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1 ' The various modes heretofore adopted, to render impracti- 

 cable the copying ot notes by photography, are based upon 

 the use, in conjunction with black, of various colored inks, 

 and consist in printing, with one of those colors, a design on 

 the back of the note, or letters or figures on its face, or 

 finally in covering with colored lines the face of the note. 



" These plans are all ineffectual from the fact that the 

 colored inks may be effaced by chemical agents. I have 

 convinced myself by experiment that all the red and yellow 

 tints, hitherto proposed, may be destroyed without injury to 

 the paper, or to the ordinary black printing ink, which, 

 having a basis of carbon, is insoluble and indestructible. 

 The blue tints which have been employed are equally fugi- 

 tive, and besides, as this color reflects the chemical rays of 

 light, it is valueless as a protection against photographic 

 copying. 



" Another method has recently been introduced which 

 consists in covering the paper with a ground of red or yellow 

 color, and then upon the surface thus prepared printing the 

 note with a peculiar black ink of a nature so fugitive that it 

 is effaced by any attempt to remove by chemical agents the 

 colored ground. Fugitive black inks employed this way 

 offer a complete protection against photographic copying, but 

 they at the same time present great facilities for alteration 

 and render its detection difficult ; their use should therefore 

 be rejected. 



" The only effectual method free from objection is, in my 

 opinion, to be found in the use of a color which shall absorb 

 the chemical rays of light, and be like the black carbon ink, 

 indestructible and indifferent to all chemical agents. A note 

 printed with the ordinary black ink, and having its surface 

 previously tinted with lines of an ink prepared with such a 

 color, will be protected against the possibility of copying by 

 photography, by anastatic printing, lithographic transfer or 

 kindred processes, while it cannot be altered by any chemical 

 means. Such a color has hitherto been wanting, but is, in 

 my opinion, now supplied by the green ink recently patented 



