The process outlined by Dave Edson
is the same except:
Once the playfield is cleaned, support and level, with a level in both
directions. Buy the best brush on clear polyurethane available and finest
hair 3" to 4" wide brush. Make sure the work area is dust free as
possible. Carefully paint the entire playfield. Wait for a couple of days
before installing playfield pieces.
The finished playfield will shine like your never seen one before. I've
used this technique on 50 or so machines and the results are impressive.