PRINTING PROCESSES 229 



foot from the light, according to the density of the nega- 

 tive, and if very dense may be exposed to diffused day- 

 light for a few seconds. Correct exposure is easily found 

 by exposing a piece of the paper beneath the negative 

 for a time that is judged to be about J or J of the correct 

 time, and then successively covering up i, f , f , -*- of the 

 negative with a card, and continuing the exposure at 

 each step by times which are to the first exposure as 

 1, 2, 4, and 8. On development the paper will be divided 

 into strips which have received exposures which are to 

 each other as 1 : 2 : 4 : 8 : 16, and the correct time can be 

 readily judged for future exposures. The developer is 

 then rapidly poured over the paper in a dish, and develop- 

 ment is complete with gaslight papers in a few seconds, 

 while bromides take 2 to 3 minutes. They are fixed in 

 15% hypo containing 5% potassium meta-bisulphite, and 

 then washed well. 



These three printing processes provide all that is 

 necessary to get the best results from a wide variety of 

 negatives. 



P.O. P. will give the finest detail from good negatives. 



Gaslight paper is most suitable for flat or thin nega- 

 tives, or in any cases where the greatest possible contrast 

 is desirable. 



Bromide paper does not give such contrasty prints as 

 gaslight, and should be chosen for very hard or dense 

 negatives, and is used for enlargements. 



The matt grades of the development papers are more 

 useful than matt P.O. P., because when these papers are 

 chosen the attainment of detail is not as a rule so im- 

 portant. The semi-glossy varieties can be particularly 

 recommended. 



Platinotype and Carbon Processes. The platinotype 

 process is not so much used for photomicrography as its 

 merits might warrant. It suffers in comparison with the 

 others on the score of expense and susceptibility to 



