The preparation of the paper by this process is very simple, and requires very few manipulations, while the results, when prints are made, are pleasing and lasting. Prints in blue are so easily made as to be extremely convenient for making proofs from negatives, and they are well adapted for mottoes, plans, drawings, manuscript, circulars, and for representations of scenery, boats, machinery, etc., etc., and for engravers' use.
Ferro-prussiate paper can be procured from E. & H. T. Anthony & Co., or can be easily made by the following formula:
Float the paper until it lies quite flat upon a solution prepared as follows:
1. Water................ 2 ounces fluid.
Red prussiate of potash.. 120 grains.
2. Water................. 2 ounces.
Ammonia citrate of iron. 140 grains.
When these two are dissolved, mix them together and filter into a clean bottle.
The solution should not be exposed to a strong light, and the paper must be floated on it in a very subdued light, and in the same manner as paper is floated on a silver solution. When it no longer curls, but lies flat on the solution, take it by the corners and raise it slowly from contact, and hang it up to dry in a dark place. When dry, it can be used at once, or may be kept for future use by rolling it, prepared surface in, and placing it in a tin box or or other receptacle, free from light and dampness.
To make a print on this paper, place the prepared surface in contact with the negative in a printing frame and expose to sunlight.
The time of exposure will vary according to the density of the negative and the intensity of the light. The rule is to allow the light to act long enough for the portions which first turn blue to become gray, with a slight metallic luster. At this point remove the paper from the frame and place it in a dish of clean water.
It now gradually becomes a rich blue throughout, except the parts which should remain white. Change the water from time to time, until there remains no discoloration in the whites; dry, and the picture requires no further treatment.
The blue color may be totally removed at any time by placing the print in ammonia water.
This is the standard formula.
Float the paper for a minute in a solution of
Ferridcyanide of potash...........1 ounce.
Dry in a dark room, and then expose beneath a negative until the dark shades have assumed a deep blue color, then immerse the print in a solution of
Bichloride mercury..............1 grain.
Wash the print, and then immerse it in a hot solution of
Oxalic acid....................4 drachms.
Water.................. ... 4 ounces.
Wash again, and dry.
Float the paper on a solution of the sesqui-chloride of iron. Dry and expose, afterwards wash the prints, and then immerse them in a bath of ferrid cyanide of potash. The picture will appear of a blue color in all those places where the sun has acted.
The paper, without having undergone any preceding preparation, except that of having been excluded from the light for several days, is floated on a bath of the nitrate of uranium as follows:
Nitrate of uranium............. 2 drachms.
Distilled water...............10 drachms.
The paper is left on the bath for four or five minutes, it is then removed, hung up and dried in the dark room. So prepared, it can be kept for a considerable time.
The exposure beneath a negative varies from one minute to several minutes in the rays of the sun, and from a quarter of an hour to an hour in diffused light. The image which is thus produced is not very distinct, but comes out in strong contrast when developed as follows:
Distilled or rain water..........2 drachms.
Nitrate of silver................7 grains.
Acetic acid...................a mere trace.
The development is very rapid in this solution. In about half a minute it is complete. As soon as the picture appears in perfect contrast, the print is taken out and fixed by immersion in water, in which it is thoroughly washed.