656 HANDBOOK OF PHOTOGRAPHY 



reversal will be complete in about 2 or 3 min. ; the plate should be washed in running 

 water for another 2 or 3 min. and then immersed again in the developer and left there 

 until the remaining emulsion is completely blackened. The plate should now be 

 given a final wash in running water and placed to dry. 



Varnishing the emulsion of the plate with a 3 per cent solution of gum dammar in 

 benzol is recommended. The varnishing should be done by pouring a small quantity 

 in one corner and then gradually tilting the plate to allow the varnish to flow through- 

 out the surface, after which the surplus varnish can be drained back into the bottle. 



The brilliancy of a color plate can be increased bj^ intensification, and for this 

 purpose the Agfa mercury intensifier put up for the purpose will be found very con- 

 venient. Intensification, of course, should be done before varnishing the emulsion 

 of the plate. 



If the original exposure of a color plate has been too great, the final result will be 

 a thin positive after the reversal, and conversely, if not enough exposure was given 

 originally, the final positive will be very dark. In the previous case some correction 

 can be obtained by the intensification method already described, while in the latter 

 case, some kind of compromise could be obtained by reducing chemically the final 

 positive. In general, however, the reduction of the color plate does not lead to suc- 

 cessful results, and it is best to control the original exposure by correctly measuring 

 the light value by means of an exposure meter. 



Lumiere Auiochrome Plates and Filmcolor. — The Lumiere Autochrome plates and 

 Filmcolor can be processed in the same, type of developer and reversal bath as recom- 

 mended for the Agfa color plate. 



The manufacturers, however, recommend the following developer as the most 

 suitable : 



Distilled water 1000 cc. 



Metoquinone (quinomet) log. 



Sodium sulphite (dry) 100 g. 



Ammonia (sp. gr. 22° Baum6) 32 cc. 



Potassium bromide 16 g. 



For second development it is recommended to use an Amidol developer of the 

 following composition : 



Water 50 cc. 



Sodium sulphite (dry) 1500 g. 



Amidol (Dinol) 2^2- 



Intensification can be carried out with mercury intensifier. The Lumiere Auto- 

 chrome plate also can be varnished with gum dammar as described previously, 

 although this is not necessary with color film. 



It is possible to make color-separation negatives from Agfa color plates as well as 

 from Lumiere color plates and film, and for the purpose very sharp filters should be 

 used. The most suitable are the Wratten filter Nos. 29, 61, and 50. In general, how- 

 ever, the results obtainable by using color screen plates and film as originals do not 

 approach in the least the results obtainable by making color-separation negatives 

 directly from the original subject. 



Dufaycolor Film. — Of late Dufaycolor film has come into prominent use. This 

 film is made up essentially in the same manner as the Lumiere Filmcolor with the 

 exception of the color-filter elements which consist of a geometric pattern of small 

 squares of the three primary colors, upon which is the regular panchromatic emulsion. 



In the same way as the color-screen material previously described, the Dufaycolor 

 film requires special compensating filters when the exposure is made with various 



