Let us say that you see an oil-painting—a portrait—at the end of the large room in some big Exhibition. You stand near it and say, "Yes, that is the King" (or the Commander-in-Chief), "a good likeness; however do they do those patent-leather boots?" But after you have been down one side of the room and turn round at the other end to yawn, you catch sight of it again; and still you say, "Yes, it's a good likeness," and "really those boots are very clever!" But if it had been your own painting on glass, and sitting at your easel you had at last said, "Yes,—now it's like the drawing—that's the expression," you could by no means safely count on being able to say the same at all distances. You may say it at ten feet off, at twenty,
and yet at thirty the shades may all gather together into black patches; the drawing of the eyelids and eyes may vanish in one general black blot, the half-tones on the cheeks may all go to nothing. These actual things, for instance, will be the result if the cheeks are stippled or scrubbed, and the shade round the eyes left as a film—ever so slight a film will do it. Seen near, you see the drawing through the film; but as you go away the light will come pouring stronger and stronger through the brush or stipple marks on the cheeks, until all films will cut out against it like black spots, altering the whole expression past recognition.
Try this on simple terms:—
Do a face on white glass in strong outline only: step back, and the face goes to nothing; strengthen the outline till the forms are quite monstrous—the outline of the nose as broad as the bridge of it—still, at a given distance, it goes to nothing; the expression varies every step back you take. But now, take a matting brush, with a film so thin that it is hardly more than dirty water; put it on the back of the glass (so as not to wash up your outline); badger it flat, so as just to dim the glass less than "ground
glass" is dimmed;—and you will find your outline look almost the same at each distance. It is the pure light that plays tricks, and it will play them through a pinhole.
And now, finally, let us say that you may do anything you can do in the painting of glass, so long as you do not lay the colour on too thick. The outline-touches should be flat upon the glass, and above all things should not be laid on so wet, or laid on so thick, that the pigment forms into a "drop" at the end of the touch; for this drop, and all pigment that is thick upon the glass like that, will "fry" when it is put into the kiln: that is to say, being so thick, and standing so far from the surface of the glass, it will fire separately from the glass itself and stand as a separate crust above it, and this will perish.
Plate [IX.] shows the appearance of the bubbles or blisters in a bit of work that has fried, as seen under a microscope of 20 diameters; and if you are inclined to disregard the danger of this defect as seen of its natural size, when it is a mere roughness on the glass, what do you think of it now? You can remove it at once by scraping it with a knife; and indeed, if through accident a touch here and there
does fry, it is your only plan to so remove it. All you can scrape off should be scraped off and repainted every time the glass comes from the kiln; and that brings us to the important question of firing.