Dimensional Changes in the Manufacture of Electrotypes
Electrotyping is a process by which printing plates are produced by the electrodeposition of metals. In this process the details of the original, whether type or halftone, are faithfully reproduced. However, it has long been known that, unless special precautions are observed, the resultant electrotypes are not exactly the same size as the originals. This difference, which in curved plates maybe greater than one per cent, is usually not significant if the printing is done only in one color, as then only one plate is involved. Even in one-color printing accurate reproduction may sometimes be required in such cases as in the printing of charts, scale diagrams, or cross-section paper. In multi-color printing, however, two or more plates are employed, one for each color used. For high-grade printing, these plates must have the same corresponding dimensions in order to register properly. Even in this case it is not essential that the various plates should be exactly the same size as the originals, but they must be the same size with reference to each other. As an example, an 8 x 10 inch four-color picture in a magazine may vary 0.1 inch or so in size in either or both directions and still give a perfect picture if all four plates are alike in size. On the other 2 hand, if any one or more of the color plates do not match the others in size by even 0.01 inch, the picture will be noticeably out of register.The object of this research was to study quantitatively the changes in dimensions of the electrotypes occurring in each of the steps of their manufacture, and to point out methods of control by which electrotypes of uniform size can be made.