230 PHOTOMICROGRAPHY 



atmospheric moisture, but with care no other black-and- 

 white prints can compare with platinotype for beauty 

 and permanence. Good negatives are essential, and those 

 grades of paper with the smoothest, almost semi-glossy sur- 

 face are the best : Black Japine Platinotype, for example. 

 The matt varieties do not give such fine detail as P.O. P. 

 The paper is printed-out in daylight until all detail is 

 visible, then developed in potassium oxalate solution, and 

 fixed in dilute hydrochloric acid. 



Carbon printing does not render fine detail very well, 

 and red and brown pigments are worse in this respect 

 than the blacks and blues. Carbon may, however, be 

 very useful in circumstances demanding prints of a 

 definitely selected colour. 



Glazing Prints. Glossy papers are glazed in order to 

 give them the highly polished surface which brings out 

 fine detail to the best advantage. The finished prints 

 are hardened in formalin, given a short wash in water, 

 and squeegeed down while wet on ferrotype sheets or 

 plate glass. The ferrotype sheets are previously rubbed 

 over with waxing solution, and the glass polished with 

 French chalk. 



Enlarging. There are several ways in which enlarg- 

 ing on bromide paper forms a most useful photomicro- 

 graphic process. In certain cases, for instance, it may 

 be impossible to use a high-power objective on account 

 of its small depth of focus, or because its definition breaks 

 down when used with a high eyepiece or long extension. 

 A low-power photomicrograph on enlargement may, 

 under these circumstances, give a much better result 

 than a negative taken directly at a higher power. But 

 it must always be remembered that, if anything, there 

 will be a loss of definition and detail in the enlargement, 

 and that the low-power objective cannot give the same 

 resolution as the high -power. Large prints for demon- 

 stration are also much more cheaply made by enlarge- 



