SCIOPTICON MANUAL. 141 



sharp instrument so as to show upon the screen in 

 smooth white lines upon a dark ground. The varnish 

 must be thinned with turpentine, to allow of tracing by 

 superposition. 



This process, obtained by purchase, is given for the 

 benefit of teachers, who will find it admirably suited for 

 maps, diagrams, and any so-called blackboard exercises. 



ORDINARY TRANSFERS UPON GLASS. Coat, by prefer- 

 ence, quarter-plate B. P. C. glass on the hollow side 

 with transfer varnish, and let it partially dry. Take any 

 cut of proper size, place it upon water right side up un- 

 til it becomes wet to saturation, adjust it to the varnished 

 surface face down, rub up the paper in rolls until it is 

 mostly removed, and then lay it aside until the varnish 

 becomes hard. Much of the remaining paper can now 

 be removed without damaging the picture, by carefully 

 wetting and rubbing. 



Grecian varnish will render the picture transpar- 

 ent; but unfortunately innumerable pimples make their 

 appearance, which show badly on the screen, caused by 

 the loosened fibres of the remaining paper film. Several 

 coats of varnish will finally leave a smooth surface, but 

 so thick a coating will before long crack and eventually 

 peel off. 



This process is here referred to because it is so often 

 inquired about, rather than because it is thought to be 

 of much value. 



DIAPHANIE. A picture on thin, smooth paper, treated 

 as above, but without rubbing off any of the back 

 surface or even roughing it up, will make a tolerable 

 lantern slide, with one coat of the varnish. It will ap- 

 pear dark on the screen like a silver print that is very 

 much "fogged." If the picture is pasted to a frame 



