The above bath is calculated for the use of amateurs, who will only have a few sheets to sensitise. For larger quantities, the bath recommended by Mr. H. N. King is one of the best. Prepare two separate solutions.
A. Nitrate of Silver . . . . . . . 2 oz.
Sodium Nitrate (pure) . . . . • . 1 „Loaf Sugar . . . . . . . . so grs.
. . . . . . . . . 25 oz.
B. Nitrate of Silver . . . . . . . 2 oz.
Sodium Nitrate . . . . . . 1 „ Loaf Sugar . . . . . . . . 6o gr.
. . . . . . . . . to oz.
Use Solution A with about 1 oz. Solution B, for sensi tising the first four sheets of paper. After every four sheets add about 1 oz. of Solution B, rock the whole well, and proceed to sensitise the next 5 sheets, and so on. By this means the bath will be always kept at about the same strength. Dust and scum on the surface of the bath may be removed by drawing a piece of pure chemical blotting paper or filter paper across the surface. A little kaolin kept in the bottle will always keep it clear. If the paper is required to be kept for some time it is usual to draw it slowly through distilled water to which a little citric acid has been added.
Measles.—A disagreeable outbreak after printing of red spots, which do not tone to the same colour as the rest of the print, is known as " measles." It is generally attributed to the lack of any substance with which the chlorine can combine when liberated from silver chloride during printing. Hence it attacks the albuminate. There should be a little free nitrate of silver left in the paper by the sensitising process. Paper that has been acidified for keeping purposes should be exposed to the fumes of •88o ammonia before printing. Or such paper may be kept between sheets of blotting-paper, which have been dipped in a 5 per cent. solution of potassium nitrite and then dried. Albumen paper should always be kept under pressure until time of using, and in hot climates must not be allowed to get too dry.
Toning.—Albumen papers need not be printed quite so deeply as gelatine papers ; the loss in the toning bath is not so great. The paper for prints from a given negative should always be cut the same way out of the sheet, because paper shrinks during the long immersion in water, and the shrinkage is always greatest in the direction of the fibre.
When the high lights take on a pink tinge, and the shadows show signs of bronzing, remove from the printing-frame, wash until the milky deposit ceases to come away, and immerse in the toning bath.
Acetate Toning Bath.— Gold Chloride . . . . . . . . 15 gr.
Sodium Acetate . . . . . . . i oz.
Water . . . _ . . 20 „ For use take i oz. of this stock solution and make up with water to 8 oz. to tone one sheet of prints. Our own way of mixing the stock solution is to first dissolve the acetate in to oz. of water in a pint bottle, and drop the 15 gr. tube of gold into the bottle. A brisk shake will break the tube against the side of the bottle, and the remainder of the water may then be added. This toning bath will keep for months if protected from strong light, but must not be used within twenty-four hours of mixing. It will give rich, warm tones.
Phosphate Toning Bath.— Chloride of Gold Phosphate of Soda . . . . . . . 20 „ Water 8 oz.
The phosphate bath gives deep purple tones, but must be used very shortly after it has been prepared.
Fixing Batk.—Wash the prints after toning in two changes of water, and then fix for ten minutes in Hypo . . . . . . . . 4 oz.
Water . . . . . . • . . zo „ Ammonia . 20 min.
If blisters appear at any stage introduce a little chloride of sodium (common salt) into the next washing water. The subsequent washing and drying are the same as for gelatino chloride papers.
Plain Salted Papers.—There are several receipts in common use for sizing and sensitising these home-made papers. A good pure unsized paper, free from all traces of iron, must be taken for the foundation, either Whatman's, Saxe's, Rive's, or Joynson's. Float on one or other of the following sizing baths : (1) Gelatine . . . , . 120 gr.
Ammonium Chloride . . . . . . zoo „ Water . . . . . . . zo oz.
The gelatine is first swelled in cold water ; then the remainder of the •water is added warm with the chloride, and heat applied until the gelatine is dissolved.