The print needs to be vigorous ; from the printing frame it passes into plain water for about two minutes, and in this the image develops up to a greater strength and of a reddish brown colour. It is then transferred to a weak " hypo " fixing bath (" hypo " 5o grs., water 5 oz.,) or to a io per cent. sodium sulphite solution, in which the print becomes a richer brown in colour. Finally, the print is washed for about half an hour, and dried.
American Kallitype.—In America much atten tion has been paid to kallitype, and many formulae and improvements have been intro duced. The Jas. Thomson process needs a " salting " and a " sensitising " solution : Salting Solution Ferric-ammonio citrate . . . zoo grs. 45 g.
Ferric oxalate . 120 „ 27 „ Potassium oxalate . 120 „ 27 „ Copper chloride . 6o „ ,, Oxalic acid . . 40 „ 9 ,, Gum arabic . . roo„ 22.5 „ Distilled water . . Jo oz. 1,000 ccs.
The paper (sized if velvety tones are desired) is coated with the above, dried, and treated with the sensitiser : Oxalic acid . . 20 grs. 4'5 g.
Citric acid . . zoo „ 45 ,, Silver nitrate . . 500 „ 112.5 „ Water . . io oz. 1,000 ccs.
When surface dry, complete the drying by gentle heat, but excess of heat will convert the ferric salt to ferrous. For printing, three or four minutes in sunlight is generally sufficient. The image appearing is chestnut brown upon a yellow ground, and printing should be stopped before the half-tones appear. The print is placed direct into clear cold water, where it will develop fully ; four changes of water, or about three minutes in running water, will be sufficient. After washing, fix in a weak ” hypo " bath (5o grs. to 32 oz.) ; a ten-minute immersion is generally sufficient. Wash in plain water for about half an hour and dry ; the resultant colour should be a good brown.
Single-solution Kallitype Sensitiser.—The fol lowing sensitiser is one of the simplest and most widely used for menu, note paper and post card work. Geo. E. Brown, who has advocated it, gives the following directions : 55 grs. of silver nitrate is dissolved in 4 or 5 dims. of distilled water ; and liquor ammonim (.88o), diluted with an equal quantity of water, is very carefully added. As the first drop or two is added, a copious precipitate of silver oxide is thrown down in the solution. Addition of more
ammonia solution will re-dissolve this precipi tate ; cease to add ammonia on the disappear ance of the last traces of the precipitate. Weak sulphuric acid is next added drop by drop until the faint odour of ammonia disappears. 40 grs. of green ferric ammonium citrate dissolved in 6 drms, of water is then added, and the liquid is complete. Stored in the dark or in a stone bottle, it will keep good for several months. It is applied to paper in the same way as other kallitype sensitisers, dried, and the paper treated as before described, namely, with water and " hypo." After-treatment.—Kallitype prints may be toned, reduced, re-developed, and intensified. For toning, a simple combined bath which works well is : Water, 8 oz. ; sodium hyposulphite, oz. ; gold chloride, 1 gr. Over-exposed prints may be reduced by immersing in a weak solution of hydrobromic acid, a suitable strength being 3o drops of the strong commercial acid to 1 oz. of water. One immersion for a minute or two will usually suffice ; the print is then washed well. Another method is to immerse the print in the weak acid for a few seconds only, and then transfer to a weak fixing bath of " hypo " and water for a few minutes ; this increases contrasts considerably, and much can be done in the way of getting good prints from weak negatives. As regards intensification, the image consisting practically of metallic silver, it can be subjected to the processes advocated for intensifying negatives and bromide prints, and even the uranium and sulphide processes of toning and intensification may be used. The kallitype print, unlike a bromide print or a negative, can be easily bleached in a solution of hydrochloric acid, and io drops of the acid added to i oz. of water rapidly removes the image and converts the silver into silver chloride. If the bleached picture is then well washed and exposed to a strong light, it may be developed with any clean working developer, as hydroquinone metol, etc. In this way a strong developer may be employed to produce a cold tone, or a weaker developer one of a warmer tone, and the tones can further be modified in a gold or platinum toning bath.