As it has become customary to illustrate costly 'books by means of large photogravure plates. so it has become usual to employ living artists of celebrity to make original monochrome pictures :i for t'll reproduction. These are sometimes pro duced in the more usual fashion by means of water-color work in bistre, sepia, India ink, or other one-colored pigment, but they are also made on a very large scale by oil painting upon can vas, exactly as in the case of paintings intended for exhibition or sale, except that they are worked in such gray or brownish-gray pigment as the painter and the photographer agree unon as convenient for the one and most easily adapted to the work of the other. Such monochrome paintings are often of considerable importance. and those collectors of works of art who have purchased them at the time of their production • have considered them an important part of their possessions. It may be stated, also, that the im provements made in orthochromatic have made it possible to obtain very accurately the relative color values of the most difficult sub jects, elaborate oil paintings, and the like.
The difficulty with the employment of photo gravure in book work is the great cost, not alone in the production of the plates f for it is not un common to take two or three months in the per fection of a large plate), but of the printing.
which has to be done on a hand press. and slowly, so that every separate impression. of which fifty may be bound up in a folio volume, will have cost a definite sum of money over and above the cost of the plates. It is on this ac count that modified processes are continually brought forward intended to produce plates from which the printing may he done more rapidly. There is, however, always the difficulty in print ing from intaglio-engraving. that in order that the paper shall take the ink from the ineised lines perfectly, leaving none behind. so that the design is reproduced in every minute particular by the raised pattern of ink on the paper, only a slow and painstaking process will serve.
A kind of photogravure has been introduced in which a screen is employed to make the grain exactly as in the case of the half-tone process described below. This. of course, if perfected, will tend toward much greater ease in rapid printing.