Well I was surprised, that's all. It says on the bottle that it removes copper (blue residue on patch), powder (black) and carbon (brown) - not sure I have ever noticed that distinction personally. Patches were coming out perfectly clean when I put it away and the dry patches to remove the excess oil came out clean too (apart from oil). The instructions say after 20 mins in the bore, patches will come out clean. Well I left 5-10 mins between patches and then left it in the bore for over 1/2 hour and then patches were still clean. Perhaps even after dry patches and oiling the stuff was still active in the bore? I don't know.