356 PHOTOGRAPHIC FACTS AND FORMULAS 
glycerine and water plus 2 per cent of ordinary salt may be 
used. 
PHOTOGRAVURE.—Negatives should be full of detail and 
without hardness and preferably carbon transparencies 
should be made, showing all details in the high lights, with- 
out great density. The thinner these are kept, providing 
details in the high lights are visible, the better. Special 
transparency tissue is issued by the makers, or standard 
brown may be used. 
Cleaning the Copper Plate. Rub over with 5 per cent solu- 
tion of potassium carbonate with cotton swab, rinse well and 
treat in the same way with 5 per cent solution of sulphuric 
acid. Wash well and polish with whiting made into paste 
with 3 per cent solution of ammonia. Rinse plate with hot 
water and dry with clean cloth. 
Graining the Plate. The usual dusting boxes should be 
used and the longer the time between setting the powdered 
asphalt in motion and the insertion of the plate the finer the 
grain. For a coarse grain wait for 20 seconds. Allow the 
plate to remain for from 2 to 5 minutes. For very fine grain 
it may be necessary to shake box and grain two or three times. 
Resin may be used but does not give such good results in 
unskilled hands. 
Setting the Grain. Grip the edge of the plate with a hand 
vice, using card to protect the copper, and heat over a gas 
flame, with continual movement so as to even the heat, until 
a steel blue colour shows. 
Mounting Resist. Place the grained plate in water at 21° 
C. (70° F.), slip in the tissue and brush the face with a soft 
brush to remove air bubbles. Bring the two into contact and 
lift from the water, squeegee well, and place between blotters 
for 10 minutes. Develop with water at 38° C. (100° F.) or 
if underexposed raise temperature to 49° C. (120° F.). 
