On a total repaint I have sanded the machine down to metal, or to the enamel paint that is original to it. Then prime it with auto primer, and spray with black enamel engine paint. Then apply decals. I have tried to spray shellac without success, so I now spray lacquer and it looks beautiful. I use an air compressor for the job of lacquer. I have on occasion then applied shellac as a top coat however this is VERY difficult to do with perfection, so I do not recommend it. Be sure that the paint cures at least a week before top coat. Some people have used automotive top coat but I do not...Good luck