Another use for oil
Require animal pelts
Instead of immediately curing the pelt for tanning
You would require the use of your skinning knife to carefully scrape the hide to make thin sheets. These sheets would be stretched within a frame and then cured. After curing, the sheets would be treated with acid and oils and the finished product would be vellum.
If anyone has ever seen the movies: Army of Drakness and Children Should Not Play With Dead Things. there is the item, Book of Flesh. Though fictitious, the Book of Flesh, was made from vellum using human skin. Eventually the book dires out, but becomes animated once it is dosed with blood. Morbid I know, but its cool.