Forms of leather

There are a large number of processes by which the skin of an animal can be produced into a flexible, strong material commonly called leather.

• Chrome-tanned leather is a more flexible and pliable leather than vegetable-tanned leather, tanned using chromium sulfate and other salts of chromium. It does not discolor or shrinks as significantly in water as vegetable-tanned. It is also known as wet-blue for its color resulting from the chromium
• Vegetable-tanned leather is flexible and brown in color which is tanned using tannin and other constituent found in tree bark, vegetable matter and other such sources. It is the lone form of leather appropriate for use in leather stamping or carving. This leather has a tendency to discolor while in water and shrinks when left to soak thus becoming less flexible and harder. It shrinks considerably in hot water, becoming stiff and ultimately brittle. In the past, it was seldom used as armor after hardening, and also it has been used for book binding.
• Aldehyde-tanned leather also known as wet-white leather due to its palm cream color is tanned using oxazolodine or glutaraldehyde compounds. It often found in shoes for infants and automobiles. Formaldehyde tanning (dangerous to workers) is another technique of aldehyde tanning. Brain-tanned and chamois leathers fall into this category and both are highly water absorbent . Brain tanned leathers are made by a manual process which uses emulsified oils, often those of animal brains. They are exceptionally soft and can be easily washed. Chamois leather uses oils (conventionally cod oil) that oxidize easily to form the aldehydes that tan the leather to make the fabric the color it is.
• Synthetic-tanned leather is white color leather, tanned using aromatic polymers like the Neradol or Neradol types. Melamine and other amino-functional resins also fall into this category providing the filling that modern leathers regularly require.
• Alum-tanned leather is tanned using by mixing aluminium salts with a variety of protein sources and binders, for example flour and egg yolk. Purist squabbles that alum-tanned leather is in principle "tawed" and not tanned, as the resultant material will decay in water. Extremely light shades of leather are obtained using this process, but the resultant material is not as flexible as vegetable-tanned leather.
• Rawhide, technically speaking is not leather, is made by scraping the skin thin followed by soaking it in lime, and then extending it while it dries. It is harder and more brittle than other type of leather, and is mostly found in uses where it does not need to bend considerably like drum heads, dog chews etc.