A top-notch backglass restoration may bring a poor machine, destined for
parts, back to be a prized part of a collection. A very good article on how
to do this by Paul Midtdal and Barbara LeBlanc was published in the November
1990, Issue 26, of The Pinball Trader Newsletter.
The basic idea behind the technique is to use printers ink and the Pantone
color matching system. Part of the trick is dealing with opaque and
semi-transparent areas appropriately, and avoiding brush marks. The
article can be found at John's Jukes Website.