The term is applied to processes of making metal relief blocks. The manipulation is somewhat similar to that just described. A full description will be found under Photo-engraving.
The Mosstype process is a photo-engraving process, differing slightly in detail from that described. This is first made in a composition of asphaltum, sulphuretted resin, and caoutchouc, and from these a second mould of plaster is made, from which a casting is made in type metal to form the printing block.
Among the photo-etching processes are photo-zincography, zincotype, typogravure, and chromo-typogravure.
The term is one that is applied to many differently detailed processes in which designs in adhesive transfer ink are transferred to zinc plates in the same manner as transferred to stone in photo-lithography. An etching agent is then applied which eats into the zinc at the unprotected parts, producing the design on the zinc in low relief. See Photo-zincog raphy.
In Zincotypes the zinc is first coated with bitumen or bichromated gelatine or albumen, and exposed under the negative. The image is then developed. If the bitumen is employed, oil of turpentine is used as the solvent, but in the other method the albumen is first coated with printers' ink, and then developed by gently rubbing in cold water with a tuft of cotton wool. The unprotected parts of the zinc are then washed away.
For producing these blocks in half-tones a variety of methods are employed of breaking up the negative image.
The Typogravure process is a method of obtaining half-tone pictures from copper relief plates, worked by Messrs. Boussod, Valadon & Co., at Asnieres, near Paris. The details of the process have never been published. Chromo-typogravures are produced by the same means, a number of different plates being used with different colored inks to form the many-colored image.
In the last class, i.e., those processes in which the picture is printed from an intaglio copper plate, we have photogravure, Goupil-gravure, and photo-aquatint. The idea of producing copper intaglio plates by means of photography was first worked out by Niepce ; many others followed.
About 187o or '71 Woodbury suggested to Goupil & Co. a method of photogravure which was taken up and worked by that firm with great success. A gelatine relief was made in the same manner as for the Woodbury-type process, except that a fine gritty powder was added to the gela tine to give the necessary grain. From this relief a mould and an electrotype are made. Other processes are described under Photogravure.
The process is a method of making facsimiles of water-color drawings. The plate is carefully inked in by hand with the different colored printing inks, and the picture printed by one impression. The plate is cleaned and again inked for the next picture. The method of printing is, of course, very costly, as skilled artists have to be employed for coloring the plates. The results, however, are truly fine, and in some cases hardly distinguishable from the original water-color drawing.
By the process images are made from intaglio copperplates in a similar manner to photogravure. It is chiefly used for the reproduction of portraits taken direct from life.
This sketch of the different photo-mechanical printing processes is necessarily very in complete. Correct information regarding these is very difficult to obtain •, all firms working the processes naturally keep the details as close a secret as possible. More detailed descriptions of the most important are given in their respective places.
contrivance for calculating the intensity of light. See Actino meter.
process of measuring the relative amount or intensity of light emitted by different sources.
photo-mechanical printing process similar to Collotype.
science of photographing microscopic objects. Consider able strides have been made in this within the last few years, and the aid given to the micro scopists is incalculable. Hitherto skilled artists were required to draw what was visible to the eye. This was in most cases a difficult matter, as the structure of nature's works is so intricate and delicate that magnified objects could rarely be reproduced by hand with fidelity.