You can usually get the major auctions houses here and in London to black light most prints for you. Some varnishes or other surface treatments may also fluoresce, but with practice an experienced observer can tell the difference. These prints may actually glow in the dark even though they are vintage prints, because brighteners were added to papers very early-just not to commercially produced photographic papers. Some prints may have been made on hand-coated paper. Look for evidence of that treatment (tears, etc.). If there are spots or smudges of glowing areas, the image, which may be vintage, was probably washed/restored/treated in some way.
Oddly enough use of brighteners dipped substantially from 1965-1979, so care must still be used in dating many photographs. According to the conservator Paul Messier, only 1/3 of the prints he has so far tested from the late 1950s have brighteners and only 3% from the early 1950s his survey found peak use of the brighteners from 1960-64 and then post 1980, when papers made with brighteners made up 78% of the papers sampled so far. However, let us stress that should only be ONE indicator of date. If the photograph glows only in the baryta layer (the emulsion), then it may be one indication that it is very early to mid-1950s, because apparently that was where brighteners were added first. It used to be thought that the cut-off date was 1955-56, but recent evidence suggests that those dates given by manufacturers may have been the expiration dates of the paper instead of the creation dates, which are about two-three years earlier. If the print glows in the dark under black light, it was probably printed after 1950-51 (if on European paper) or 1953 (if on American paper) due to brighteners that were added to some photography paper starting around that date. This will help prevent damage from the black light to your eyes. While you are out shopping for your black light, remember to pick up a pair of ultraviolet (UV) plastic glasses. I bought my handheld one in Paris at such a shop. You can buy a decent one at Radio Shack for about $30, or a handheld one is available usually through stamp collector supply houses. A black light is just what it sounds like, one of those holdover fluorescent lamps from the 1960s psychedelic parties for those of you old enough to remember or those of you into ∦0s retro. One quick way to rule out many prints as being made more recently than 1951-52 is to use a black light.
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