I have used the following receipt for blueprints with much satisfaction. The same formula may be applied for postal cards on which it is desired to print landscapes or similar views. Make a solution as follows: Water, 3 ounces; ammonia citrate of iron, 300 grains; oxalate of potash, 75 grains. Dry in the dark, print and then develop in the following: Water, 3 ounces; nitrate of silver, 15 grains; citrate of soda, 150 grains. Add ammonia to dissolve the precipitate, and acetic acid until slightly acid. Wash slightly and dry. I have found this to make a better blue-print in every detail than any other of the various known receipts. Robert B. Otis.
To make blue-print paper use citrate of Iron and ammonia, 1% ounce dissolved in 8 ounces of water, and red prussiate of potash, 1 ¼ ounce, dissolved also In 8 ounces of water. Keep in separate bottles until wanted for use. When wanted for use, measure equal quantities from each of the above bottles. Shake so as to mix it well. It is then ready for putting on the paper. When the two are poured together, the mixture must be kept away from white light and should be applied in a room illuminated with a ruby light only. The paper must be dried in this room and kept in the dark until used. One ounce of mixed chemical will cover about 4 square feet of paper. David Melville.
To prepare the blue-print solutions, dissolve 3% 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 blue-prints 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 blue-prints 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. Julian Day Page.