I always advocate starting from the least aggressive method and move up the line
to find what will be successful for the project.
I have used a single edged razorblade and slowly and meticulously start scraping
(not cutting – scraping) from the outside edge moving towards the center.
the blade should be fairly new and held about 90 degrees to the surface.
if that doesn’t work – try the wet-r-dry sandpaper glued firmly to a flat board
and with a slow trickle of water, sand softly until you start seeing the decal and
move to the rest of it.
hot solvents such as lacquer thinner, acetone and paint remover could potentially
remove the ink on the decal. Just the fumes of lacquer thinner in a small controlled container
will soften paint to the point it can be brushed off with a dry brush. (but so could the decal).