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?
I found I could find specific spots standing on rocks in the area where I could shoot at them from range and they could not hit me. Finding one of those locations and using ranged attacks might be your best bet if you're having trouble.
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.