Although old stocks of photo paper have been found, most photo paper made after the war contains phosphates to artificially brighten the paper. Because it is the presnce of phosphates which makes an article (clothing, paper) react to blacklight by "glowing," many postwar forgeries can be detected in this way. However, forgers of photographs have become adept at giving the photographs "chemical baths" which leech out or neutralize much of the phosphate content, a treatment which is followed by other baths to yellow and age the image. It is still possible to tell, but one must have experience and knowledge -- and be cautious.