PLATINUM TONING The theory of platinum toning is the same as that of gold toning, explained under that heading, except, of course, that platinum is substituted for gold. The earliest form of bath consisted of 1 gr. of platinic chloride in 15 oz. of water, and it was not until the introduction of the platinotype printing process, when potassium chloroplatinite was made available, that platinum toning became almost if not quite as popular as gold for silver prints, particularly those upon matt papers. As with gold, almost any tone may be obtained.
Print-out Silver Papers.—Two stock solutions are necessary : A. Common salt . -I,- oz. 55 g.
Alum . . . 55 ,, Water . . . 10 „ 1,000 ccs.
This may be made up with hot water, and is ready for use when cold.
B. Potassium chloro platinite . . 4o grs. 9 g.
Water . . ro oz. 1,00o ccs.
The chloroplatinite is sold in sealed glass tubes containing 15 grs. Soak off the label, place the unbroken tube in the bottle or measure with the water, and break the tube while in the water. Each quarter ounce (120 drops) of the solution will contain r gr. of the chloro platinite ; the mixture should be kept in the dark. Tones may be varied from red-brown to warm black by using a mixture of from io to rho drops of B, 1 oz. of A, and io oz. of water, this quantity being sufficient for ten half-plate prints or their equivalent. The prints dry of a darker tone than they appear when wet ; and therefore toning should be stopped just before the desired tone is reached, judging the tone by looking through the prints. Toning invariably continues in a slight degree during the washing previous to fixing, unless a " stop bath " be used, such a bath consisting of Too grs. of sodium carbonate crystals in to oz. of water.
After toning, prints are washed and fixed as usual.
Alternative Baths for Silver Prints.—Some alternative baths will now be given.
Cowan's Bath Common salt . . to grs. 2.3 g.
Potass. chloroplatinite I „ •23 „ Chrome alum ( % sol.) 10 oz. I,000 ccs.
Phosphoric Bath Potass. chloroplatinite 4 grs. 2 g.
Phosphoric acid (sp. gr., 1•120) . . . r drm. 28 ccs.
Distilled water . 41 oz. 1,000 „ The phosphoric acid is the " acidum phosphor icum dilutum " of the British Pharmacopoeia.
Wash and fix as usual. (Many other acids can be used in this way.) Prof. gamias states that the phosphoric acid may be advantageously replaced by oxalic acid.
Platinum may be used in the combined: toning and fixing form. A good formula is : Sodium hyposulphite r oz. 1 ro g.
Lead nitrate . . 6o grs. 14 9, Alum . . . 6o „ )9 Sodium formate . 20 „ Formic acid . . drm. 6 ccs.
Platinum bichloride . 2 grs. •5 g.
Hot water . . io oz. 1,00o ccs.
Dissolve the lead and sodium formate in a small quantity of the water, then the " hypo " and the other ingredients (except platinum) in the remainder. Mix together, allow to stand in an uncorked bottle for 24 hours, and then add the platinum bichloride. The prints (P.O.P.) should_ be passed through a weak salt and water bath before toning.
A formula for the " Haddon " platinum toning bath is given in an article under that name. For platinum and gold baths (combined) see under " Gold and Platinum Bath." Bromide Papers.—Most of the above baths may be used for bromide papers, and the follow ing is recommended : Hydrochloric acid . 5o mins. r ccs.
Potass. chloroplatinite 5 grs. r g.
Distilled water . 10 oz. 1,00o ccs.
Toning for about twenty minutes should give a good black image. Wash, fix in " and wash again thoroughly.
C. W. Somerville's toner (1902) is as follows :— Potass. chloroplatinite 20 grs. g.
Mercuric chloride . ro „ 2.3 „ Citric acid . . 90 „ 200 Distilled water . ro oz. 1,000 cos.
I oz. of this will tone three or four half-plate prints in about twenty minutes ; the print is previously fixed and washed, and after toning, again fixed and washed. If the sepia toned print is immediately subjected to an ordinary developer as used for bromide paper, the black colour will return with great intensification, but washing will prevent this.
Lantern Slides.—Lantern slides of the gelatine variety may be toned by any of the above pro cesses, but the most widely used bath is Hydrochloric acid . i min. •2 cc.
Platinum chloride . I gr. •2 g.
Water . . . 10 oz. ',coo ccs.
This tones rapidly, but reduces slightly.