714 HYDROGRAPHIC MANUAL PaGE 662 



714. Tracing Mediums 



7141. Tracing Cloth 



Tracing cloth is a fine semitransparent linen or cotton cloth, sized on one side, and 

 dull on the other. The best grade is free from pinholes. Because starch is used in its 

 preparation, water will ruin and spot the surface, the spots showing on any reproduc- 

 tions. Wlien working with tracing cloth, the portion not being used should be protected 

 from perspiration by a sheet of paper. 



The dull side of the tracing cloth should be used for all work because it takes ink 

 better. Inking on tracing cloth is facilitated by dusting with talc or pounce, rubbing 

 lightly with a cloth to remove traces of grease which prevent the flow of ink from the 

 pen. 



Tracing cloth distorts considerably more with age and climatic changes than trac- 

 ing paper and therefore should not be used where a minimum of distortion is required. 

 The best grade of cloth is not as transparent as a good grade of tracing paper. 



The most satisfactory tracing cloth on the market in 1942 is "Micro-Weave," 

 fabricated by Holliston Alills Company. It is made in 10- and 20-yard rolls in almost 

 any width desired, and in rectangular sheets in a number of sizes from 19 by 24 inches 

 to 41 by 59 inches. The sheet form is available on the General Schedule of Sup- 

 plies, but the roll form is not. An inferior grade of cloth in 24-yard rolls can be furnished 

 from the Schedule in widths of 30, 36, and 42 inches. This grade is suitable for use in 

 protecting the smooth sheet during plotting (see 761). 



7142. Tracing Paper 



Tracing paper (or vellum) is a thin tough semitransparent paper suitable for 

 making tracings of drawings, or for miscellaneous use where permanence is not im- 

 portant or where pencil work is sufficient. The best quality is odorless, white, 100 

 percent rag, with a high degree of transparency and smooth surface, the texture per- 

 mitting erasures without damage to the paper. 



The best tracing paper, not available in 1942 because of the war, is foreign made 

 under the trade name "Doric" and is marketed by Keuffel & Esser Company, New York. 

 It is usually obtained in 20-yard rolls in widths of 30, 36, and 42 inches. Substitutes 

 must be selected with care as there are many inferior grades on the market. Post's 

 No. 173, fabricated by Frederick Post Company, Chicago, Illinois, is satisfactory for 

 all except the most critical work. 



7143. Cellulose Acetate 



Transparent cellulose acetate sheeting (better known under the more familiar 

 trade name "Celluloid") is useful either as a tracing medium or as a transparent cover 

 for smooth sheets, maps, charts, etc. Cellulose nitrate sheeting must not be used 

 since it is highly flammable and its presence creates a definite fire hazard. Cellulose 

 acetate on the other hand burns at about the same rate that paper does. 



The sheeting is used in two gi^ades: (1) low shrinkage grade, for work requiring 

 a minimum of distortion, and (2) ordinary grade, for purposes in which dimensional 

 changes are not important. 



