230 ANNUAL OF SCIENTIFIC DISCOVERY. 



portion of the glue with silver is added, and also mixed well, and allowed 

 about ten minutes' time for combining. Finally, the small portion of the 

 glue with the iodide is added, the whole mixture strained, and it is then 

 ready to be poured on the plates of glass or other suitable material. When 

 dry, the coated plate is ready for exposure. The photographic picture, the 

 drawing, print, or other subject to be copied, being laid on the prepared 

 coated surface, they are to be placed together in a photographic copying 

 frame, and exposed to the influence of the light. After a sufficient expo- 

 sure, which is exceedingly variable, according to the intensity of the light, 

 the plate is taken out from the copying frame, when it will be found to ex- 

 hibit a faint picture on the smooth surface of the sensitive coating. It is 

 then washed with water, or a solution of borax, or carbonate of soda, as 

 may be necessary. The whole image comes out in relief with all its details, 

 and, when properly done, with all its brilliancy. 



If the original is a photograph, chalk, sepia, or Indian ink drawing, the 

 copy represents the different tints in grains ; if in lines, the copy will repro- 

 duce the lines. 



When sufficiently developed, it must be washed with spirits of wine. 

 The surplus moisture is removed, and the plate is covered with a mixture 

 of copal varnish, diluted with spirits of turpentine. After some time, the 

 superfluous varnish must be removed by oil of turpentine, and the plate 

 treated again, or immersed in a very weak solution of tannin or other 

 astringent liquid. During this part of the process the plate must be care- 

 fully watched, and removed as soon as the picture or design is considered 

 sufficiently raised ; it is then washed in water and dried. In this state the 

 plate is ready to be copied. This may be effected by the customary methods 

 of rendering the coating conducting, and placing it in the electrotype appa- 

 ratus, producing an intaglio copper plate ; or, if first moulded, the intaglio 

 mouM furnishes the means of obtaining a relievo plate by electro-deposition 

 in a similar way. To produce a sunk design on the prepared plates, I pro- 

 ceed as before, but after washing with the spirits of wine, the plate must be 

 dried on a warm place, and in due time the picture or design will appear 

 sunk like an engraved plate. The printing plates arc produced as before 

 described. 



If an intaglio plate is made, it may be printed from, at the common cop- 

 per-plate printing press ; on the other hand, the relievo plate may either 

 serve as the matrix for producing an intaglio printing plate, or it may be 

 itself employed in " surface " printing, like a wood-cut. In the latter case, 

 the narrow lines of the impression being sufficiently raised, the broad white 

 spaces must be cut out on the printing plate, or built up in the matrix. 

 The common well known stereotype process also affords another means of 

 producing the necessary plate. 



PHOTOGRAPHS IN FACTITIOUS IVORY. 



An invention by Mr. J. E. Mayall, the well-known London photographer, 

 relates to the use of artificial ivory for receiving photographic pictures in- 



