KALLITYPE A printing process invented by Dr. W. J. Nichol in 1899. Paper, coated with a mixture of a ferric salt and silver nitrate, gives, on expo sure to light behind a negative, an image in ferrous oxalate and silver oxide which, on the application of a suitable developer, precipitates an image in metallic silver. The principle of the process is old, and was foreshadowed by Hers chel's obsolete " Chrysotype " process. The instructions immediately following are practically those originally published by Nichol, who at one time placed the paper ready for use on the market but withdrew it because he was not satisfied with the permanency of the results ; his fixer was a weak solution of ammonia, but later experiments proved that the use of " hypo " as a fixer gave more permanent prints.
The paper preferably after sizing, is sensi tised by coating with : Ferric oxalate . . 75o grs. 167.5 g.
Silver nitrate . . 300 „ 67 „ Oxalic acid . . q.s. q.s.
Distilled water . 10 oz. I,000 ccs.
Place the ferric oxalate in a bottle with the water, which stand in a saucepan of water, and gradually heat until the ferric oxalate dissolves. If there is need, add not more than from 5 to io grains of powdered oxalic acid to assist solu tion. Filter the hot solution, and add the silver nitrate to the clear filtrate ; this will keep good in the dark for several months. The paper is then coated (in a yellow light) after the manner described under the heading " Blue-print Pro cess," dried, and printed upon until of a bluish brown colour upon a yellow ground. At this stage the image consists of reduced iron (ferrous) salt which has the power of reducing the silver nitrate to a metallic state, which power, however, is latent until a developer (a solvent of the ferrous salt) is applied to the paper.
Of the many possible developers, the chief are sodium tungstate, Rochelle salt, sodium acetate, and borax.
(1) For Black Tones— Borax . . . I OZ. 110 g.
Rochelle salt . . „ ,, Potassium bichromate (I % solution) .7-9 drms. 87-112 ccs.
Water . . . Io oz. 1,000 „ (2) For Sepia Tones— Rochelle salt . . oz. 55 g.
Potassium bichromate (1 % solution) • drms. 50-62 ccs.
Water 10 oz. 1,000 „ (3) For Purple Tones— Borax . . . oz. 27.5 g.
Rochelle salt . .1 IIO „ Potassium bichromate (I % solution) .7-9 drms. 87-112 CCS.
Water . . . 10 oz. 1,000 „ (4) For Maroon Tones— Rochelle salt . . i oz. i io g.
Sodium tungstate . „ 55 Water . . . 10 „ 1,000 ccs.
The print is immersed in the developer and the dish is rocked for from fifteen to thirty minutes. Although the image may appear quickly, the print must remain in the bath some time in order to render the iron salts completely soluble. The print is then passed direct, without washing, into the fixing bath, consisting of— Sodium hyposulphite 1 oz. 55 g.
Liquor ammonia? (•880) 4.„ ccs.
Water . . 20 „ 1,000 „ The print is kept on the move in this bath for about ten minutes, then washed for about twenty minutes, and finally dried. Some advocate a second immersion in a fresh fixing bath (as above) in order to be sure of thorough fixing, which is absolutely necessary to secure permanent pictures.
A finished kallitype picture has an image consisting of metallic silver, and it may there fore be toned with gold, platinum, or by the sulphide process, if desired.
Modified Kallitype.—Another and more mod em paper is that known as " Water-developing kallitype," which is a good paper for home pro duction, but the warm brown results cannot, as a rule, be said to equal those given by the proper kallitype process described above. Four solutions are necessary for sensitising : A. Green ferric am monio-citrate . grs. 252 g.
Water .. . io oz. i,000 ccs.
B. Tartaric acid . 180 grs. 41 g.
Water . . . 10 oz. 1,000 ccs.
C. Silver nitrate . 46o grs. 106 g.
Water . . . 10 oz. 1,000 ccs.
D. Gelatine . . 3c0 grs. 69 g.
Water . . . 10 oz. 1,000 ccs.
The A and C solutions keep well in the dark ; the B solution keeps for a few days only, owing to the formation of mould ; while the D solution should be made just before use, the gelatine being soaked in the water and dissolved by heat. Equal parts of the four solutions added together form the sensitiser ; A and B solutions should be added to the warm gelatine D, the whole being kept warm by placing the measure, say a io oz. graduate, in hot water. The C solution is then added very slowly, stirring the combined mixture with a glass rod the while. The warm solution is then coated upon the plain paper, and as soon as the coating has lost its wet appearance and begins to look dull the paper is hung up in a warm room and out of the way of actinic light to dry ; when dry it is ready for printing.