the front panel’s paint and decal were very matte, and had signs of yellowing outside the decal. Everyone who has dealt with a Royal 5 (in particular) might know a case of this illness: the paint appears dirty and uneven with some yellow, grainy stuff around the decals. You cannot clean over decals too much: the golden color will go away to reveal silver, and eventually you will destroy the decals completely.But I had heard that that yellow stuff, on some machines at least, was shellac: that the decals were originally applied and then shellacked. For some reason, on the Royal 5 in particular, the shellac had a tendency over time to dry and become apparent and grainy.

Use kerosene or mineral spirits to clean the machine. I wouod go with kerosene to be honest. Then redo the shellac finish with french polishing. This is heavy documented with old sewing machines as they use these gold decals that f becomes silvered when water or cleaning solvents touch them.

I only used Turtle wax on the paint. You can go over the decals provided you don't polish and put too much pressure on them.The nickle was done with a generic metal polish.

Old school repair guys used a lot of different stuff that's no longer available due to being... Not good. Ha. But naphta was one that's still widely available as white gas aka "coleman/camping fuel" Essentially naphtha with stabilizers to keep it from going bad. Mineral spirits works as well, but naphtha leaves less residue in my experience. Lacquer thinner is good for especially stubborn crap and cleaning slugs, but evaporates really fast and the fumes are no bueno. Alternatively; non toxic degreasing cleaners like simple green are usually my preferred method of cleaning up especially gross machines. Typically very safe on paint finishes and internals, just make sure to keep it off the decals. (It can and WILL erase them if it sits for more than 10 secs) Really though, nothing beats air and a long handled "paint" brush. My air compressor and blow out tube are some of my most cherished tools.

Ultra One, a restoration firm whose specialty product is a de-rusting solution which is designed to remove only rust while leaving the underlying metal, paint and decals intact.