Here are some platinum toning baths well recommended:—

20.Lactic acid2drams.
Water12ounces.
Pot. chloroplatinite2grains.
21.Citric acid20grains.
Water10ounces.
Table salt20grains.
Pot. chloroplatinite 2grains.
22.Phosphoric acid3drams.
Water10ounces.
Pot. chloroplatinite 2grains.

The chief points to bear in mind in platinum toning are: (1) that the print must have practically all the free silver washed away before toning. To this end it is a very good plan to dip each print for a couple of minutes or so in a bath of table salt one ounce, water ten ounces, and again rinse under the tap for a minute or two.

(2) That the toning bath is acid, therefore one must either neutralize this acidity by passing through an alkaline bath, such as No. 19, or what perhaps is rather more convenient, though not quite so desirable—i.e., using a fixing bath made distinctly alkaline. The following proportions are recommended:—

23.Hypo1ounce.
Water10ounces.
Soda sulphite½ounce.
Washing soda½"

Toning with Gold and Platinum.—A large number of experimenters have tried to find out how to produce platinotype-like effects with P.O.P. papers. Perhaps none of them have been completely successful. The following procedure, however, seems to give the nearest approach to that ideal.

The best results are obtained with a slightly matt-surfaced paper. This should be printed a shade or two deeper than the print is intended to appear finally. The print is well washed and then partly toned in a gold bath:—

24.Soda acetate30grains.
Borax25"
Water10ounces.
Gold chloride1grain.

It is then washed for a minute or so, and the toning continued in the following bath.

25.Phosphoric acid1dram.
Water5ounces.
Pot. chloroplatinite2grains.