238 PEACTICAL PHOTO-MICKOGKAPHY 



the artistic side need not be considered, there are only two 

 in general use : 



1. Printing by daylight on gelatino- or collodio-chloride 

 printing-out paper. 



2. Printing by artificial light on some type of bromide paper. 

 Either of these methods gives a print in which the image 



is on the surface of the paper and not in its depth, so that 

 the maximum amount of detail is brought out. 



The first process is that usually referred to as printing on 

 P.O. P. The paper may be bought of the required size, and is 

 placed in a printing-frame with its sensitive surface in contact 

 with the film-side of the negative. The paper should be placed 

 in position in the frame in a dull light and then placed in bright 

 daylight to print. The time occupied in printing depends on 

 the state of the light, and the time of year, and may vary from 

 half an hour to a day, or even more in winter. 



In cases where printing is greatly prolonged, care should 

 be taken to see that the negative and paper are well protected 

 from damp, as otherwise staining of the negative, which it is 

 practically impossible to remove, may result. The resulting 

 print can be modified to some extent by the brightness of the 

 light in which it is printed. In dealing with a very dense 

 negative it is sometimes permissible to print in direct sunlight ; 

 whereas a very thin negative may be somewhat increased in 

 brilliancy by printing in as weak a light as possible. The 

 printing process should be carried somewhat farther than 

 appears necessary, as considerable reduction of the image 

 occurs in subsequent operations. 



The above operation having been completed, the next 

 thing is to tone the print, thereby altering its colour, which 

 may be ultimately almost any shade from brown-red to 

 blue-black. The toning process is best carried out by the 

 solutions recommended by the makers, and the formulas for 

 these are always enclosed in each packet of printing-paper. 

 Practically, however, all papers of this type may be toned by 

 a solution made up of a 10 % solution of sulphocyanide of 

 ammonium and 1 % solution of chloride of gold. The print 

 is first well washed in several changes of running water until 

 the water ceases to acquire a milky appearance. To 1000 c.c. 

 of water then add 1 c.c. of the sulphocyanide solution, and 



