reason soft water is preferred is because the minerals will react with the tannic acid and create spots or blemishes on the skin. So will blood, if any has been left in the hide (the iron in blood can react with the tannin to make a black stain). I don't know of any other functional reason to use soft water... the hide will tan without it.

Dark spots on surface of hide caused by using 'hard water' (water
containing minerals).

Tannin is water soluble. The warmer the water you soak the bark in the faster the tannin is extracted. Hot water darkens tannin resulting in a darker colored product. Boiling tannins especially darkens and dulls the color (like adding grays to it). Many sources recommend simmering the bark for several hours. Some traditions have you soak the bark in cold water for a few days to extract the tannin. This gives the lightest color. Your choice. Here are two recipes:
Lotta Rahme: "Fill kettle halfway with bark and totally full with water. Bring it to a boil and let it boil for at least an hour. Taste it. The more bitter and astringent the more tannin...like tea or coffee. Take half the liquor and mix with equal amounts of water for the first bath. Use a plastic or wooden tub."
Steven Edholm and Tamara Wilder: "Steven and Tamara use 1 to 3 gallons of shredded bark and soft water (rain or snow) to cover, in a 2-5 gallon stainless steel pot for several hours. Iron or aluminum pots will react with the tannic acid and cause stains etc., so don't use them. Plastic, wood, fiberglass, and masonry tubs are all suitable. Use wooden stirring paddles."
The First Bath

It is very important to use a very weak solution for your first bath. If the hide is put into a strong tannin bath, the outside gets tanned and shrinks. This inhibits the tannins from penetrating to the center of the hide, leaving the inner parts raw. This is called "dead tanning" or "case hardening".

Hides are start in a weak bath, and then
moved to progressively stronger solutions.

The first pouring is too strong so put this aside. Add more water, simmer again and pour off. Many tanners will put this aside too, and use the third extraction and then add up to three parts water to the one part liquor for the first solution.
The ideal bath to start with is one that has already been used for another hide. That way all the large tannin particles have already been used up. This is known as a "spent liquor". There is another advantage to spent liquors. In an old bark liquor, the bark sugars have fermented, forming lactic and acetic acid, which help remove any traces of lime as well as help preserve the hide.