Michael Dresdner

straight talk about wood finishing

Spirit, yes; oil, no.

Q: Should I be able to remove 400 grit sanding scratches coming through on a French polished shellac coating by further polishing? Will an alcohol and mineral oil mix worked vigorously over the surface for a period of time eventually polish out these residual scratches or should go I back to 600 grit paper?
A: Certainly you are better off with 600 grit paper than 400 but there’s more to it than that. French polish eliminates scratches by dissolving the previous coat. You can do that with alcohol, which is a bit risky, but adding mineral oil will severely limit the ability of the alcohol to dissolve the shellac. Thus, it will make it much more difficult to remove scratches.
I’d suggest using French polish, a mixture of alcohol and shellac, and nothing else, to polish out the scratches. Once the scratches are gone, you can add mineral spirits to the shellac to make it more foolproof as a French polish if you must, but not mineral oil. Mineral oil and mineral spirits are very different; the latter is a solvent that will evaporate, while the former is an oil that will not.