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image, water and immersed

INK PROCESS.—A method of obtaining positive prints in ordinary writing ink. A good quality of paper is first immersed in a nearly saturated solution of potassium dichromate, and dried in the dark. When dry, the paper will have a bright yellow color. It is then placed under the negative in a printing-frame and printed until all the details appear. The picture will appear as a brownish image on a yellow ground. The time required in printing is somewhat less than tor albumenized paper.

The prints are first washed in water to eliminate the undecomposed chromium salts. The washing operation must take place in the dark, and requires about two or three hours with run ning water. The print is now fixed, and should appear as a brown image upon a white ground.

The next process is to color the image black or purple. This is accomplished by causing writing ink to adhere to the dark portions of the picture, acting as a mordant. To do this the

print is immersed in a weak aqueous solution of ferrous sulphate (five grains to the ounce of water), and allowed to remain therein for a few minutes, when it is removed, immersed in a weak solution of hypochloric acid for 15 minutes, and thoroughly washed in several changes of water. It is then immersed in a strong solution of tannin (20 grains to the ounce), when the image will instantly turn black, this change being due to the formation of tannate of iron or writing ink. The light should remain unchanged if the print has been properly exposed.

INSENSITIVENESS.—The insensitiveness of substances which should be sensitive is usually caused by careless manipulation or faulty chemicals, the action of light having little or no effect upon them. In many cases time will also render sensitive material insensitive.