PHOTOGRAPHY BY ULTRAVIOLET AND INFRARED 601 



be shown by fluorescence photography. Examples are the removal of foxmg marks, 

 collectors' markings, names, dates, and invisible marks due to presence of saliva, milk, 

 soap, urine, etc. Papers themselves fluoresce differently in the ultraviolet, according 

 to the nature of the pulp, the sizing and other treatment of the paper, the age, and the 

 kind of pigment or dye added to color it. Paper deliberately stained or dyed to repre- 

 sent another in color may be detected by the ultraviolet if the dyes fluoresce differently. 

 Watermarks have been studied by the ultraviolet in order to distinguish between 

 genuine and false ones. Artificial watermarks produced by the application of an oil 

 or a wax generally fluoresce brightly. Others may be produced by impression with a 



Incas, Pa., January 23, 3 93P. 



This Is my will made this, day because 

 I am not well. I give all of my property of 

 all kinds to ray friend, Jacob C. 'Trustlg. 

 He is to settle my estate and can either sell , 

 the house or keep it as It is, I do this for 

 Jake because he Is my best friend and has done 



so much for me . 

 Signed. 



-<^^..y^?C.^^Seal, 



,."> Ifi&a's., Pa.,, January 25, 1932, 



A.C t t* ? /<^Sts 1-8 my will made this day because 

 ^I.ara Dofe well. I give all -of my croperty of 

 ^m- kiria& Vb-my' tT%bnd!, 'if|;^T^r'5ru^lg. 

 ^ ^ , ^He ^Is, Jt9 ,9etfcle /iiijr' estrfe-^jfe ancfe/jfta.,>ed^her sell 

 /, ' the house or' keep it as it is. I do this for 

 ^^ ^i^s -Aecs^jse^ 4ie?^*^<<Er<^t($w^i^e'nd and has done 

 so much for rae . 



/^ 



Signed. —f-^ary^yi e^ x 



^ ,'-^~yyvS><CJ^^^.^^^T<i Seal. 



Fig. 2. — Photographs showing detail which may be obtained through ultraviolet 

 photography. The top photograph shows a copy of a letter made with ordinary photo- 

 graphic methods. The bottom illustrations shoM's additional detail made "visible through 

 ultraviolet photography. 



rubber roller before the paper is dried. This renders parts of the paper thin by com- 

 pression, although the fibers are more densely packed in these parts. In a genuine 

 watermark the wet fibers are pushed aside, in making the paper, by the wire design, 

 so that the mark is actually thinner than the surrounding paper. Although it is not 

 possible to distinguish between these two types of watermark directly by fluorescent 

 photography, they can be identified after application of a sizing test solution which 

 consists of water or an oil containing a fluorescent material. The solution will pene- 

 trate a genuine watermark more quickly than the surrounding paper, so that it will 

 fluoresce before the paper. In an artificial watermark made by compression, the rates 

 of penetration are the same, so that the watermark will not be distinguished by 

 fluorescence. 



Postage stamps may be examined by the ultraviolet, and eradicated cancellations, 

 repairs to the paper, changes in the dye or pigment, or false watermarks detected. 

 Sealing wax varies markedly in its fluorescence according to its origin, color, age. and 

 the method of manufacture, so that fraudulent seals can often be detected, especially 



