2 1 6 DRA WINGS FOR PHO TO-ENGRA VING. {APPEND J X. 



board drawings and so cheap that there is no temptation to preserve them after their 

 usefulness is past, one may adopt the suggestion of Dr. Dunnington of the Uni- 

 versity of Virginia and make the diagrams on manilla paper with ordinary black- 

 board crayons, and then fix them so that they will not rub by hanging them where 

 the face cannot touch and putting the fixative on the back with a brush or a sponge. 

 The fixative may be readily prepared by mixing one liter (iooo cc.) of ordinary 

 painter's turpentine with ioo cc. of dammar varnish. If these are well shaken to- 

 gether the dammar will be dissolved in the turpentine, and then if the mixture is 

 put on the back of the diagram it will soak through the paper and upon drying, 

 will fix the crayon lines so that they will not rub. At the present day black black- 

 board crayons are manufactured and they are somewhat easier to shade with, and 

 very much cheaper for all black work than the Conde crayons. The Conde cray- 

 ons are better for lettering, however. 



It requires only about 12 hours for the fixative to dr} . Diagrams may be used 

 in less time, but they should not be rolled much sooner. If one wishes to have 

 rollers, and they are very convenient, they are easily made by using what the car- 

 penters call " half-round." If two of these are used, the paper being put between, 

 and then the sticks nailed together, very neat looking diagrams are produced. Of 

 course if it is desired, water colors may be used upon these diagrams either before 

 or after the crayon has been fixed. 



In making diagrams from figures in books, if one desires to enlarge a definite 

 number of times the drawing paper should be laid out in squares. If these are 

 made lightly in pencil they will not show in the finished diagram unless one scans 

 it closely. 



DRAWINGS FOR PHOTO-ENGRAVING. 



(WRITTEN BY MRS. GAGE). 



I 361. The inexpensive processes of reproducing drawings bring within the 

 reach of every writer upon scientific subjects the possibility of presenting to the 

 eye by diagrams and drawings the facts discussed in the text. Though artistic 

 ability is necessary for perfect representation of an object, neatness and care will 

 enable any one to make a simple illustrative drawing, from which an exact copy is 

 obtained and a plate prepared for printing. 



\ 362. A shaded drawing prepared by washes of India ink can be reproduced by 

 the " half-tone process," which is the same as that used in the case of photographs. 

 (See \ 351, Figs. 160-161). The process usually called photo engraving is that by 

 which all the line drawings in this book were reproduced, and is much less expen- 

 sive than the "half-tone" process. For photo-engraving, only pure black and 

 white can be used in the drawing, as shades of gray are not successfully repro- 

 duced. 



I 3°3- Outfit for Drawings. — A perfectly squared drawing board ; a T-square ; 

 thumb tacks ; a right-line pen ; a circle pen ; an assortment of smooth pointed 

 pens, including for fine work a lithographic pen ; very soft, hard, and medium 

 pencils; fine scissors; fine forceps; a 'sharp-pointed knife or scalpel; smooth, 

 white bristol board ; perfectly black ink. To test the ink draw extremely fine 

 lines and look at them with a magnifying glass. Most of the water-proof and 

 liquid India inks on the market answer well. 



\ 364. Size of Drawing. — It is first necessary to decide upon the scale at which 

 the drawings are to be made. It is always recommended that they be made large, 



