I just want your opinion on these portable little black lights that are offered on E-Bay and About.com that claim to be able to see repairs, make-up's and fakes. Have you ever used them or will you consider using them?
I only study and collect porcelain and some pottery so my experience is limited to those materials, Personally I would not consider a black light as my first investment, but you certainly need one.
I personally have a very strong electric table UV-lamp that could lit up a whole room so to speak, when investigating ceramics. I find it in valuable in those cases. The only problem I can see, is that of an over-reliance on technology.
The use for a black light depends on you buying situation and what materials we are talking about.
Today's restoration can be very difficult to spot. Old times glue, plaster and paint will be detected at once with a black light, but then again so would it be even with your bare eyes. Modern epoxi-based restoration though, are not visible in UV light. Not even if whole chunks out of something are replaced, or big cracks are filled. Here you need your fingers and a loupe to check for glaze texture and bubbles, where almost only the absence of bubbles would tell you that the material is not porcelain.
A black light lamp can't detect fake ceramics. It can only lit up materials that somehow contains bleach, modern whitener and generally differences in reflection compared to its surrounding material.
Most often a magnifying glass and your nose might be quite enough to spot repairs, since some repaired pottery smell of plastic and glue.
Regarding porcelain, I believe that if you handle enough pieces you can feel the different touch of porcelain and paint. Most reveling - and even easier to feel - is the spray dust that often is all over the piece - except on the repaired area.
My way of checking pieces for damages is by just picking the piece up and turning it around a couple of times to feel if there is any "different" surfaces.
The repaired area could be smoother and "stickier" than the rest of the piece. Sometimes the pieces are spray lacquered all over, to avoid this to be detected.
At the slightest suspicion I hold whatever up against a strong lamp. At an outdoor market, the sun might do. At auctions and fairs, there is often a spotlight somewhere around. A strong pocket led light might come in handy. At least it will freak other viewers out and think you are a professional dealer, and leave your stuff alone. Or the other way around. They might bid extra high on things you look at since you seems to know your sh*t.
Anyway, with a strong light, then you can see the repair as a shaded area through the otherwise transparent porcelain. Even sprayed on paint will be visibly as a dark area.
The next thing I look for is hairlines. Really clean and new ones, that could have been made during the show, could be almost invisibly in soft light. Then you need a spotlight that can throw a beam of directed light along the surface. When this beam hits a hairline at a straight angle it becomes visibly.
If this is impossibly - the porcelain body could be too thick or the light might be to bad - I sometimes use a small needle or scalpel blade, and carefully slide over any area I suspect is repaired. This must be done very carefully so as not to ruin the repair if there is one. It is also generally a good idea to ask the seller for permission before you do this. If he says no, then you know the piece is repaired. Steel are softer than real porcelain glaze and should not damage porcelain glaze more than ordinary cutlery would do.
I mentioned this just because a black light - even if it does work - as with any tool might give you a false sense of security.
In order of importance, use your common sense, eyes, fingers, loupe, steel needle and - black light / UV lamp.
Thank you for your interest.