Acrylic Enamel
One of the most important things you can do when deciding to paint over enamel is to determine whether the enamel is acrylic. While it is perfectly acceptable to paint acrylic lacquer over other non-acrylic enamels, some types of acrylic enamels will not accept the additional coat. One easy way to tell if your enamel is acrylic is to apply a fine mist of methylated spirits to the surface of the enamel.
Using Lacquer of Acrylic Enamel
There is a type of acrylic enamel on which you are able to use acrylic lacquer: baked enamel. The baking process hardens the enamel paint thoroughly, so that an application of acrylic laquer will simply rest over the surface of the enamel. With air-dried acrylic enamels, the paint underneath the hard outer enamel surface remains soft and easily damaged by acrylic lacquer.
Using Acrylic Lacquer on Air-Dried Acrylic Enamel
If you use acrylic lacquer on any air-dried acrylic enamels, it will allow the lacquer to penetrate the hard outer surface of the enamel and enter the softer, unhardened paint beneath. This will cause the enamel to bubble, crack and craze, resulting in an uneven, damaged surface. The only way to treat such damage is to remove the lacquer and the enamel, or simply to start with another project.
How To Fix Damaged Enamel
If you have accidentally placed acrylic lacquer onto air-dried acrylic enamel, you may desire to simply start another project, as correcting the defects is a time-intensive activity. If you wish to continue with the same project, however, use either steel wool or a medium-grit sandpaper to even out any bubbles and cracks back to a smooth surface.