PROCESSES IN ILLUSTRATIONS 157 



the colours are employed, or in extreme cases colour filters are 

 used to lessen the importance of the predominant one. 



The ruling of the screen used in making the original nega- 

 tive is of importance. In ordinary newspaper illustrations the 

 lines run 60 to the inch, in magazines they run 133 or 150 to 

 the inch. The finest screen in general use is 175 to the inch. 

 It would be impossible to print from a block with such fine dots 

 as these on any ordinary paper, as the result would be a blur. 

 A specially smooth surface is required : this can only be obtained 

 by the use of paper which has been faced with china clay paste 

 by being passed through a bath of the material and rubbed in by 

 metal brushes to attain a high polish. As a result, not only is 

 the eye wounded by the glistening smoothness of the paper on 

 which the illustration is printed, but there is a certainty that 

 the paper will fall to pieces in a comparatively short number of 

 years, as some of the earliest specimens of it have already done. 



The question of the proper illustration of a book is largely 

 a question of expense. From every point of view it is better 

 that the illustrations should form part of the book itself, and not 

 be inserted later. The process of insertion brings an added 

 cost ; there is always a risk of loss of the inserted plate ; it is 

 usually inharmonious with the body of the work ; it is, in short, 

 an excrescence on it. The ideal illustration for a printed book 

 is a wood engraving, whose capabilities in skilled hands are 

 hardly to be over-estimated ; and a line block can be printed 

 with the text in a very satisfactory way, but all other pro- 

 cesses require separate printing. The objection to the half-tone 

 process — that it destroys the unity and durability of the book- 

 is one that has not been overcome, and promises to cause its 

 supersession. 



The expense of an ordinary half-tone block from a coloured 

 original varies, of course, with the amount of work put into it — 

 say from 5^. to gd. per square inch, with a minimum charge for 

 12 square inches. When there is much cutting away to be done, 

 the minimum cost would be much higher. 



Collotype 



Collotype or phototype is a very satisfactory process of 

 reproduction of which examples are familiar to every one in the 

 best picture postcards. The preliminary expense of their repro- 

 duction is small. A rough film is spread upon glass, and on 



