I found this but don't have a source of acorns to try it. https://bushcraftusa.com/forum/threads/tanning-hides-furs.20746/ "It is common knowledge that an animals brain is sufficiant to tan its own hide but few folks know about the use of acorns for the same purpose...No mess or bad smells... You prepair a hide as usual (I leave the fur on cause I use it for fly tying) and put it on the board fur side against the board... Gather the acorns and shell them... Grind up the acorn meats untill it is about like peanutbutter... Now that the acorns are prepaired,,,,,,,,,,,, (1) spread a layer of the acorn butter on the skin side of the hide... (2) when the acorn butter starts to crack and you see hide through the cracks go ahead and peel the acorn butter off the hide... (3) take the hide off the board and work it a little and put it back on the board... (4) you will have to do steps 1-3 2 or 3 times then your done... It works great and leaves the hide soft & pliable and no bad smell... Acorns has tannic acid in them and the darker colour yellow the acorns are, the stronger the tannic acid content is and thats why acorns are bitter tasting..."