use, it was floated, back downwards, on a solution of bichromate of potash. When dry, it was exposed with the face in contact with the negative. The washing away of unaltered sensitive material and color was effected by cold or warm water, and a brush, to which sometimes a little ammonia, or acetic acid, was added. Mr. Blair describes this method as giving, with care, pretty good results.
The next step in carbon printing marks an important epoch in its history: we refer to the introduction by Mr. Swan of a prepared tissue for producing the pictures, which permits exposure on one side, and washing away on the other. This step, together, with the complete system of operations connected with its use, made carbon printing practicable as a useful art. The process was first announced in the Photographic News, early in 1864, and during many succeeding months continued to occupy a large share of public attention. The results were as perfect as the most fastidious could desire, and the process was so simple in itself, and so clearly stated by Mr. Swan, that for the first time in the history of carbon printing, many experimentalists gave attention to the subject, and produced excellent pictures. As the mode of working is given in another chapter, it is not necessary to state it here.
In the course of the discussions elicited in the photographic journals by the publication of Mr. Swan's process, we learn that Mr. Davies, of Edinburgh, had, in the course of experiments in photo-lithography, produced transferred carbon prints as early as 1862; allusion to which was made in a paper read at the Edinburgh Society in February, 1863. A series of circumstances, however, prevented the publication of his process until July, 1864. He then described a method analogous to that already patented by Mr. Swan, namely, coating paper with gelatine, bichromate, and pigment; exposure
