Sculptors seem to recommend Permalac, so I bought some. Have not used it much yet. I understand Nikolas also has good clear.

Krylon Clear also seems to work OK. Just be sure to get the glossy.

Run a test piece before you coat your real work.

It is all in the prep, so sand/polish until you are happy, then put on clean new rubber gloves without a powder coat, and use solvent to clean any oils. I spray immediately after I use the solvent, (allowing time for any residual solvent to evaporate).