I keep getting obliterated by the painted trolls in the painted forest. I blow through the turpentine in no time with little effect. Do they have another weakness? Or is there another trick to killing them?
Your level shouldn't matter: According to the wiki, painted trolls are leveled, and have 25 HP per character level.
Trolls (including painted ones) do hate fire (50% weakness according to the wiki), so consider fire magicka or fire-enchanted weaponry if it's available.
Me, I just hacked them to pieces, blocking where necessary. Each of them is in his own area, so you should never get gang-mauled by them.
You can also consider sneak attacks, if you see them in advance and are a bow user.
Finally, they do have regeneration abilities.