Leather is nothing new and has been used since people first learned how to skin animals, presumably tens or hundreds of thousands of years ago. But the early types of leather that would have been used by what people know as cave men, would have been nothing more than dried skins.
After skinning the animal they would simply tie the skin on a rack and stretch it out, leaving it in the open for the air to dry it. This method worked but did nothing to preserve it in the long run, and also made the skins very tough and in need of lots of work before it was flexible enough to wear.
After the bronze age started people had the ability to make their own pots to boil things in and discovered that leather was much more effective when made in a certain way. Leather artifacts found from the Bronze age suggest how it was made, and it only takes 2 ingredients, animal skins and acorns.
The acorns were crushed and soaked in water to remove their high levels of tannin, which is a bitter oil like substance that the acorns produce. When crushed acorns are soaked in water the tannin leech’s out and turns the water a brownish yellow colour, this water is then added to a pot with some more water and heated to a boil.
( A leather stone age shoe over 10,000 years old, still good to wear-ish)
The skins are dried on a rack and then put in the tannin water and boiled for around an hour. The Tannin helps protect the leather against any kind of insect or bug that may eat it, and help to water proof the skin and massively slows down natural decomposition.
The only problem is that the leather becomes very tough, and this method was often used to produce leather armour. If the leather is to be used for clothing it has to worked after its dried, which is normally done by simply grabbing 2 handfuls of it and twisting it around to soften it up.