A. Processes in which the aim is to produce diagrams.
B. Processes in which the aim is to produce pictures.
For the first purpose any of the methods are useful: that is, typographic processes, where the block is set up with the type in the printing-press; the collotype process, where the prints are subsequently mounted on paper, or interleaved in a book; and the photo-etching process, where the plates are introduced between the leaves of a book.
|Diagrammatic plates.|
It is obvious that when the aim is diagrammatic, brilliancy, sharpness, correct drawing, and the truthful rendering of texture are the requisites, as in the reproductions of negatives from nature to illustrate scientific works, books of travel, &c. In such cases these are the main points to be considered; and when to these considerations is added the question of cost of production, it is evident nearly all the processes worth mentioning which are now in existence will serve one or other, or all such purposes. But when the question comes to be considered from an artistic point of view, the matter is totally different, for it is a sine quâ non in this case that all the artistic quality of the original photograph be preserved. |Art blocks.| Cost must not be considered. From the art point of view alone, then, we shall briefly discuss these processes. |Platinotypes.| As we said in a former chapter, of ordinary printing papers the platinotype is alone worth considering for this purpose, but for book illustration a serious objection to its use is its monotony. For, although there are two colours, the charcoal grey and the sepia, the gamut of colour is very limited; a serious matter this, for our experience leads us to believe that there is a particular colour and tint especially suitable to each subject. Another objection to all ordinary printing papers is the want of relief in the gelatine film of an ordinary negative, a want which gives a certain flatness in the resulting print, when compared with a print from a copperplate where the cavi-relievo is deeper. Relief in the block undoubtedly has a great influence on all results, and in all the photo-mechanical processes “depth” is an essential, and the best processes are those in which the printing-plates have the deepest surfaces. Another fact which renders platinotype less valuable than photogravure is that there is always a certain amount of “sinking in” of the image, as there is with a painting on canvas; but a painting can be brought up by varnish, a platinotype cannot.[[13]]
[13]. This “sinking-in” is now scarcely appreciable with, the new cold-bath process.
Let us, then, examine the various processes, and see which will serve our purpose.
Collotypes, Woodbury types, &c. not durable.