488 HANDBOOK OF PHOTOGRAPHY 



on the hairs in the blending process, it is advisable to reinforce the setting of the 

 blender, using a thinned Duco cement in the manner described in the section on 

 Platinum Printing. 



The brushes should be thoroughly washed in cold water as soon as the coating 

 operation is completed, for, if the coating mixture is allowed to dry in them and is 

 exposed to light, it will be impossible to remove it. They should be hung up to dry, 

 bristles down, so that they may keep their shape. 



The Pigments. — -These must be either water-color paints or dry-powder colors, the 

 former being preferable; oil colors will not do, and though some authors recommended 

 tempera colors, the present writer has not found them satisfactory. They must be the 

 so-called "earth pigments," such as lampblack. Ivory Black, burnt umber, burnt siena, 

 Venetian red, Prussian blue, cobalt blue, cadmium orange, cadmium yellow, etc.; the 

 aniline colors will not do. It is better to buy a good grade of water-color tubes; the 

 powder colors are much cheaper, but they must be ground for use, and the time thus 

 consumed amounts to more than the money saved. 



It is immaterial what manufacturer of colors is favored; the pigments of Talens & 

 Son, Winsor & Newton, Devoe & Reynolds, or, in fact, any standard maker can be 

 relied on; the writer prefers those of Talens, but this is partly the result of habit and 

 partly because that firm puts up an excellent black, known as Photo Engraver's 

 Black, which is much cheaper than the ordinary water colors. The selection of colors 

 given above will be ample for any ordinary use; as a matter of fact, three or four tubes 

 are plenty to start with — say. Ivory JBlack for a neutral black and burnt umber or 

 Venetian red to warm it up, with cobalt blue for cool blacks. 



Whatever make of pigments is used, the same one should be adhered to throughout, 

 since the pigment will be measured by the number of inches squeezed from the tube, 

 and the apertures of the tubes vary with different makers. 



The. Gum. Solution. — This is a fairly thick solution of gum arable in water, and, as 

 different samples of gum vary, it is well to use that of one single maker; even so, there 

 will be some variation between lots. It should be granular, not in the form of tears 

 or powdered, as the first is easiest to dissolve. The writer favors McKesson & Robbins 

 Gum Acacia No. 1 Granular, but this again is a matter of habit; an equivalent article 

 from any good maker will be satisfactory. 



Some preservative will be necessary, for, although a sour gum solution works as well 

 as a fresh one, it works differently, and the progressive souring will throw the worker's 

 calculations out. Formaldehyde and carbolic acid are unsuitable for this purpose, 

 and, though oil of cloves is sometimes recommended, the writer prefers bichloride of 

 mercury, which, as noted in the section on Platinum Printing, is a dangerous poison 

 and should be used with care. It is, however, an efficient preservative; the writer has 

 known a gum solution so treated to remain perfectly fresh for 18 years. 



The formula which is preferred by the writer, and on which subsequent formulas 

 will be based, is as follows: 



Water 3000.0 cc. 32 oz. 



Gum arable (granular) 500 . g. 1 lb. 



Mercuric chloride 6 . g. 90 gr. 



The gum is most conveniently dissolved by rubbing it up in a mortar, a little at a 

 time, with portions of the water. The preservative may be rubbed in at any stage of 

 the proceedings but should be thoroughly stirred through the final solution. This 

 manner of dissolving the gum is tedious but is more satisfactory than the method 

 sometimes recommended, of putting the gum into a bag and suspending it in the water; 

 if the latter plan is used, the gum coagulates into a mass which requires a very long 

 time to go into solution. 



