SPECIAL PRINTING PROCESSES 487 



Advantages. — If the paper and the pigments are correctly chosen, the prints are 

 absolutely permanent. 



Almost any color or texture of support may be used. 



Almost any color or combination of colors of pigment may be used. 



Modifications of total contrast are very easily made. 



It is extremely easy to make modifications of local values. 



Multiple gum printing offers a longer scale of gradation than any other printing 

 medium. 



Extremely rich blacks may readily be obtained. 



It is commonly believed that gum printing is suitable onlj^ when very broad effects 

 are desired, but this is far from true. By the proper selection of paper as fine detail 

 may be obtained as on a medium rough bromide or chloride paper, though not so fine 

 as on a glossy or semimatte surface. 



Gum is the cheapest of all printing mediums. 



Disadvantages. — ^Like most of the quality mediums, gum is suitable only for contact 

 printing, as it requires almost as strong a light as carbon or platinum. Hence it 

 follows that for large prints, an enlarged negative is required. 



It is somewhat laborious to handle. 



We will now consider the actual working of the process. 



The Negative. — The ideal negative for gum printing is one which has so short a 

 scale of gradation that it can be fuUj^ rendered in one printing of gum. Additional 

 printings are used merely to add weight and contrast. However, this is by no means 

 imperative. By multiple printing and varying the times of exposure so as to register 

 successively the high lights, half tones, and shadows, it is possible to render satis- 

 factorily a negative of practically any degree of contrast. In fact in this respect 

 multiple gum is far more flexible than any other printing medium. 



As is the case with other printing mediums, for a given degree of contrast a thin 

 negative is preferable to a dense one. This holds good with gum to an even greater 

 degree than with platinum, carbon, or Fresson, so on all accounts it is desirable that a 

 negative which is to be used for gum printing have full exposure and brief development. 



The Paper. — This must be a stock which will stand prolonged soaking in cold water, 

 and it must have a slight tooth or grain. As may be inferred from the sketch and 

 from the accompanying remarks, it is practically impossible to make a gum print on a 

 very smooth surface, since the insoluble layer of gum must have slight irregularities to 

 which it can adhere. A print on a perfectly smooth paper will be merely a silhouette, 

 only those portions of the film adhering which have been printed clear through the 

 emulsion. A print on a smooth surface can, it is true, be made by stippling the gum 

 emulsion while it is still tacky, in the process of coating the paper, but the results are 

 not satisfactory. It is not necessary, however, to use a very rough paper; the texture 

 of the ordinary sketch pads which are sold in art stores is rough enough. If desired, 

 for broad effects, almost any degree of roughness is admissible; the writer has made 

 excellent prints on Whatman Cold Pressed Rough, though such exceedingly rough 

 papers are seldom suitable for prints smaller than 11 by 14 in. In general, the writer 

 prefers Whatman Cold Pressed Medium or Michallet Charcoal for prints 11 by 14 or 

 8 by 10 in. and for smaller ones either Michallet Charcoal, Strathmore Charcoal, or 

 some of the ordinary drawing papers which are sold for use by artists and 

 draftsmen. 



In the interests of permanence, the paper chosen should be a good linen stock. 



The Brushes. — Two will be required, a fiat, soft paintbrush about 3 in. wide, set in 

 rubber, for coating; and a flat badger blender about 5 or 6 in. wide for blending. This 

 latter brush is rather expensive, costing about $5 or $6, but it lasts indefinitely; the 

 writer has been using his present one for about 27 j'^ears. As there is considerable drag 



