my friends dad likes to hunt and he makes his own long bows for hunting its actually really cool to watch how he makes them. it almost unbelievable how much work it takes.
I hunt too.........I've got 2 deer skins and 1 racoon in the freezer waiting to be doused with tannic acid. I use Oak bark for that process.........you might be shocked to know what is traditionally used to do the final tan.
The animals brain.....yep the brain. Any animal you want to tan, all is contained within to do the job as has been done for centuries. Sounds gross...no more than bleeding and gutting.