1. Modern Leather Tanning: Cutting right to the chase, here are some of the synthetic chems used to tan the modern hide... chromium (VI or III), sodium sulphide, formaldehyde, glutaraldehyde, sulphuric acid, various solvents (which release volatile organic compounds), bactericides, paints, dyes, degreasers and surfactants. Reactions to chromium can cause such symptoms as gastroenteritis, shock, toxic nephritis, & perforation of nasal septum (really bad nose bleeds). That's some nasty stuff to wear against your skin - and luckily the EPA has some some standards (and oh, some exemptions) for the tanning process, problem is since the companies couldn't dump all the left over chromium & byproducts into the water and soil here they thought it was better to just move their facilities over to China, India, and other countries with less chem policies. Basically in summary these companies are assholes who really tan my hide by poisoning other people working for them, practicing animal cruelty and who want money more then the health of the planet - so don't buy into their toxic leather magic.
2. Vegetable Tanned Leather - I thought this type of leather was actually tanned with veggies (don't laugh...it might be dyed with some), but actually veg-tanning is a process which uses the "tannins" from the leaves and bark of trees (like the oak or chestnut tree). It is considered the "truest" form of leather tanning although is gives a stiffer less soft end product, that is also not as resistant to water damage. It may have the reigning crown of the "truest" but it does not mean the only natural or oldest way. Vegetable tanned leather is miles away from being as toxic as it's modern successor, but still needs to pass the cruelty check on how the animals were raised & killed - not all hunting practices are equal. Interestingly enough I wasn't able to find a good resource for buying this type of naturally tanned leather, except for bird toys. (This is because the slightest chem exposure can kill a bird and I am sure modern tanned leather as described in #1 would easily kill your pet tweety.)
3. Brain Tanning: If you are vegan, vegetarian or have a weak stomach this one might make you throw up a little in your mouth so read with caution! This method is extremely rare and is not used in industrial manufacturing practices, it is for the DIY leather maker who wants to actually use all the parts of the animal they hunt - creating a lower impact and far less waste then any other method. I recently learned about this type of tanning in a survivalist book from the library - here is a summary of what takes place: 1.Soak the hide in untreated water for two hours if you keep the hair and two days to remove it. 2. Stretch the hide. 3. Warm up the animal's brains on a small fire, while continually smooshing it up into a thick solution. 4. Rub the brains into the wet animal hide until it becomes soft (do both sides if there's no hair).
Gross much? I don't know, but even though this may make me gag in reality I think it is the most natural and innovative way to use the resources already available and would create the least toxic end product possible. Brain tanning is also least likely to be 'cruel' since it is not done in a manufacturing & slaughtering facility.
Note: Sometimes also called "oil tanning", industries claiming to use oil tanning methods are most likely veg tanning and then infusing the skins with oil to make it weather proof. They are not using the traditional oil tanning method from heating the animal brain.
What do you think about purchasing or creating of leather products? Do you find that modern leather smells too chemically?