ON MICROSCOPICAL DRAWING AND PAINTING. 177 



should be of the finest quality, the paper, hard, thin, 

 smooth, and unglazed ; delicate pencil drawings 

 may be made on Bristol board, but such or any 

 glazed or hot-pressed surfaces are totally unfitted 

 to take colour. Fine drawing paper is preferable, 

 when blocks are used each surface must be ex- 

 amined for imperfections with a hand lens ; a 

 delicate painting may be ruined, at a critical point, 

 by an imbedded hair, an abrasion, or minute speck ; 

 in the manufacture of these blocks, it has been 

 found that in cutting up and folding the paper the 

 true surface is not in every piece placed uppermost. 

 For important work it is safer to select sheets 

 strained in the usual way, in a small-sized folding 

 drawing frame. Paper improves by age. If of 

 undoubted antiquity, it fetches high prices. It is 

 impossible to render satisfactorily, on a white sur- 

 face opaque preparations showing minute injected 

 anastomosing veins, arteries, or glands, the dark 

 interstices separating them, cannot be drawn, or 

 picked out, without sacrificing the regularity or 

 destroying the uniform diameter of the vessels 

 but such subjects may be effectively painted on a 

 dull black paper, which may be previously pasted 

 on a drawing block under pressure, using opaque 

 or body colour, vermillion, yellow ochre, Antwerp 

 blue, and carmine, combined with and regulated 

 for substance and tint, with zinc white and gum 

 water. Payne's grey, with zinc white, produces 

 the peculiar shadowy hyaline tone so often seen as 

 a substratum in such preparations where semi- 

 transparent spongy tissues are involved fine effects 

 of receding distances in following the depths of 

 structures, may be produced by its use. Numerous 

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