VII. PHOTOGRAPHY. 211 



962b. Actinometers, or instruments for ascertaining the 

 intensity of the action of the light, and by which the exposure of 

 the sensitive pigment paper under the negative is regulated. 



Johnson's, Vogel's, Spencer's, Lambert's, Sawyer's, Burton's, 

 Vidal's. The Autotype Company. 



Chemicals Employed. 

 Granulated bichromate of potash. Chrome alum. 



Colours. 



Indian ink, vegetable black, Paris black, plumbago, Indian red, Venetian 

 red, vermillion, purple madder, brown madder, vandyke brown, indigo, lac de 

 vin, various kinds of gelatines. 



962c. Pigmented Papers, in various colours, with subjects 

 printed to show the various shades. 



962d. Transfer Papers (i.e., papers prepared with insoluble 

 gelatine, and upon which the pictures finally rest). 



962e. Sawyer's Patent Flexible Support (being paper 

 prepared with insoluble gelatine and an aqueous solution of lac, 

 upon which the picture is first developed previously to its transfer 

 to the final support. The Autotype Company. 



962f. Reversing Mirror, being a piece of plate glass 

 polished to a perfectly true plane, and silvered by a chemical 

 process used to produce reversed negatives, enabling them to be 

 printed by the single transfer process of permanent pigment 

 printing. The Autotype Company. 



962g. Wave Bath, for nitrate of silver solution (being a new 

 and convenient form for sensitizing large plates with a compara- 

 tively small quantity of solution. The Autotype Company. 



962h. Sawyer's Callotype Process. 



The Autotype Company. 



Glass plates prepared with gelatine and isinglass, potassium dichromate, 

 &c., hardened by a spirituous extract of gum resins, upon which the photo- 

 graph is impressed by the action of light ; after which they are placed in a 

 type printing press, damped, and inked by lithographic rollers. 



(a.) Plate in first stage of preparation. 



(6.) Plate ready for exposure under negative. 



(c.) Plate after exposure under negative. 



(rf.) Plate after being inked up in the press. 



(<?.) Plate with the same picture partly showing on the paper and partly 

 on the plate. 



988i. Four Prints from Photographs, by Paul Pretsch's 

 mechanical process. Robert Saline, Regent's ]*<ii'k. 



O 2 



