There are numerous processes used in tanning hides, each providing different results.
One of the earliest methods utilized urine and feces dissolved in water in which the hides were soaked for varying periods of time. Then the hides were usually stretched on a frame and allowed to dry. The resulting leather is generally very firm and rigid. It can be soaked in water to allow forming into shapes that will be retained upon drying. This method was used to create body armor and shields that were capable of protecting against light weapons such as arrows or knives.
The above method remains in use in many parts of the world to this day, usually utilizing the waste of cattle, horses, or other domestic livestock. One of the earliest public recycling programs was in medeival towns having tanneries, with workers sent out to collect containers of "night soil" from individual dwellings.
Most commercial tanning today is done for the garment, upholstery, and shoe industries. Several processes are used, most based on metallic salts and commonly refered to as "chrome tanning". The resulting leather is generally soft and pliable.
The leathers most frequently used for holsters, belts, and pouches is created using the "vegetable tanning" method. Tannins are contained in many plants such as tea and many tree barks. Most vegetable tanning utilizes tree bark reduced to a powder form that will mix with water. Different trees have varying levels of tannins and can impart different results, primarily in color or shading of the hides. Raw hides are "fleshed", removing residual muscle, sinew, and other tissue, then soaked in a lye solution to remove the hair (which also bleaches the hides considerably). Then the hides are immersed in pits or vats containing a water with tannins in solution. Then the hides are stretched and dried, and frequently run through rollers under pressure for a generally uniform flat result. Hides will vary in thickness (refered to by weight in "ounces"), and can be split to uniform thicknesses via large cutting machines. The resulting leather is firm, can be wet-molded to shapes it will retain, and can be embossed, carved or tooled. Oak bark is highly regarded for tanning use, but others are also used regularly.
Native Americans and others used a "brain tanning" process with animal brains emulsified in water and used to soak the hides until fully cured. The resulting leathers are very soft, suitable for use in garments and footwear or other light duty uses. It is said that every animal's brain is sufficient to tan its own hide.
Vegetable-tanned leather can also be "retanned", run through a chrome tanning process after the vegetable tanning, creating very durable and pliable leathers for upholstery and other uses.
Vegetable-tanned leathers can also be "stuffed", which is a process of infusing the fibers with combinations of waxes and oils, creating very durable and pliable leather for uses such as harness and tack.
There are relatively few commercial tanneries remaining in North America, and those that remain are under heavy scrutiny by regulatory agencies. Historically, tannery sites have become heavily contaminated by pollutants including heavy metal residues, and a number of the "Superfund" clean-up sites have included tannery properties.
There are home tanning kits offered by several sources. I have not used them, but suspect that they are simple chrome-tanning processes.
Regular table salt can be used to cure hides. The result will be similar to "rawhide" that you may be familiar with from school or scouting projects. Very rigid and can be soaked in water to stretch and form into shapes that it will retain. Removal of the hair is most easily done with a lye solution.
Overall, tanning hides is a messy and nasty process that I would leave to those who have the facilities to do it in bulk lots. I would not want to have this going on around my house.
I'll just stick with vegetable-tanned cowhide from Hermann Oak Tannery and vegetable-tanned horsehide from Horween Tannery, fully processed and provided in the exact weights (thicknesses) I specify, and delivered to my shop ready to use.
Best regards.
