Part 351

A very satisfactory solution may be made as follows:

Sodium phosphate 20 grains Gold chloride 1 1⁠/⁠2 grains Distilled (or boiled) water 10 ounces

This tones very quickly and evenly, and the print will be, when fixed, exactly the color it is when removed from the bath. Good chocolate tints may be obtained, turning to purple gray on prolonged immersion.

Next to this, as regards ease of manipulation, the tungstate bath may be placed, the following being a good formula:

Sodium tungstate 40 grains Gold chloride 2 grains Water 12 ounces

The prints should be toned a little further than required, as they change color, though only slightly, in the hypo. {541}

Provided that ordinary care be exercised, the sulphocyanide bath cannot well be improved upon. The formulas given by the various makers for their respective papers are all satisfactory, and differ very little. One that always acts well is

Ammonium sulphocyanide 28 grains Distilled water 16 ounces Gold chloride 2 1⁠/⁠2 grains

For those who care to try the various baths, and to compare their results, here is a table showing the quantities of different agents that may be used with sufficient water to make up 10 ounces:

Gold chloride, 1 gr. to 1 oz. water 12 dr. 16 dr. 16 dr. 11 dr. 11 dr. 14 dr. Borax 60 gr. Sod. bicarbonate 10 gr. Sod. carbonate 20 gr. Sod. phosphate 20 gr. Sod. tungstate 40 gr. Amm. sulphocyanide 17.5 gr.

We may take it that any of these substances reduce gold trichloride, AuCl_〈3〉 to AuCl; this AuCl apparently acts as an electrolyte, from which gold is deposited on the silver of the image, and at the same time a small quantity of silver combines with the chlorine of the gold chloride thus:

AuCl + Ag = AgCl + Au

When toning has been completed, the prints are washed and placed in the fixing bath, when the sodium thiosulphate present dissolves any silver chloride that has not been affected by light.

Besides the well-known, every-day tones we see, which never outstep the narrow range between chocolate brown and purple, a practically infinite variety of color, from chalk red to black, may be obtained by a little careful study of toning baths instead of regarding them as mere unalterable machines. Most charming tints are produced with platinum baths, a good formula being

Strong nitric acid 5 drops Water 4 ounces Chloro-platinite of potassium 1 grain

The final tone of a print cannot be judged from its appearance in the bath, but some idea of it may be got by holding it up to the light and looking through it. A short immersion gives various reds, while prolonged toning gives soft grays.

Results very similar to platinotype may be obtained with the following combined gold and platinum bath:

A.—Sodium acetate 1 drachm Water 4 ounces Gold chloride 1 grain

B.—Chloro-platinite of potassium 1 grain Water 4 ounces

Mix A and B and neutralize with nitric acid. (The solution will be neutral when it just ceases to turn red litmus paper blue.)

Another toning agent is stannous chloride. Two or three grains of tin foil are dissolved in strong hydrochloric acid with the aid of heat. The whole is then made up to about 4 ounces with water.

«Toning Baths for Silver Bromide Paper.»—The picture, which has been exposed at a distance of 1 1⁠/⁠2 feet for about 8 to 10 seconds, is developed in the customary manner and fixed in an acid fixing bath composed of

Distilled water 1,000 cubic centimeters Hyposulphite of soda 100 grams Sodium sulphite 20 grams Sulphuric acid 4 to 5 grams

First dissolve the sodium sulphite, then add the sulphuric acid, and finally the hyposulphite, and dissolve.

Blue tints are obtained by laying the picture in a bath composed as follows:

A.—Uranium nitrate 2 grams Water 200 cubic centimeters

B.—Red prussiate of potash 2 grams Water 200 cubic centimeters

C.—Ammonia-iron-alum 10 grams Water 100 cubic centimeters Pure hydrochloric acid 15 cubic centimeters