This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
The ordinary blue photographic print in which white lines appear on a blue ground may be made on paper prepared as follows: A.—Potassium ferricya-
nide.............. 10 drachms
Distilled water....... 4 ounces
Iron ammonia citrate. 15 drachms
Distilled water....... 4 ounces
Mix when wanted for use, filter, and apply to the surface of the paper.
With this mixture no developer is required. The paper after exposure is simply washed in water to remove the unaltered iron salts. The print is improved by immersion in dilute hydrochloric acid, after which it must be again well washed in water.
The following process, credited to Captain Abney, yields a photographic paper giving blue lines on a white ground: '
Common salt....... 3 ounces
Ferric chloride...... 8 ounces
Tartaric acid....... 3.25 ounces
Acacia............ 25 ounces
Water............. 100 ounces
Dissolve the acacia in half the water and dissolve the other ingredients in the other half; then mix.
The liquid is applied with a brush to strongly sized and well rolled paper in a subdued light. The coating should be as even as possible. The paper should be dried rapidly to prevent, the solution sinking into its pores. When dry, the paper is ready for exposure.
In sunlight, 1 or 2 minutes is generally sufficient to give an image; while in a dull light as much as an hour is necessary.
To develop the print, it is floated immediately after leaving the printing frame upon a saturated solution of potassium ferrocyanide. None of the developing solution should be allowed to reach the back. The development is usually complete in less than a minute. The paper may be lifted off the solution when the face is wetted, the development proceeding with that which adheres to the print.
When the development is complete, the print is floated on clean water, and after 2 or 3 minutes is placed in a bath, made as follows:
Sulphuric acid...... 3 ounces
Hydrochloric acid.. . 8 ounces Water...........'. . 100 ounces
In about 10 minutes the acid will have removed all iron salts not turned into the blue compound. It is next thoroughly washed and dried. Blue spots may be removed by a 4 per cent solution of caustic potash.
The back of the tracing must be placed in contact with the sensitive surface.
Dissolve 3.75 ounces of ammonia citrate of iron in 18 ounces of water, and put in a bottle. Then dissolve 2| ounces of red prussiate of potash in 18 ounces of water, and put in another bottle. When ready to prepare the paper, have the sheets piled one on top of the other, coating but one at a time. Darken the room, and light a ruby lamp. Now, mix thoroughly equal parts of both solutions and apply the mixture with a sponge in long parallel sweeps, keeping the application as even as possible. Hang the paper in the dark room to dry and keep it dark until used. Any of the mixture left from sensitizing the paper should be thrown away, as it deteriorates rapidly.
Often, in making blueprints by sunlight, the exposure is too long, and when the frame is opened the white lines of the print are faint or obscure. Usually these prints are relegated to the waste basket; but if, after being washed as usual, they are sponged with a weak solution of chloride of iron, their reclamation is almost certain. When the lines reappear, the print should be thoroughly rinsed in clear water.
Often a drawing, from which prints have already been made, requires changing. The blueprints then on hand are worthless, requiring more time to correct than it would take to make a new print. An economical way of using the worthless prints is to cancel the drawing already thereon, sensitize the reverse side, and use the paper again.