276 PHOTOGRAPHIC FACTS AND FORMULAS 
Allow to soak for 15 minutes, dissolve by heat, and add: 
Oxalic acid, pure 2.0 2 24 gr. 
There will be further required a 10 per cent solution of 
sodium platinum chloride (NaC1),.PtC1,.6H,O, and a 1 in 6 
solution of potassium chloroplatinite. All stock solutions 
must be kept in the dark. 
The best results are obtained with pure linen papers; cheap 
wood-pulp papers will not give good results. While it is not 
absolutely essential with good papers, a preliminary sizing 
is desirable, and for this purpose gelatine, arrowroot, or 
tragacanth may be used. The disadvantage of gelatine is 
that it is very prone to form air bubbles, and arrowroot is 
preferable. To prepare the gelatine size, make a 2 per cent 
solution of gelatine in water, and add 1 per cent of alum. To 
make the arrowroot rub 20 g (154 gr.) into a thin cream with 
water, add to 1000 ccm (16 0z.) boiling water with constant 
stirring, and continue boiling for 5 minutes. Allow to cool, 
and remove the skin which forms on top. The gelatine size 
must be used warm. 
To apply the size, the paper should be pinned to a drawing 
board, or other flat surface at the corners and the size applied 
with a broad flat brush in straight strokes, first across and 
then up and down the paper, until the surface is uniformly 
wet. Then a round soft brush, a perfectly clean shaving 
brush being excellent, should be worked all over the surface 
until it appears even and begins to lose its gloss. It may 
then be hung up to dry. For rough drawing papers the sheets 
should be immersed in the size for from 5 to 30 minutes, 
according to the thickness of the paper, and the roughness 
of the surface. The paper should be drawn over the edge of 
the dish, so as to wipe off as much solution as possible, and 
then hung up to dry with the end that leaves the dish last at 
the top. 
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