A number of the formulas given in various parts of this work may be applied to the home preparation of picture postcards. Under this heading we supply one or two methods for utilising in photography the ordinary postcards sold by stationers in penny packets.
Soak the cards for about a minute in:
Sodium Chloride.......50 gr.
And dry on a newspaper before the fire; then sensitise the portion that is to receive the print by spreading on with a brush or pledget of cotton-wool a solution of:
Nitrate of Silver.......90 gr.
Citric Acid........ 2 „
Water......... 2 oz.
Dry rapidly in subdued light, and print under a masked negative. Print deeply, tone in the acetate gold bath, and fix in the usual hypo bath.
The following is recommended by Mr. C. A. L. Pearson in the Camera:
Silver Nitrate........80 gr.
Tartaric Acid........40 „
Citric Acid........15 ,,
Potassium Bichromate (solution 10 gr. per oz.) . 4 drops Water......... 1 oz.
Dissolve the silver in a portion of the water, add tartaric acid, and stir with glass rod. Then add the ammonia until the precipitate at first formed is redissolved, then bichromate solution with more ammonia, if the red precipitate does not redissolve on stirring, and lastly the remainder of the water. Keep in a stoppered bottle away from light. Paper sensitised with this solution should be printed rather lighter than is required for the final effect, as the image afterwards darkens. Dip for a few seconds in a 2 per cent. solution of common salt without washing, and fix for ten to fifteen minutes in a strong hypo bath.
A yellow glass bottle is recommended for the preparation of the emulsion with which the cards are to be coated.
Gelatine (Coignet's No. 1)..... 40 gr.
Barium Chloride...... . 8 ,,
Nitrate of Silver . . . . . . . 20 ,,
Methyl Alcohol....... 1/2 dr.
Water......... 1 oz.
Pour in the distilled water, then add the chloride and the gelatine; let them soak for half an hour and warm to about 950 Fahr. When the gelatine is dissolved add the silver, shaking until dissolved, and then the alcohol. Keep for half an hour at 95°, and then coat paper. The salting may be altered to suit conditions, highly salted emulsions being naturally suitable for rich tones and dense negatives. Pour a small pool in the centre of the paper and spread quickly over the surface with a brush. This emulsion tones excellently in the sulphocyanide combined bath; and we have got good results with the acetate and other toning mixtures.