A limited form of chemistry on Tar seems to have been practiced.
Old discovery, I read about it easily greater than a decade ago - and I have used the lay a flat cupped stone under rolled up birch bark to catch drips and a sort of combustion chamber of leaned stones to keep direct coals and fire away from the bark. I had prevously knapped a knife blade and used it to set it into a bent wood handle. Wish I still had it, it was pretty crude, not the best blade ever made. [it got a winding of rawhide thong [I didn’t trust what I was told about how solid the blorp of tar would be]
I actually love the field of experimental archeology, as an historical reenactment wonk we do this crap in splendid isolation just to figure something out for ourselves =)