Mine was alum and salt mixed in water. Pelt sat in it for number of days. This was after scraping.
After that it was screwed down to plywood. Neats foot, ammonio, and water was rubbed in while still moist. Then hung/stetched by twine. As its drying you rub a baseball bat to stretch it. I had to trim the edges off.
Cool. I remembered more than i thought. Let me see if i can find the instructions/link.