I'm a painter so I have Turpenoid, and Turpenoid Natural (in the green can) in my studio. I have tried both on bike parts that were so crusty with black gunk that I thought they couldn't be saved. The Turpenoid, which is basically just odorless mineral spirits, did NOT cut the really nasty stuff, even when soaked in a jar for days and days. However, the Turpenoid Natural, which is a citrus-based solvent, completely removed all the fossilized black crap in a matter of an hour or so. I couldn't believe it. I used it straight, and soaked a chain in it that had at least a decade's worth of horrible black nastiness on it (this was on a used bike I bought and was trying to salvage). Soaked it, rinsed it in water, came out clean as a whistle. Turpenoid Natural is safer than Turpenoid, but you still NEED to wear gloves and work in a ventilated place. Always. And don't use any kind of mineral spirits like Turpenoid on your skin, it is absorbed into your system. The water based solvents like Turpenoid Natural, Pedro's, Simple Green, don't do this nearly as much and are much better for you and the earth. And they work.