136 SCIOPTICON MANUAL. 



breathing on and thoroughly rubbing it with tissue- 

 paper is sufficient for the cleaning. Of course the fin- 

 gers must not touch the surface of the glass after it is 

 cleaned. 



The next step is to prepare the surface of the glass 

 for the drawing. If the glass (as is usual with this kind) 

 is slightly curved, the concave side should invariably be 

 the surface to receive the preparation. This preparation 

 is as follows : " The plate to be dusted and gently warm- 

 ed; then flow the surface with No. 1 varnish, and drain 

 into the bottle from the corner of the glass. When this 

 is dry, flow with No. 2 in the same manner, and after- 

 wards dry with gentle heat. Of course until the var- 

 nish is dry the corner from which the varnish was 

 drained should be kept down. Should dust find its way 

 into the varnish, it can be filtered." Having prepared 

 the surface, it should not be soiled by handling (always 

 take the glass by the edge between the fingers). A 

 sketch can now be made on the surface with a good 

 hard black-lead pencil, either as an original drawing, 

 with the glass on the easel, or by placing the glass on 

 an engraving or other picture, and tracing the outline. 



When this sketch or outline is finished, strong and 

 black lines and marks can be made with the " liquid 

 India-ink " in a fine pen, gently used so as not to make 

 the lines too coarse and heavy. With the pen, too, lines 

 can be ruled or letters or figures added. After the 

 drawing is finished and dry, any little corrections or 

 scratches can be made with the pointed eraser. 



The easel should be so placed that the light falling on 

 the white tablet will be reflected to the eye of the artist 

 through the inclined glass on which the picture rests, 

 and consequently the picture will be illuminated by 

 transmitted light. 



The easel may stand on a table placed against a win- 



