A blacklight is a great tool to use when inspecting antiques and collectables. It can detect repairs, flaws, cracks and paintovers. The blacklight will show restored or touched up areas on an antique painting. It can also be used to detect new vs. old paint on items. It is not 100%  fool proof and I have seen some new milk paints act like old paint, but it is quite accurate most of the time. New paint will show as dark areas on a painting, or it will glow a deep dark violet. Old milk paint on an antique piece will not glow deep voilet, it will be transparent or even change color. White will react with a bright purple, but old paint is more transparent. To get the hang of it, purchased a little hand held blacklight. (I purchased mine here on ebay). Test many of the items in your own collection: things that you know have new paint and those things that you are certain have old paint and compare the reactions. It works best in a dark room. When at shows and shops, carry your little light with you to check items before purchasing. You can see repaired cracks in pottery, stains on fabric-it is a whole new world viewing items with a black light!