490 HANDBOOK OF PHOTOGRAPHY 



these pigments in the proportion of 2 to 1, it follows that the worker will use 1 in. of 

 the black, 3^2 in- of the burnt umber, and 7 drams of the giim solution,, 



Note that no sensitizer is used in these determinations. 



It maj' seem that this method of determination involves a great deal of work, but 

 actually the labor is not excessive, and, if the experiments indicated are carried out 

 and the suggested table is drawn up, a vast amount of effort- and disappointment will 

 in the long run be saved. 



The complete mixture hiust be dilute enough to spread to a sufficient, but not 

 excessive, thickness on the paper. Only the worker's own experience can indicate 

 this characteristic, as it varies with different samples of gum arable and with different 

 papers, a rough paper admitting of thicker coating than a smooth one. If the coating 

 is too thin, an excessive number of printings will be required to secure depth and 

 scale; if it is too thick, it will flake off instead of developing smoothly. A suggested 

 formula which the writer has used successfully with Whatman Cold Pressed Medium 

 follows. It must be borne in mind, however, that this is no more than a suggestion, 

 put forward as a basis for the reader's own experiments. 



Talens Photo Engraver's Black 25 . mm. 1 in. 



Gum solution 15.0 cc. 4 drams 



Sensitizer 35 . cc. 10 drams 



The pigment is squeezed from the tube into a mortar, is well rubbed up with the gum, 

 and the sensitizer is added and stirred in. The mixture is then ready to be spread on 

 the paper. 



Coating the Paper. — This operation is like driving a golf ball or sawing a board, in 

 that it can be described and instructions can be given for doing it, but only experience 

 makes it possible for the worker to accomplish it properly; a certain manual deftness or 

 knack is required, and this comes only with practice. 



The paper, which should be cut 2 in. or so larger all around than the finished print, 

 is to be is pinned face up on a smooth board, using — most conveniently— pushpins 

 at the four corners. The coating brush is dipped into the mixture, it is lightly pressed 

 out against the side of the mortar, and the mixture is brushed rapidly back and forth 

 over the paper until the surface is well coated. Then the blending brush is taken up 

 and is drawn lightly but rapidly back and forth over the paper, both crosswise and up 

 and down. It will be found that the brush marks left in coating are smoothed out, 

 eventualh^ disappearing altogether as the gum sets. As the gum sets, the action of the 

 blender becomes gradually lighter and more of a whipping than of a dragging motion, 

 and it should be stopped at just the right point. If it is arrested too soon, the gum will 

 run together in tinj^ puddles, and if it is continued too long, the coating will be streaked. 

 A slight puddling or streaking does no harm, since it tends to blend out to smoothness 

 while the paper is hanging up to dry. 



If several sheets of paper are coated at one time, it will probably be found that the 

 blender becomes clogged with the mixture; it should then be well rinsed in running 

 water and dried by rolling the handle rapidly between the palms of the hands, when 

 its use may be continued at once. 



The commonest fault in coating gum paper is that the beginner tries to get the 

 coating mixture on too thick. The coated paper should not look black but should be 

 of a light greenish gray. 



If the blending has been carried on too long or if the paper buckles so that it is 

 difficult to blend evenly, a uniform coating may be obtained bj^ using the blender with 

 a stippling action. This renders the coating spotty, but most of the spots will blend 

 out as the paper dries, and the others will disappear during development. 



All the above operations can be carried out in an ordinary room, since the coating 

 is not sensitive to light until dry; but the coated paper should be dried in the dark. In 



