174 HISTORY OF PHOTOGRAPHY. 



of color commouly called by florists the black rose, giyes a dark slate blue, as 

 do also the clove carnation and the black hollyhock ; a fine dark brown variety 

 of sparaxis give a dull olive green, and a beautiful rose-colored tulip a dirty 

 bluish-green ; but perhaps the most striking case of the kind is that of a 

 common sort of red popi»y (Paparer Rheum), whose expressed juice imparts 

 to paper a rich and most beautiful blue color, whose elegant i)roperties as a 

 photographic material will be further alluded to hereafter." 



This change of color is probably owing to different causes in different flowers. 

 In some it undoubtedly arises from the escape of carbonic acid, but this, as a 

 general cause for the change from red to blue, has, I am awai'e, been contro- 

 verted. In some (as is the case with the yellow ranunculi) it seems to arise 

 from a chemical alteration depending on absorption of oxygen ; and in others, 

 especially where the expressed juice coagulates on standing, to a loss of 

 vitality or disorganization of the molecules. The fresh petal of a single flower, 

 merely crushed by rubbing on dry paper and instantly dried, leaves a stain 

 much more nearly approximating to the original hue. This, for example, is 

 the only way in which the fine blue color of the common field veronica can be 

 imparted to paper. Its expressed juice, however quickly prepared, when laid 

 on with a brush, affords only a dirty neutral gray, and so of many others. But 

 in this way no even tint can be had, which is a first requisite to the experiments 

 now in question as well as to their application to photography. 



To secure this desirable evenness of tint the following manipulation will 

 generally be found successful : The pai)er should be moistened at the back by 

 sponging and blotting off. It should then be pinned on a board, the moist side 

 downward, so that two of its edges (suppose the right-hand and lower ones) 

 shall project a little beyond those of the board. The board being then inclined 

 twenty or thirty degrees to the horizon, the alcoholic tincture (mixed with a 

 very little water, if the petals themselves be not very juicy) is to be applied 

 with a brush in strokes from left to right, taking care not to go over the 

 edges which rest on the board, Init to pass clearly over those which project, 

 and observing also to carry the tint from below upward by quick sweeping 

 strokes, leaving no dry spaces l)etween them, but keeping up a continuity of 

 wet surface. When all is wet, cross them by another set of strokes from 

 above downward, so managing the brush as to leave no floating liquid on the 

 paper. It must then be dried as quickly as possible over a stove or in a cur- 

 rent of wai'm air, avoiding, however, such heat as may injure the tint. The 

 presence of alcohol prevents the solution of the gummy principle, which, when 

 present, gives a smeai-y surface ; but the evenness of tint given by this process 

 results chiefly from that singular intestine movement which always takes 

 place when alcohol is in the act of separation from water by evaporation a 

 movement which disperses knots and blots in the film of liquid with great 

 energy and spreads them over the surrounding surface. 



Corcliorus japonica. — The flowers of this common and hardy but highly orna- 

 mental plant are of a fine yellow, somewhat inclining to orange, and this is 

 also the color which the expressed juice imparts to paper. As the flower begins 

 to fade the petals irhiten, an indication of their photographic sensibility which 

 is amply verified on exposure of the stained paper to sunshine. I have hitherto 

 met with no vegetable color so sensitive. If the flowers be gathered in the 

 height of their season, paper so colored (which is of a very beautiful and even 

 yellow) begins to discolor in ten or twelve minutes in clear sunshine and in 



a A semicultivated variety was used having dark purple spots at the bases 

 of the petals. The common red popi^y of the chalk {Papavicr hybrid am) gives 

 a purple color much less sensitive and beautiful. 



