The Making of a Window
The basics of how to make a window.
Since it is proposed to approach the subject of stained glass in the first place from the workmanlike and artistic, rather than the historical or antiquarian, point of view, it may be as well to begin by explaining precisely what a stained glass window is.
It is usual to confound "stained" with "painted" glass. Literally speaking, these are two quite distinct things. Stained glass is glass which is coloured, as the phrase goes, "in the pot"; that is to say, there is mixed with the molten white glass a metallic oxide which stains it green, yellow, blue, purple, and so on, as the case may be; for which reason this self-tinted glass is called "pot-metal". This is a term which will recur again and again. Once for all, "pot-metal" is glass in which the colour is in the glass and not painted upon it.
It goes without explanation that, each separate sheet of pot-metal glass being all of one colour, a vari-coloured window can only be produced in it. by breaking up the sheets and putting them together in the form of a mosaic : in fact, that is how the earliest windows were executed, and they go by the name of mosaic glass. The glass is, however, not broken up into tesserae, but shaped according to the forms of the design. In short, those portions of it which are white have to be cut out of a sheet of white glass, those which are blue out of a sheet of blue glass, those which are yellow out of a sheet of yellow, and so on ; and it is these pieces of variously tinted glass, bound together by strips of lead, just as the tesserae of a pavement or wall picture are held in place by cement, which constitute a stained glass window. The artist is as yet not concerned in painting, but in glazing, that is to say, putting together little bits of glass, just as an inlayer does, or as a mosaic worker puts together pieces of wood, or marble, or burnt clay, or even opaque glass.
There is illustrated a piece of Old Burmese incrusted decoration, a mosaic of white and coloured glass bound together by strips of metal, which, were it but clear instead of silvered at the back, would be precisely the same thing as an early mosaic window, even to the completion of the face by means of paint, of which more presently. In painted glass, on the other hand, the colour is not in the glass but upon it, more or less firmly attached to it by the action of the fire. A metallic colour which has some affinity with glass, or which is ground up with finely powdered glass, is used as a pigment, precisely as ceramic colours are used in pottery painting. The painted glass is then put into a kiln and heated to the temperature at which it is on the point of melting, whilst the colour actually does melt into it. By this means it is possible to paint a coloured picture upon a single sheet of white glass, as has been proved at Sevres.
Strictly speaking, then, stained and painted glass are the very opposite one to the other. But in practice the two processes of glazing and painting were never kept apart. The very earliest glass was no doubt pure mosaic. It was only in our own day that the achievement (scientific rather than artistic) of a painted window of any size, independent of glazier's work, was possible. Painting was at first always subsidiary to glazier's work; after that, for a time, glazier and painter worked hand in hand upon equal terms; eventually the painter took precedence, and the glazier became ever more and more subservient to him. But from the twelfth to the seventeenth century there is little of what we call, rather loosely, sometimes "stained" and sometimes "painted" glass, in which there is not both staining and painting, that is to say, stained glass is used, and there is painting upon it The difference is that in the earlier work the painting is only used to help out the stained glass, and in the later the stained glass is introduced to help the painting.
That amounts, it may be thought, to much the same thing; and there does come a point where staining and painting fulfil each such an important part in the window that it is difficult to say which is the predominating partner in the concern. For the most part, however, there is no manner of doubt as to which practice was uppermost in the designer's mind, as to the idea with which he set out, painting or glazing; and it makes all the difference in the work, the difference, for example, between a window of the thirteenth century and one of the sixteenth, a difference about which a child could scarcely make a mistake, once it had been pointed out to him.
This is The Making of a Window.
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