In the past, most leather was treated in a process called tanning, where the hide was exposed to wood tannin? which was of a low Ph, or acidic. This prevented normal decomposition and often inparted color.
Today, most leather is made of cow hides, but many exceptions exist. Some skins have during different times in history been considered very beautiful to make leather of. For these reasons certain snake?s and crocodile?s have been hunted to near extinction.