Transparency painting will no doubt be one of these methods. The artist will paint on a set of sheets of transparent celluloid or glass, mounted in frames of wood and hinged so that they can, for purposes of observation, be put aside and yet brought back to their original positions quite accurately. Each different transparent sheet will be intended for one pure colour, the only pigments used being of the most transparent description obtainable.
The picture may thus be built up by successive additions and alterations, not all put upon one surface, but constituting a number of "monochromes," superimposed one upon the other. When finished, each of these one-colour transparencies can then be reproduced by photo-mechanical means for multi-colour printing in the press.
By what are known as the photographic "interruption" processes, a kind of converse method has achieved a certain degree of success. A landscape or a picture is photographed several times from exactly the same position, but on each occasion it is taken through a screen of a different coloured glass, which is intended for the purpose of intercepting all the rays of light, except those of one particular tint. Coloured prints in transparent gelatine or other suitable medium are then made from the various negatives, each in its appropriate tint; and when all are placed together and viewed through transmitted light, the effect of the picture, with all its colours combined, is fairly well produced. More serviceable from the artistic point of view will be the method according to which the artist makes his picture by transmitted light, but the finished printed product is seen on paper, because this latter lends itself to the finest work of the artistic printer.
The principal branch of the work of the photographer must continue to be portraiture. He cannot greatly reduce the cost of getting a really good negative, because so much hand-labour is required for the task of "retouching"; but he can give, perhaps, a hundred prints for the price which he now charges for a dozen, and make money by the enterprise. It has already been proved that there is no necessity for using expensive salts of gold, silver or platinum in order to secure the most artistic prints; and, as a matter of fact, some of the finest art work in the photography of the past quarter of a century has been accomplished with the cheapest of materials, such as gelatine, glue and lampblack.