Page 661 the smooth sheet 7131 



sheet must be complete without the necessity of reference to the ahiminum sheet which 

 is not a part of the permanent records. The smooth sheet itself, however, mugt not 

 be plotted on aluminum. 



7131. Grained Aluminum Sheets 



The maximum size of aluminum sheets available at the Washington Office is 38 by 

 54 inches and they are all 0.02 inch thick. This size or smaller can be furnished either 

 grained, painted, or mounted with drawing paper. A sheet of maximum size costs 

 about $2.50 and the cost of graining is approximately 60 cents per sheet. 



The grained surface of an aluminum plate will take either pencil or ink, but the 

 abrasive nature of the surface wears a pencil point down so rapidly that it is difficulty 

 if not impossible, to draw fine lines with a pencil sharpened to a chisel point. Soft 

 pencil marks can be removed with art gum. A hard eraser should not be used since it 

 removes the grain and once this has occurred neither ink nor pencil marks can be made 

 on that portion, unless it is subsequently roughened with a snake slip. Ink 

 can be removed from the grained surface by the use of water or a dilute solution of oxalic 

 acid (1 ounce oxalic acid crystals to 15 ounces of water). A slight stain will remain 

 which can be removed by the use of a snake slip. 



Used aluminum plates need not be returned to the Washington Office. 



7132. Painted Aluminum Sheets 



Painted aluminum sheets arc similar to the above, except that, instead of being 

 grained, the drawing surface is provided by spraying the aluminum with enamel paint. 

 The plates are generally given three or four coats of the enamel, applied in the same 

 manner as is the finish on automobile bodies. 



Both ink and pencil work can be done on painted aluminum sheets although with 

 not the same facility as on a good grade of drawing paper. 



7133. Mounted Aluminum Sheets 



Drawing paper mounted on aluminum sheets is the most satisfactory solution of 

 the distortion problem if the sheets are not unduly exposed to moisture. The paper 

 must be mounted on both sides of the aluminum regardless of whether one or both sides 

 are to be used; otherwise the paper will contract or expand and so warp the aluminum 

 sheet that it will not lie flat. Mounted aluminum sheets are prepared in the Washing- 

 ton Office and any make of unmounted drawing paper can be used. The kinds ordi- 

 narily used are chart paper or two-ply Bristol board, depending on the purpose for which 

 they are intended. (See also 233.) 



In mounting, the paper is applied to the two sides, one at a time, with a high quality 

 lithographic paste, sparingly used and avoiding excessive moisture, as the latter has a 

 tendency to make the paper surface porous or mushy which ruins the fine drawing quality 

 of the paper. One of the requirements for successful mounting is that the paper must 

 be bonded to the aluminum under considerable pressure, this pressure being more impor- 

 tant than the quality of the paste. 



Some difficulty has been encountered with the moisture in the paste oxidizing the 

 aluminum and causing blisters to form at some future time. Of course this is no draw- 

 back if the sheet is being prepared for immediate temporary use. This difficulty can 

 be overcome in various ways, one of the most successful of which is coating the aluminum 

 with shellac before mounting. 



