Fig. 31.
It requires a good deal of patience and practice to lay matt successfully over unfired outline. It is a question of the amount and quality of the gum, the condition of your brush, even the dryness or dampness of the air. You must try what degree of gum suits you best, both in the outline and in the matt which you are to pass over it. Try it a good many times on a slab of plain glass or on the plate of your easel first, before you try on your painting. Of course it's a much easier thing to matt successfully over a small piece than over a large. A head as big as the palm of your hand is not a very severe test of your powers; but in one as large as the whole of your hand, say a head seven inches from crown to chin, the problem is increased quite immeasurably in difficulty. The real test is being able to produce in glass a real
facsimile of a head by Botticelli or Holbein, and when you can do that satisfactorily you can do anything in glass-painting.
Do not aim to get too much in the first painting, at any rate not till you have had long practice. Be content if you get enough modelling on a head to turn the outline into a more sensitive and artistic drawing than it could be if planted down, raw and hard, upon the bare, cold glass. After all it is a common practice to fire the outline separately, and anything beyond this that you get upon the glass for first fire is so much to the good.
But besides the quality of the gum you will find sometimes differences in the quality or condition of the pigment. It may be insufficiently ground; in which case the matt, in passing over, will rasp away every vestige of the outline, so delicate a matter it is.
You can tell when colour is not ground sufficiently by the way it acts when laid as a vertical wash. Lay a wash, moist enough to "run," on a bit of your easel-slab; it will run down, making a sort of seaweed-looking pattern—clear lanes of light on the glass with a black
grain at the lower end. Those are the bits of unground material: under a 100-diameter microscope they look like chunks of ironstone or road metal, or of rusty iron, and you'll soon understand why they have scratched away your tender outline.
You must grind such colour till it is smooth, and an old-fashioned granite muller is the thing, not a glass one.
Now, after all this, how am I to excuse the paradox that it is possible to have the colour ground too fine! All one can say is that you "find it so." It can be so fine that it seems to slip about in a thin, oily kind of way.
It's all as you find it; the differences of a craft are endless; there is no forecasting of everything, and you must buy your experience, like everybody else, and find what suits you, learning your skill and your materials side by side.