This section is from the book "The Manufacture Of Boots And Shoes: Being A Modern Treatise Of All The Processes Of Making And Manufacturing Footgear", by F. Y. Golding. Also available from Amazon: The Manufacture Of Boots And Shoes.
The different ways of converting the pelt into leather may be generalized as tanning, tawing, and mineral tanned, or chroming. The former depends upon the astringent property of the bark and other vegetable products, which, when acting upon the pelt, transforms it into leather. Tawing is a preservative method of converting skin into leather. Tawed leather may be reduced to its former elements, whereas tanned leather cannot. Tanned leathers stretch less than tawed. Chromed leathers are produced by a soluble chrome soaked into the skin, which is precipitated by reduction on the fibre. Chrome productions are fast gaining popularity. It is superior in many of its qualities to tanned or tawed leather. It resists water and decay, it retains its strength, pliability, and softness under conditions that would destroy ordinary leather.