To develop by floating the print, place the print, exposed side down, in the developer by letting it slip evenly and quickly into the solution. Lift and see if any air-bubbles have formed on the surface of the print. If there are any, touch them with the tip of the finger or the corner of a card, and return the picture at once to the developer. The picture will develop quite fast, but it can be stopped at once by transferring the print to the acid bath.
The developer must be used in a porcelain or agate tray, and another tray—a glass tray such as is used for hypo will do—must be filled with the acid clearing bath so that the print may at once be placed in it as soon as it has been developed enough.
As soon as the print has developed enough remove at once, before washing, to the acid clearing bath. The prints must have three changes of the acid bath, leaving them in ten minutes each, and afterward wash them in three or four changes of water, lasting about half an hour altogether. Pin up to dry, blotting off the superfluous moisture with clean blotting-paper.
Developing with a brush is sometimes to be preferred to floating. Take a wide flat camel's-hair brush, turn some of the developer in a shallow dish, lay the print on a sheet of glass, face up, dip the brush in the developer, and beginning at the top of the print, brush it across from one side to the other, and then lengthwise of the print, using light even strokes. The picture will not be so evenly developed as by floating, but this unevenness may be remedied by floating the print for half a minute in the developer and then transferring quickly to the acid bath.
Stop the development as soon as the right depth has been brought out, and while the detail is perfect. If a print is developed too long the print will appear flat, as in the case of a negative when overdeveloped.
As platinum prints are more quickly made than aristo or albumen, this paper is very desirable for winter photographic printing.
The mounts for platinum prints have a plate sunk centre covered with India paper, and are usually of a soft gray color for the margin. The prints may be mounted on plain cards, but are much more effective if mounted on the cards prepared expressly for platinotypes.
The paper costs 50 cents per dozen for 4x5, 80 cents for 5x7. The paper can be bought in any size desired. The developing solution or salts cost 35 cents for a package containing enough to make 50 oz. of developer.