1851 Great Exhibition: Official Catalogue: Class X.: Henneman and Malone
297. HENNEMAN and MALONE, 122 Regent St., Westminster — Designers.
1. Talbotype apparatus of improved design, made by J. Newman, of 122 Regent Street.
2. Talbotype pictures produced on paper, silk, and other fabrics; and on porcelain, coated glass, stone, steel, wood, and ivory.
3. Talbotypes treated with caustic potash and a lead salt, in order to produce an agreeable tint of colour, and to render more secure the fixation.
4. Specimens of Sir J. Herschel's cyanotype and chrysotype, and of Mr. Robert Hunt's chromatype pictures.
[Talbotype is the name applied, in the first instance, by Sir David Brewster, to the calotype pictures, his object being to distinguish by the name of the discoverer a photographic process which is little, if anything, inferior to the daguerreotype of the French. Paper being covered with a pure iodide of silver, is rendered sensitive to luminous radiations by being washed over with a mixture of gallic acid and nitrate of silver; and after the paper is taken from the camera, a dormant picture being produced upon it, it is developed by a second application of gallic acid.
Sir John Herschel's cyanotype and chrysotype processes admit of many modifications, the former consisting of the change of a persalt of iron into a protosalt by the solar rays; the paper being then washed with a compound of cyanogen (hence its name), the picture is represented in Prussian blue.
The latter is in most respects similar, only that a solution of gold is applied to the altered iron salt, and oxide of gold is formed in the place of Prussian blue.
The chromatype is formed by washing paper with a mixture of the bichromate of potash and sulphate of copper; and after the picture has been faintly developed by the chemical principle of the solar beam, it is washed with nitrate of silver, by which a positive picture, or one with correct lights and shadows, is produced by one operation.—R. H.]