Are you tring to restore black FRN handles?. If so have you tried Mother's " Back to Black"?, its an automotive metal and plastic reconditioner that restores the black colour and sheen to faded and oxidized metal/plastic trim on autos. I've used this in my car craz days and it worked quite well, not sure about FRN though, but it is a form of plastic. Its a liquid which your supposed to rub into the part and then buff, you might want to use a old toothbrush to really get into the nooks and crevices of the scales textured grips. Might be a good idea to mask off the blade in case it could get stained. Let us know if this works.