THE PRODUCTION OF POSITIVES. 155 



with lamp light, owing to the variations in density 

 of different negatives,, an approximation only is pos- 

 sible. At the same time an over-exposed negative 

 always gives the best results, as a weak light and 

 under-exposure is all that is necessary for the pro- 

 duction of a good positive. We have found fifteen 

 seconds, three feet from an ordinary paraffin lamp, 

 sufficient exposure for a negative possessing the 

 characteristics recommended in a former chapter. 

 When no other means of printing but by contact 

 are available, a denser negative would give better re- 

 sults. 



Copying with the camera is to be preferred to 

 direct printing ; first, because the exposure is length- 

 ened ; and secondly, because the character of the 

 resulting picture depends more on the size of the 

 stop, and intensity of the illumination than on the 

 density of the negative, and as a micro-negative is 

 less dense than an ordinary negative, greater power 

 of modifying the positive is placed in the hands of 

 the operator. 



Any form of doublet may be used. The ordinary 

 Petzval portrait combination is to be preferred. It 

 should be capable of taking a cabinet picture. 



A quarter plate negative is the most convenient 

 to copy from, especially for enlarging, because 

 the pictures, produced by a combination cover- 

 ing that sized plate, are more perfect in detail, and 

 when artificial light is employed, it is possible to 

 obtain good illumination without the use of very 

 large condensers or equally large photographic com- 



