I have done a couple of overlays with my printers help. Like some people have suggested the art after printing is cold laminated for protection. This custom Flash Gordon custom pin art is on its way to the USA. Along with masking for light lenses, Oracal 810 is what I have used for years so you can spray basecoat white after 2 coats varethane to sanded playfield. I would spray 2 - 4 coats varethane over white & level sand before installing overlay on wet application.

http://s36.photobucket.com/albums/e28/greatwichjohn/Ghostbusters%20overlay/