1878.] to the Beproduction of Maps and Plans. 85 



280 et seq. The accompanying specimen of a reduction from an old 

 engraved map will give an idea of the results that may be obtained. 



In the Southampton process the whole of the unaltered gelatine is 

 removed from the paper, and the objection has been made that, in con- 

 sequence of this, the ink on the lines being left on ridges of gelatine is 

 more liable to spread in transferring, that the fine lines are liable to be 

 washed away by the dissolution of the gelatine beneath them, and that the 

 prints are liable to slip during transfer. To remedy these defects various 

 methods have been proposed for retaining the gelatine on the paper. 



One of the best of these methods has been perfected by Capt. Abney, 

 who has patented it under the name of ' papyrotype.'* 



A tough paper is coated with gelatine, and subsequently treated with 

 alum or chrome alum. It then receives a coating of gelatine and bichromate 

 of potash as in the Southampton process. After exposure to light the 

 print is drawn through cold water, and is then ' squeegeed' down on to a 

 smooth metal plate, and inked in with a soft gelatine roller charged with 

 transfer ink. The ink ' takes' only on the parts exposed to light, while the 

 ground of the print remains clear. When the image is fully inked up, the • 

 print is dried and exposed to light, to harden the gelatine thoroughly by 

 the action of light on the bichromate salt still remaining, and is then ready 

 for transfer to stone or zinc. 



Among the advantages claimed for this process, the principal are that — 



The ink which forms the lines is not left on ridges of gelatine, as in 

 the Southampton method. The fine lines are not liable to be removed. 

 The surface of the transfer will have no tendency to slip during transfer. 



In practice this method was not found to answer in this country so 

 well as the ordinary one, but a modification of the latter has lately been 

 introduced in the Surveyor General's Office, with the same object as the 

 papyrotype, and seems to answer well. 



The paper is prepared as usual with two coats of gelatine and bichro- 

 mate of potash. It is then put away for a few days, in order to allow the 

 gelatine to become hard and insoluble. When required for use, it is 

 coated again with a mixture of gelatine and bichromate of potash of about 

 one-third the usual strength, and is then exposed to light and inked in the 

 usual way. The washing is done with cold water instead of with hot. 



Instead of allowing the gelatine to harden by keeping, which takes from 

 3 to 12 or 14 days according to the season, the hardening action may be 

 hastened by laying the sensitive paper face downwards on a board, and 

 allowing the light to act on the back surface for a minute or two. This may 

 be done, either after the print has been obtained from the negative, or just 



* ^ Listruction in Thotographij^' p. 155. 



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