134 ANNUAL OF SCIENTIFIC DISCOVERT. 



Becquerel's experiment, or under the sci*een of sulphate of qui- 

 nine, also referred to above. The plate is then ready to be i)laced 

 in the camera obscura, and to receive the colors of tlic spectrum, 

 or representations of nature, such as flowers, as well as ecirtain 

 colors produced by man. Lastly, he succeeds in increasing the 

 stability of the colors develojied on the sensitive surface by cov- 

 erino^ the jdate with an alcoholic solution of gum benzoin ; and 

 M. Niepce gives the name of Heliochromy to this branch of 

 photography. 



During his lengthened researches, ]\I. Ni6pce de Saint Victor 

 has made two series of observations, viz., that he can produce 

 with facility, on prepared plates, the binary colors of the spectrum, 

 viz., orange, violet, indigo, and green, if those colors are natural; 

 but, if they are artilieially i)n)duccd by the mixing of two of the 

 primary colors, as red and yellow, or orange and blue, or yellow 

 and blue, he cannot reproduce the binary- color, but only one of 

 the two colors employed by the artisan to j'rejiare them. Thus, 

 for example, he can reproduce the natiu'al green of malachite, and 

 the beautiful color known as Scheelc's green, but he cannot do so 

 with a mixture of Prussian blue and yellow chromate of lead, the 

 blue only reappearing. These facts enable him to exj^lain why, in 

 ordinary plii)t()grai)liy, the leaves of i)lants always appear l)lack, 

 and why, wlien iie attempts to fix on his i)lates the colors of leaves, 

 they have a bluish hue, the yellow portion of the color not being 

 reproducil)le. 



M. Niepce has made another series of observations which de- 

 serve notice, viz., that when a plate, as prepared b}- his process, 

 is dipped in an alcoholic solution of substances susce2)tible of im- 

 parting a color to flame, such, for example, as strontia, which eom- 

 luunicates a red hue to it, or baryta, which gives a yellowish-green 

 color, the prepared plates, when exi)osed in the camera, will as- 

 sume the same color as the salt which they have on their surface 

 would impart to the flame of alcohol; and, if a salt of copjKn- be 

 used, which has the property of comnumicating a vari(!ty of tints 

 to the flame of alcohol, the plate also will assume a variety of tints 

 when exposed to the action of light ; and during a certain period 

 of his lengthy researches, ]M. Niepce availed himself of this curious 

 jihenomi-non to obtain colored plates in the camera. — Dr. Calvert's 

 Cantor Lectures. 



ARTISTIC COLORING OF PHOTOGRAPHIC PORTRAITS. 



So difficult is the task of training a good colorist, that even the 

 accomplished aitist feels his inalnlity in endeavoring to impart the 

 information necessary to those he is wont to train in the knowledge 

 whereby he is enaljled to produce almost inimitable rijsults. 



Without attempting to go deeply into the philosophy of color, 

 analyticall^y or synthetically, it may not be out of place to give, 

 however slight, an idea of how to proceed in coloring a photo- 

 graph. 



It is indispensable that you Avash the proof well with a sj^onge ; 

 or, better, as ever at your command, sweep your tongue across it 

 in order to remo\ e any traces of grease or starch. 



