90 J. Watcrliouse — The Application of ^hotograp'hy [No. 2^ 



but with certain modifications due to the peculiar nature of the printing 

 surface. The principal of these was the use of two inks, one stiff, fo? 

 giving force to the shadows, the other thin, for bringing out the more 

 delicate half tones. 



The ' phototype' process as at first proposed laboured under the defect 

 of not being able to yield a large number of prints from a single plate, but, 

 in 1869, it was improved upon in this respect by Albert, of Munich, ^vho 

 substituted a thick glass plate for the metal plate used by Tessie du Mothay 

 and Marechal as a support for the colloid film. His films consisted of albu- 

 men, gelatine and bichromate of potash alone, and he gave them the required 

 solidity and adherence to the glass by first coating the plate with a 

 sensitive colloid mixture containing a large proportion of albumen, and 

 then giving the under side of this first coating a preliminary exposure 

 to lio-ht through the glass. The second coating containing more gelatine 

 was then applied, and after it had dried, and the photographic image 

 had been impressed upon it, the plate was again exposed from the back, 

 in order to thoroughly solidify and combine the under part of the com- 

 pound film. The gelatine films so prepared were capable of yielding some 

 hundreds, or even, it is said, thousands of perfect copies. This process 

 is still largely used by its inventor and is known by the name of Albert- 

 type.* 



According to some authorities, Messrs. Ohm, Grossmann and Gemoser, 

 of Berlin, took out a patent, in 1867, for a method of photocollographic 

 printing comprising, in addition to the use of glass as the support of the 

 ffelatine film, of the double coating of the plate and of the hardening of the 

 film by exposure of the back surface, the introduction into the sensitive 

 gelatine mixture of certain resinous compounds dissolved in spirit, by which 

 the gelatine film is rendered quite insoluble and admirably adapted to form a 

 fine printing surface. It is said on the other hand that the credit of all these- 

 improvements is due to Albert ; but, in any case, it is certain that until after 

 the publication of Albert's process early in 1869, Ohm and Grossmann's was 

 almost unknown and had not come into general use. In October 1869, the 

 Autotype Company in London acquired the patent, and have since worked 

 the process with the greatest success. 



About a year after the publication of Albert's method, Mr. Ernest 

 Edwards, of London, introduced, under the name of ' Heliotype,' a very im- 

 portant modification of the photocollotype process. 



He first waxed a glass plate and then coated it with a substantial layer 



of gelatine and bichromate of potash, containing a small quantity of chrome 



alum with the object of hardening the gelatine and rendering it insoluble, 



without destroying its impermeability to water. When dry, the gelatine 



* ^ ThotograpMc Nnvs^ Vol. XIII, p. 121. 



