542 PKOCEEDINGS OF SECTION I. 



and chemical affinity. This process is carried on by the Autotype 

 Company in London. Their reproductions may be taken from 

 any photograph engraving or printing in monochrome. 



Callotype printing claims to be the latest and most promising 

 invention, bearing as it does a closer relation to both lithographic 

 and relief printing. 



The pictures by this process are printed from gelatine surfaces? 

 which one would think most unlikely to stand the wear and tear 

 of a machine. Now, gelatine soaked in cold water swells up — in 

 hot water it dissolves — if gelatine is mixed with bromide of 

 potassium and exposed to the light it becomes brown in colour. 

 What is strange and curious about this material is, that the 

 exposure to light robs it of its property of swelling in water. 

 Further, it becomes of an apparently greasy character — water 

 will not mix with it. Now if we print on a piece of paper coated 

 with bichromatised gelatine and put it in water, the exposed part 

 will not swell, nor will it absorb water. The unexposed parts on 

 the other hand will swell as ordinary gelatine, the swollen parts 

 will not mix with fatty printing ink, but the unswollen parts 

 will readily receive it, and here is the basis of the collotype 

 process. 



Briefly, it is this — a glass plate or a metal plate may be coated 

 with a uniform layer of bi-chromated gelatine, and this is exposed 

 to light under a negative. Certain parts become quite insoluble 

 by the action of light, others remain soluble and capable of 

 absorbing water. 



The plate is damped and a roller charged with fatty ink is 

 passed over it. Those parts which refuse the water refuse the ink ; 

 and a piece of paper being applied with pressure the ink sets off 

 on the paper forming a print; but more than this occurs, as we 

 have an infinite number of grades between the two extremes of 

 water-taking and of ink-taking parts. Those parts which had 

 but a slight exposure to light, being capable of receiving both ink 

 and water, the proportion in which each is received depending on 

 the extent to which the part has been acted upon by the light. 



Under exposure in a photo-printing frame the gelatine coating 

 turns from an even yellow to a faint brown. It is then soaked, 

 during which the exposed parts become reticulated or grained. 

 Before being used, the plate is soaked in water and then it is 

 laid on the bed of a machine or press and is rolled up with an 

 ordinary lithographic roller and printed in the usual way. 



The progress of callotype printing will be greatly influenced by 

 the fact that the machines can be adapted readily to any ordinary 

 lithographic or letterpress machines, and by the simplicity of the 

 process and ease with wliich a printer may, by the aid of a camera 

 and a few chemicals and plates, make his own surface and produce 

 Iiis illustrations without the services of artist or engraver. 



