Julius Schnauss

Collotype in Natural Colours.

A SHORT chapter may be devoted to the various suggested processes for producing Collotype in natural colours, with which are associated the names of Vidal, Albert, and Obernetter. To give a complete resume is altogether impossible, as up to the present time the inventors have only published their method of procedure with very considerable reservations, and notwithstanding the fact that a great deal has been written and published in current literature on the subject, little is actually known. The methods of Vidal and Albert are essentially alike, both being founded upon an opti-chemical basis. By careful registration and printing from three Collotype plates, representing fragments of the same subject upon one sheet of paper, and making use of inks corresponding with the three primary colours, a total effect should be produced which ought, theoretically, to resemble the coloured original. In preparing the three negatives for reproducing the three colour plates a special mode of procedure must be adopted. Each of the three negatives must give a resulting Collotype plate capable of retaining varying amounts of ink when rolled up, according to the predomination in the original of one or the other of the primary colours—red, blue, or yellow.[M] This is effected in the production of the negative for the red plate, by making the exposure through a green glass screen, while the negative intended to produce the plate from which the yellow is to be printed is exposed through a screen of violet.

The green screen allowing to pass so few chemically active rays the exposure has to be prolonged to such an extent that gelatine bromide dry plates stained with eosine must of necessity be used.

Obernetter’s method is entirely different, depending more upon mechanical assistance of a non-photographic character in the production of the unlimited number of negatives he uses for producing his printing surfaces, and the results more closely resemble those of chromo-lithography. What particulars Obernetter himself has from time to time communicated are here given. He first produces, by the dusting-on process, as many copies of the original negatives as there are colours to be reproduced. The negative intended to produce the plate from which the blue will be printed is obtained by a long exposure and only slight dusting of the reproduced negative. That intended to reproduce the plate for the non-actinic colours—yellow or brown—should be correctly exposed and dusted in; while that intended for the red should be subjected to a shorter exposure and more vigorous dusting. By retouching, the densities of the various negatives may be modified by strengthening them in parts, other portions are stopped out, and the negatives so manipulated that they will produce plates capable of giving impressions—when printed in their proper colours—giving a facsimile reproduction of the original work. Much will depend upon the artistic qualifications of the operator, who may, by extending the number of plates, finally produce copies of considerable artistic value.

HÖsch, of Munich, has patented a process in which the same result is attained in a somewhat different manner. A negative is produced, and from that a Collotype plate from which a number of impressions are taken equal to the number of printing desired or necessary in the finished chromo-collotype picture. Each print has certain portions painted over in a neutral tint, such portions depending upon the colour of the ink in which it is intended to print the corresponding plate. Other portions are stopped out white in the print, or black in the negative, and from the prints so treated a set of negatives are taken; these are utilised for the production of a set of Collotype plates, which, printed from in suitable colours, yield impressions of great excellence.