I am looking for a plug-in or brush that will cover a pattern with a clear gloss (glass) effect, without changing the underlying pattern

A good example would be lip gloss on a female.

Many thanks;

Ron H.

try the plastic wrap filter

Regarding this, I'm interested too, I've tried with the plastic wrap filter but if the lighting isn't right it doesn't really do much. Any tips or a way to control it and then try to add it on a separate layer?

some of the best samples i've seen of digital lip gloss were done by hand..there is a tutorial about making melted wax on worth1000.com that might be of benefit to you...