Bark Tanning

Have any of you guys tried ponderosa pine bark for tanning. Am having some thinning done mechanically and I can go pick up bark stripped from the trees by the buckets full. I know it is not the best, but pretty limited around here..

Hemlock bark was what they used back in the late 18oos for the leather tannerys in central Ontario
Not sure how much tannin is in pine bark.

I felled a swamp white oak this spring. I am going to grind up the bark and use it for tanning squirrel before trying other pelts. Any suggestions?

Steven has an excellent article about tannin content of various barks.
Vegetable tanning materials........... Skill Cult