73 HYDROGRAPHIC MANUAL PaGE 666 



Errors are occasionally made which must be corrected, and temporary notes or lines are 

 placed on the sheet which must be removed. These erasures as well as the cleaning 

 of the sheet require extreme care in order to avoid damaging the surface of the paper. 



Most temporary pencil lines and notes, if made lightly with a 3H or 4H pencil, can 

 be removed with an art gum eraser without damage to the paper. Penciled errors and 

 the badly smudged places generally require the careful use of a soft red eraser of the 

 "Ruby" or ''Venus" type now on the General Schedule. Ink erasures cannot be made 

 without some damage to the surface, but less damage is generally caused with the skill- 

 ful use of an electric eraser (see 4852) than by any other method. Hard abrasive 

 erasers should never be used, even for the removal of ink work. Colored erasers 

 should always be tested before use to determine whether the color rubs off, and if so, 

 they must not be used on the smooth sheet. 



The sheet in general may be cleaned by crumbling a small piece of art gum over it 

 and gently rubbing the crumbs across the surface with a piece of clean white paper 

 placed flat under the hand. Bread crumbs may be used for the same purpose. 



73. PREPARATION OF THE SMOOTH SHEET 



The completed smooth sheet is a valuable original document. It is preserved 

 indefinitely in the archives at the Washington Office. The amount of care taken to 

 protect the sheet during its construction wDl be directly reflected in its future longevity. 



731. Protection of Smooth Sheet 



Prior to and during the construction and plotting of the smooth sheet, the paper 

 should be kept in as dry a place as possible, especially if the climate is at all humid. 

 All drafting work is done much easier on dry paper. 



It is inevitable that the sheet will become slightly soiled while being worked on, 

 but there is no reason why it should be soiled excessively if a reasonable amount of 

 care is taken to keep all parts of the sheet covered, except the small area on which work 

 is actually being done. 



Smooth-sheet paper has a specially prepared surface and every care should be taken 

 to avoid damage to this surface. Lines should never be scratched on the paper, except 

 short arcs necessary in constructing a projection. This damages the surface and ink 

 runs in the scratches. It is equally unportant to avoid the indentations made by using 

 too hard a pencil or by pressing too heavily when drawing lines, particularly the con- 

 necting lines between positions (see 724). Smooth sheets have been received in the 

 Washington Office with the surface cut so badly by sharp pencils that in a short time 

 the paper cracked at these places. Wlien this occurs, deterioration of the sheet soon 

 follows. 



Temporary construction marks and temporary notes should be kept at a minimum, 

 and these, particularly the notes, should be made with as soft a pencil as practicable 

 so that they may be erased mthout damage to the paper. 



7311, Rolling the Smooth Sheet 



The mounted paper used for smooth sheets is of the best possible grade and if it 

 receives careful treatment during the making of the smooth sheet and subsequently, 

 it should suffer comparatively little distortion. If practicable, the smooth sheet should 

 be kept flat during the entire period of its construction. Rolling during this period is 



