Of Painting The Glasses
You first draw on a paper, the size of the glass, the subject you mean
to paint; fasten this at each end of the glass with paste, or any
other cement, to prevent it from slipping. Then with some very black
paint mixed with varnish, draw with a fine camels'-hair pencil, very
lightly, the outlines sketched on the paper, which, of course, are
reflected through the glass. Some persons affirm that those outlines
can be more
readily traced with japan writing ink, and a common pen
with a fine nib; but this, even if it succeeds in making a delicate
black outline, is sure to be effaced by damp or wet.
It would improve the natural resemblance, if the outlines were drawn
with a strong tint of each of the natural colours of the object; but
in this respect you may please your own fancy. When the outlines are
dry, colour and shade your figures; but observe, to temper your
colours with strong white varnish. A pleasing effect will be produced,
if you leave strong lights in some parts of the drapery, &c., without
any colours. The best colours for this purpose are transparent ones;
opaque or mineral colours will not do. The following are in most
repute.
For Pink and crimson Lake or carmine.
Blue Prussian blue.
Green Calcined verdigris, or distilled ditto.
Yellow Gamboge.