ELEMENTARY PHOTO-MICROGRAPHY. 89 



tube are further protected by a wide rubber band. 

 Thus protected, the paper will keep in good con- 

 dition many months. The lemon-coloured surface 

 of platinum paper is more sensitive to light than 

 is that of P.O. P. ; consequently, the placing of 

 the paper in the frames, the examination of prints, 

 and development must be done in dull light. After 

 the sheet of platinotype paper is put on the nega- 

 tive, it is desirable, though not essential, to add a 

 protecting sheet of rubber or waterproof paper 

 before fastening the back of the printing frame. 

 During exposure, which must be by daylight, an 

 occasional peep at the paper will show how far 

 printing has proceeded. The image is only faint 

 grey when finished, but every detail should be 

 seen, however feeble. If there be any part of the 

 print that should be pure white when finished, the 

 attention should be fixed on that spot, and its tint 

 compared with that of the edges of paper. So long 

 as this is the same lemon colour, it may be gathered 

 that printing is not carried too far. As develop- 

 ment is very rapid, the exposure must be correct 

 to get good results. After a few trials it will not 

 be found at all difficult to determine when to stop 

 printing. The developing bath, which should not 

 be below 60 F., is made up of 



Neutral potassium oxalate . . i ounce. 



Oxalic acid (saturated solution) 



i part to 20 parts of developer. 



Water . . 10 ounces. 



