This is somewhat similar to Bromide Paper, but yields prints more resembling albumenized prints by a little manipulation in exposing and developing. The paper may be exposed in the ordinary printing frame to diffused daylight from one to twenty seconds, according to the actinic power of the light and density of the negative. It may also be exposed to gas or lamp light, and the printing frame should be placed at about six inches from the flame, and an exposure varying from thirty seconds to five minutes, will be found necessary. The process of development employed is usually the ferrous oxalate, recommended on pp. 28 and 83. The prints may be either soaked in water first, or placed in the dry state in the developer; if the latter plan is adopted it will be found that they will have a tendency to curl, but this may be avoided by laying the print face downwards for a second or two on the developer, and then turning them over, and immersing bodily in the developer. After development, the prints must be plunged at once into the following clearing solution, for one or two minutes: -
Alum ... ... ... ... ... 1 ounce.
Citric Acid ... ... ... ... ¼ ounce.
Water... ... ... ... ... 20 ounces.
After five minutes washing in several changes of water they may be placed in the following toning bath : -
Hypo... ... ... ... ... 2½ ounces.
Sodium Acetate ......... ½ounce.
Sulphocyanide Ammonium ... 4 ounces.
Chloride of Gold ... ... ... 4 grains.
Distilled water ......... 10 ounces.
Dissolve the ingredients in the order given.
The prints should be left in this bath till on looking through them the desired tone is obtained, then wash in running water for at least an hour, and hang up to dry; if an enamelled surface is desired they may be treated in the same way as recommended for gelatino-chloride prints (page 89).
The following general hints to ensure success and regularity of tone, will be found useful:-
Always use a good yellow light for the dark room illuminant when working this paper. Always use artificial light to expose by. Always place the printing-frame in exactly the same position; and give absolutely the same exposure to prints from the same negative. Clean hands are a sine qua non. Hypo should never be touched till all the prints are developed. Do not over-develope, as the prints lose nothing in toning and fixing. If the prints are too dense, a longer soaking in the alum bath will reduce them. Always keep prints on the move in all solutions. In hot weather immerse the prints in an alum bath (1 ounce of alum to 10 ounces of water) after they have been well washed on leaving the fixing and toning bath. Over-exposure is known by a poor, flat print full of half tone, but wanting in contrast and vigour in the shadows. Under-exposure, known by want of half tone and greenish tints in the shadows.
Alpha Paper like Bromide may be developed with Hydrokinone (for formulae see page 94), and gives very fine black tones by this method of development. It must, however, be well washed before being put into the clearing solution after development.
If the tone of the finished print, by either method of development, be unsatisfactory, it may be easily remedied by immersing the print, which if dry should be previously soaked in water until wet, in the Mercuric Chloride solution, page 29, till bleached, more or less, then washing thoroughly and redeveloping with Hydrokinone or Ferrous Oxalate; it must be remembered, however, that this is a process of intensification, and, therefore care must be exercised not to carry the bleaching and redevelopment too far, so as to block up the details. The print should then be placed in the ordinary fixing bath for five minutes, and thoroughly well washed.
By this, prints are obtained of a fine black colour by development, the image being formed by metallic Platinum, one of the most permanent metals known; the results are extremely pleasing and very permanent. The paper is sent out by the Platinotype Company in tin tubes, so as to preserve it from damp which is a sure destroyer of it. It is printed in the printing frame in the ordinary way, but the image is only partially visible, but it prints in about one-third the time of ordinary albume-nized paper. When printed deep enough it is developed upon a solution of neutral Oxalate of Potash, 130 grains to the ounce heated to a temperature of 150° to 170° Fahr. The print is placed face downward on the solution for 5 or 6 seconds, and is then placed immediately in a bath of hydrochloric acid (1 to 60), and after being moved about in this for ten minutes it is treated in the same way in two successive similar baths for like periods. The print is then thoroughly washed and pinned or hung up to dry and mounted in the ordinary way. For further directions the copious and complete directions issued with the paper must be referred to.