This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
A vegetable coloring matter. Dark, copperish-red, semi-metallic mass. When powdered, is deep blue in color. Insoluble in water, cold alcohol or ether; slightly soluble in boiling water; very soluble in sulphuric acid. Used in preparing various solutions for chemical tests.
An optical term denoting the point at which a lens may be set when focusing on an object far enough removed from the camera so that the rays of light proceed towards the lens in practically a parallel manner. This distance must be over 100 feet. When the lens is at this point, all objects within certain definite limits will be perfectly sharp on the plate or ground-glass. The distance from the lens to the nearest object that will be sharp when the lens is set at the point of infinity, varies with the aperture and focus of the lens, but it may be assumed to be 50 times the focus of the lens with a stop at F. 8. All objects beyond this point will be in focus. The smaller the aperture, the nearer to the lens will objects be in focus.
Gum Arabic, 1/2 ounce; water, 2 ounces. Strain through muslin and then add a sufficient amount of zinc white to make the ink smooth. If too thick, dilute with water. Add a few drops of carbolic acid as a preservative.
Very speedily; done in an instant. The making of an exposure of rapidly moving objects. The camera may be held in the hand during the exposure and a perfectly sharp record obtained of the object in motion.
(See Shutter, Instantaneous.)
Prepare the following solution:
To this add two or three drops of a 20 grain solution of silver nitrate. The silver nitrate solution must not be added, however, until the time of using. With this solution any degree of density may be obtained, and care must be taken not to intensify too much, as the color of the film becomes very non-actinic. If the solution remains on the plate for any length of time it will cause stain; therefore, immediately after intensifying, the plate should be thoroughly washed and then dried slowly. Although the acid has a tendency to cause frilling of the film, there will be little danger from this source if the temperature of the solution is maintained at a moderately low degree - 50o to 65° Fahr.