1878.] to the Reproduction of Maps and Plans. 79 



contact, all intervening air being driven out by means of an india-rubber 

 scraper, or ' squeegee', which also removes all superfluous moisture. The 

 prints and support are allowed to remain together for a short time, and are 

 then immersed in wai^m water. After a little while the soluble gelatine will 

 soften and become partially dissolved, when the paper forming the original 

 support of the layer of gelatine may be gently removed, leaving a dark 

 slimy-looking mass on the transfer paper. The soluble gelatine gradually 

 clears away by the action of the hot water and reveals the image in more or 

 less perfection of details according as the exposure has been properly timed. 

 When fully developed, the print is washed with cold water, then passed 

 through a solution of alum, rinsed again with water and allowed to dry. 



Instead of paper, any other suitable permanent support may be used, 

 but whatever the support may be, a reversed negative must be used if it 

 is desired to obtain non-inverted j^ictures by the single transfer method. 



When it is inconvenient to use a reversed negative, and it is desired to 

 obtain a non-inverted picture — the development of the tissue-prints must 

 be conducted by the double transfer method upon a temporary support, 

 either rigid or flexible. The discovery that the pigment pictures might be 

 developed upon any impermeable surface is due to Mr. J. R. Johnson, who 

 also found that if such surface previously receive a coating of some fatty 

 or resinous compound, the picture may be transferred, after development, to 

 a final support. 



The most suitable surface for the temporary support is a sheet of zinc, 

 which may be either polished or grained ; opal glass, or porcelain plates may 

 also be used with advantage. 



The plate emj)loyed as the temporary support first receives a coating 

 of a solution of wax and resin in turpentine, and some operators coat the 

 plate with collodion after the waxing, in order to improve the surface. The 

 pigment tissue carrying the image is attached to the support under water 

 in much the same way as in the single transfer method, and after remaining 

 for a time, is developed in the same way and allowed to dry. The plate 

 with the picture on it is then rinsed in water, and a piece of what is called 

 double transfer paper — a fine paper coated with an enamel surface — having 

 been soaked in water till quite soft, is laid on the wet plate, avoiding 

 air-bubbles, and pressed into perfect contact with it by means of the india- 

 rubber scraper. The pictm-e with the transfer paper attached is now dried 

 carefully, and when dry separates of itself from the temporary support. 



Mr. J. II. Sawyer of the Autotype Company has introduced a flexible 

 support, consisting of paper coated with a solution of gelatine rendered in- 

 soluble with chrome alum. When dry this is coated again with an alkaline 

 solution of shellac, dried and well rolled under powerful pressure — it is 

 afterwards coated with a waxing compound. The use of this flexible sup- 



