Brain tanning hides is a very labor intensive process that uses an emulsified solution of animal brain and water to provide outstanding absorbancy to the final product. But at the end of the process the hide is exceptionally soft and unlike many leathers, is able to be washed. Nevertheless, the process of tanning hides by hand using the animal's brains, is not for the feint of heart.
At the end of a hunt there's often no time to tan the hide because attention has to be given to processing and preserving the meat. Native people used to tie the hides in a bundle and string it high up in a tree so that it was safe from scavengers. When the hides were removed from storage they are often dirty...and probably smelly. Nowadays after a hunt hides might be salted, rolled into a bundle and stored in a freezer until needed. For this discussion, I'll assume that no freezer is available.
When the time comes to begin the brain tanning process, the skins are first soaked in water to clean and soften them. Then, without doing damage to the rawhide itself, the skin is scoured to remove bits of flesh and fat. This first fleshing can be done over a wide log but eventually the hide must be stretched as wide and evenly as possible, usually on a frame made of poles but possibly between stakes pounded into the ground. The further the hide is stretched at this point, the larger the final piece of leather.
The point is to end up with a hide that doesn't have any holes or knicks, so any scraping is best done with a deer leg bone or a blunt iron flesher. The tanner's aim at this point is to remove every...EVERY... bit of flesh and fat, including the paper thin epidermal layer between the carcass and the outer hide.
What remains is fur on rawhide and this is left on the stretcher to dry taut.
At this point, instructions on brain tanning hides often jump into the preparatory steps leading to the final scraping of every hair and bit of flesh still remaining. But the next step really depends on what will eventually become of the hide. If the hide is intended to be made into a rug or warm winter coat only one side of the hide needs to be scraped, because the hair doesn't have to be removed. But if the intention is to make moccasins, a jacket or other piece of clothing, all the hair must be removed from the skin.
Some animal hides are better suited for one purpose than another. Deer and moose make useless rugs, but great footwear. Wolf and fox fur stand up to some abuse and are also good for embellishing clothes. Rabbit skins can be tanned but are either ornamental or cut into strips and knit or woven into a jacket or cape.
If the hair is to remain on the hide, it's unnecessary to follow through with any of the procedures that loosen the hair. But attention must be given to the application of the brain slurry so that its only carefully applied on one side.
If the hair is to be removed, then soaking the skin in a mild acid (urine was used in times past, for example), letting the skin putrefy for several months, or painting a sludge of slaked lime (wood ash and water or ground seashells boiled in water) will loosen the hairs. The hide should then be rinsed before proceding with the brain tanning.
Whether or not the procedure for loosening the hair has been used, at this point the rawhide, complete with fur, is soaked again in water and then thoroughly rung out so that it is just damp dry. A special wringer - one that holds the hide tight and allows the brain tanner to twist the skin until most of the water drips out - is often set up when many hides are available for tanning.
The hide must be damp to make it pliable enough to absorb the emolient...a mixture of brain and water, but if it is too wet, the emolient will be less effective. Nowadays tanners may wring the hide out between towels to easily absorb most of the moisture.
If its a large hide find someone to help twist it because soaked with water it might weigh 80 to 100 pounds.
Brain tanning is a messy job. The brain emolient is made by boiling the brain in an appropriate amount of water and then mashing it into a fine slurry. If the hair is to be removed, the slurry is rubbed thoroughly into both sides of the hide, rolled into a bundle, covered and left to sit for at least 24 hours. If the fur is not to be removed the brain slurry is carefully and thoroughly massaged into the back side of the hide and then the hide is stored for at least a day in such a way that no part of the brain mixture touches the hair.
After the oil from the brain permeates the hide it can either be soaked again in water, or not, but at this point the brain tanned hide is again stretched on a frame and the most tedious part of the process begins. Every inch of the hide must be scraped....and scraped....and scraped...and scraped again... until every hair and every bit of flesh and fat on both sides has disappeared.
Nobody has said that brain tanning is easy.
If the hide has been soaked the best tool to start with is a wooden wedge that is used over and over until no more water can be oozed from the hide. The second scraping tool can be a stick, between two and three inches in diameter, with one end carved into a smooth, blunt, rounded point.
When the scraping process is going on, intermittently the hide has to be removed from the frame and stretched in all directions. This can be done by one person by rigging up a device that allows the hide to be pulled over a rounded metal or bone 'blade' or even over a tree branch, but it's more fun to have a partner. The idea is to sit across from one another and pull the hide from the edges, rotate it and pull again. Rotate and pull, rotate and pull. Don't do any of this work in damp weather because the hide just won't dry out.
The scraping and stretching removes all moisture and permanently destroys the fibrous nature of the skin making it look somewhat like cream coloured heavy, thick felt.
The hide is finished but will become hard again if it gets wet. The way to prevent this is to hang it up over a smudge fire until the smoke entirely permeates the hide and changes the color to a nice brown. Traditionally, at this point the hides were loosely sewn into a cone shape and suspended over the smudge until the smoke color penetrated through to the other side, then the hide was turned inside out and smoked again until it reached the desired color.
Alternatively a small smoke house can be built - big enough to hang one or more hides so all parts are open to the smoke. Punky rotten wood works best for smoking but green wood can be used. The point is that different wood produces different colors. A nice golden brown can be produced from rotten spruce but the addition of a few cones will introduce a reddish tinge. A dark brown color emerges when the smoke comes from punky oak.