THE URANIUM PROCESS.
As this is not really a toning process, but a modified form of intensification, it is essential that a proper print should be made. It must be somewhat lighter and weaker than would be required in the ordinary way, but how much lighter will depend upon the colour that is to be pro duced. The longer the " toning " the redder the colour, and as the longer the toning the greater the increase of intensity, it follows that the redder the tone desired the weaker and lighter should be the print, otherwise it will appear too hard and dark. It is also essential that the print should be produced by one of the non staining developers, not by the ferrous oxalate. The presence of iron in the print will cause blue green spots. The print must be thoroughly fixed and washed be fore treatment. The following bath is recommended : Uranium nitrate, 20 grs. ; potassium fcrricyanide, 18 grs. ; acetic
acid, oz. ; water, 10 oz. In making up this bath, it is essential that the ferri cyanide (or red prussiate of potash) should be in good condition. If it has been much exposed to the air it will be covered with a yellow powder, which leads to bad results. When in this condition it should he washed free from this yellow prussiate. Cover a few of the crystals with water, swill round for a moment, and decant off. Then scrape them out on to a clean filter paper or blotting-paper, and dry thor oughly. They may be placed in the oven to dry. The crystals should now be quite clear and of a bright ruby colour. Dis solve them in half the water, and the uranium salt in the other half, and pour the former into the latter, and when the acetic acid is added a clean red solution should result.