30 THE ART OF PROJECTING, 



a piece of hard soap, enough will adhere to it to make 

 the glass semi-opaque. Now draw the design with a 

 fine-pointed stick. It will clear the soap from the glass, 

 and so permit the light to shine through the marks. 

 This has the advantage of permitting the same glass to 

 be used like a slate, for with a drop of water upon the 

 finger the old design can be rubbed out, leaving the 

 glass coated for another picture. The same thing can 

 be done with a surface of beeswax, but the glass would 

 need heating in order to re-spread the wax. 



2. For more permanent pictures, a very good way is 

 to flow the glass with photographers' transparent var- 

 nish, and then scratch the design upon the varnish, not 

 cutting through to the glass. The light is so much 

 scattered from this scratched surface, that it appears as 

 a dark line, and answers a very good purpose. The 

 prepared plate can be laid over the design wanted if it 

 is to be a copy, and is of proper size ; the transparency 

 allows the picture to be plainly seen, and all its mark- 

 ings can easily be followed. The varnish is quite hard 

 when dry, and with a little care in handling these pic- 

 tures, they need not become scratched. They can be 

 entirely protected from that danger by covering them 

 with another clean glass of the same size, and binding 

 their edges with paper, as common lantern-pictures are 

 bound. Photographers have also another kind of var- 

 nish called ground-glass varnish, which, when spread 

 upon glass, gives it an appearance similar to ground 

 glass. This surface permits drawing with a pencil or 

 with ink upon it, and then a coat of the transparent 

 varnish will render the first coat transparent, leaving 

 the lines in ink or pencil ; or the design may be drawn 

 through the first coat of varnish, in which case, the light 

 will shine through the lines and appear white upon the 

 screen. 



