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A NEW MEDIUM FOR THE PRODUCTION O£ VANDYKES1
L. S. TRIMBLE**
Summary. — As the result of Army complaints on the printing quality of Vandykes, or brown line print master negatives, aircraft companies have spent considerable time and effort in expensive tracing heavy-up work.
Lockheed has specified and had prepared a new and different type of Vandyke paper having sufficient latitude and contrast to produce acceptable prints from combination pencil and ink line tracings. The paper carries a slow photographic emulsion, is processed on the standard blueprint machines under normal operating conditions, and can be furnished at the approximate cost of the present Vandyke paper.
In order to speed production, it is customary for war plants to prepare direct pencil drawings of parts or structures on a thin tracing paper suitable for use in blueprint reproduction. With the extended distribution of war materials, it became necessary for the Armed Forces to prepare copies of certain of these prints. Specifications called for the preparation of a master negative as a Vandyke, suitable for use in the contact printing of blue line positives.
The method of preparing Vandykes, or master negatives of tracings for subsequent blue line reproduction, involves the following:
(1) The original drawing or tracing is prepared with pencil on tracing paper. If the lines are sufficiently heavy, a Vandyke can be made by direct contact printing, however, a copy cloth photographic-type positive is often made from this tracing to gain contrast, minimize spots and dirt, and provide a durable record for use in the Engineering Department. This print is often corrected with either ink or pencil lines and sometimes both.
(2) A Vandyke negative is made from the copy cloth positive. The Vandyke consists of a pretransparentized 100 per cent rag, 12-1 6-lb paper base coated with silver salts and suitable halide acceptors such that following exposure to light and treatment in a sodium thiosulfate solution, the exposed sections are converted to brown silver or silver sulfide.
A print made in the above manner from a copy cloth bearing ink and pencil corrections fails to reproduce all lines sufficiently different
* Presented Oct. 17, 1944, at the Technical Conference in New York. ** Lockheed Aircraft Corporation, Burbank, Calif. 54