Have heard about doing it, people use it to discover overspray etc. What am I looking for? How do I know if something has been altered? The more information the better, pics certainly appreciated.
that's a good thread on the subject. here's another:
from that thread, this makes it the most obvious:
"some were asking about pics from a blacklight test.
A bandmate has a guitar with a cracked and repaired headstock and today I tried to take some pics in a blacklight situation.
First a pic of the repaired area with normal light (neon):
I have a vintage (hihi) - Made in USA - Sylvania 47 inch long blacklight in my rehearsal room.
Today I switched the blacklight on, let it power up for some minutes, took the guitar on a stand, used a tripod for my camera, switched off the normal lights so it was totally dark and took the pic with 16 seconds of exposure.
Here's the result:
Well, the repaired area (the new finish) is clearly visible in the pic, the different hue/color is popping out. Hope this helped a bit."