VAN DYKES In printing from paper negatives and for making paper negatives from tracings, Van Dyke paper is used. This is known under several other names, such as black line process, brown print, and Maduro paper. While this process is somewhat similar to blue print, it differs in that it must be fixed in a weak solution of hypo, or some fixing agent of a like nature.
Commercial photographers also use this paper for making prints- from line negatives, copies of letters, etc., as it has no emulsion on it and it can be folded up and creased without injury, and as this paper is also very thin in certain grades, it is not so bulky as regular photographic paper.
This paper can be bought ready coated or you can coat your own, in which case, the following is a very good formula : No. 1.
Water 24 oz.
Ferric oxalate 6 oz.
Citrate of iron and ammonia (green) 3 oz.
Tartaric acid 3 oz.
Lactic acid 2 oz.
No. 2. Water 24 oz.
Nitrate of silver 3 oz.
Mix separately until dissolved, then mix to gether.
In large manufacturing plants, there is another machine that is found in nearly all the photographic departments and that is the photostat—see illus tration No. 80.
This machine is used to copy drawings, blue prints, letters, checks, pages from books, designs—in fact, there is scarcely any limit to its scope. The photographs are made directly onto a special bromide paper through the lens, a prism, thereby making them read right, and without the necessity of going through the usual negative and print process. The colors in a Photostat print are reversed, the black coming white, and white, black. Illustration No. 81 is of a Photostat copy of a tracing. If the original colors are desired, a second copy is made from the first Photostat print.
This machine is made in various sizes to fit almost all kinds of work and requires very little skill to operate.
The lighting equipment for a machine of this kind is generally of the Cooper Hewitt type, one type on each side of a horizontal copy board.
The copyboard is marked off with rectangles, which are given numbers to correspond with the length in inches, and there are corresponding numbers on the leg of the machine and on the Camera Bed to which the machine is set, so as to mechanically give the correct focus. The machine is also equipped with apparatus for developing and fixing the photographs, so that all of the work is done right in the machine itself, except for the washing and drying of the photographs.
In some places the Photostats are equipped with a light, tight conveyor, which shoots the photographs from the machine through a specially, arranged opening into a dark room, where the developing and fixing can be handled with somewhat greater rapidity.
When maps or drawings are larger than the regular copyboards, they can be copied just the same. Under these circumstances, the subject is hung on a wall or a screen at the side of the machine, and the prism turned at right angles to its regular position, so as to cover the subject which is to be photographed.
Occasionally, blue prints are made directly from the Photostat prints. When blue prints or Van Dykes are to be made in this way, better definition is obtained if the prism is removed, and the subjects to be copied hung on the wall and regular negative print made directly on the bromide paper. This negative print is then re-developed, the same as the sepia process in printing— that is, bleached out with ferricyanide and bromide and blackened with sulphide.