142 ANNUAL OF SCIENTIFIC DISCOVERY. 



silver. The consecutive baths are to dissolve the non-adherent 

 silver precipitated over the whole'plate in each reinforcing bath, 

 while intensifying the fixed image. The washings in the reduc- 

 ing bath, rendering the metallic surface neutral, increase power- 

 fully the subsequent action of the reinforcing bath. The image is 

 now immersed for several hours in a bath of chloride or nitrate 

 of platinum, or in alternate baths of chloride of gold and nitrate 

 of platinum, or again in a bath of chloride of gold, according to 

 the color desired. During this steeping, the silver of the image 

 is partly replaced by platinum or gold, or a mixture of both. 

 The platinum bath gives eventually by vitrification a greenish 

 black, the alternation of platinum and gold yields black, and the 

 gold alone results in gilt images. Next the image is washed in a 

 solution of alkaline cyanide, or a concentrated solution of am- 

 monia ; then covered with a thick varnish of caoutchouc or gutta 

 percha, and heated in a muffle, when the organic matters are 

 consumed and the metal left. Finally, tlje image is covered with 

 a silicic or boracic glaze, and brought to an orange-red heat, by 

 which it is vitrified, and unchangeably fixed. Scientific American. 



PERMANENT PHOTOGRAPHS. 



At the last meeting of the members of the Inventors' Institute 

 (London), Mr. Pouncy, of Dorchester, read a paper on sun-paint- 

 ing in oil colors. The paper was illustrated with many fine speci- 

 mens of the applicability of his process to pictorial and decorative 

 art. The photographic prints exhibited were on paper, canvas, 

 panels, copper, etc., and showed a fine gradation of tone, quite as 

 perfect as the finest silver photographs, while it must be admitted 

 they possess over the latter the immense advantage of absolute 

 permanence. The sensitive medium used is bitumen of Judea, 

 dissolved in turpentine, benzole, or other hydro-carbon, with 

 which is ground up oil color of any desired tint. The pasty mass 

 is then brushed over a thin sheet of translucent paper, and dried 

 in the dark. When dry, the sheet is exposed under a photo- 

 graphic negative to daylight, or a strongly actinic artificial light, 

 which hardens or renders insoluble those parts of the sensitized 

 pigment to which the transparent parts of the negative have per- 

 mitted access of light. After some minutes' exposure to light, the 

 embryo picture is washed in turpentine, benzole, or any other 

 solvent of bitumen. This dissolves those portions which have not 

 been affected by the actinic rays, leaving the remainder of the 

 pigment firmly attached to the paper, in quantity proportional to 

 the amount of light which permeated the different parts of the 

 negative. The picture is now complete, and may be transferred, 

 as in the lithographic process, to card-board, wood, stone, etc. ; 

 or, if ceramic colors are used, it may be transferred to potters' 

 " biscuit," and burned in as usual. Mr. Pouncy may be con- 

 gratulated on having at last, after years of patient toil, so far per- 

 fected his process that it will now, in all probability, receive many 

 commercial and artistic applications. Mechanics' 1 Magazine. 



