In this process the material employed consists of a layer of gelatin containing carbon, or some other permanent pigment spread on paper.

In this condition the paper is not sensitive to light, but if it be treated with a solution of bichromate of potash, dried in the dark, and afterwards exposed to sunlight under a negative, those portions of the paper which have been acted upon by the light, will become insoluble, whilst those parts that have been protected from it, will be soluble. When, therefore, after sufficient exposure, the prepared paper is removed from the negative, a picture the reverse of the negative will have been formed, in which the pigmented gelatine remains and performs the part of the reduced silver in the ordinary photograph. Photographic Varnish. See Varnishes.

The reader desirous of further information on the subject of photography cannot do better than consult Mr. Ernest Spon's valuable manual, entitled ' Workshop Receipts and Mr. Hughes' 'Principles and Practice of Photography,' to both of which works we are largely indebted. Captain Abney's work on ' Photography' cannot be too highly commended. Photography. - Miscellaneous Recipes.