[Sidenote: The two parts of the process.]
The process thus consists of two parts. The cutting and putting together of the glass is called _glazing_, and it is this that gives the window colour; while the enamel work is spoken of as _painting_, and gives detail, richness, and texture.
I shall presently show that the glazing and painting are really two separate crafts, having separate origins and development, and that stained glass as we know it, or as it should be called in strict accuracy "stained-and-painted" glass, is the product of their union.
There is another method, far inferior in the beauty of its results, by which pictures can be produced in glass, which is to paint on white glass with transparent coloured enamels. As, however, this method was not used till the seventeenth century, and is now once more almost wholly abandoned, it does not concern us here.
The softness of lead which makes it the only practicable metal for joining pieces of glass of complicated shapes, has the disadvantage that a stained-glass window when leaded up has a considerable degree of flexibility, and, if held by the edges alone, would be quite unable to resist the pressure of the wind, which on a big window is enormous,--think of the power even of a fresh breeze on a boat's sail.
It would not even be able to support its own weight for long, and so it follows that it must be held up by a system of short metal bars fixed firmly into the stone-work. Naturally the design of the window must be so arranged that these bars either do not interfere with it or form an integral part of it. In early windows, especially those of the twelfth and thirteenth centuries and even to some extent in those of the fourteenth, the bars are sufficiently important to form the governing factor in the design.
It must not be thought that stained glass loses in beauty by the presence of these black lines of lead and iron. On the contrary it gains enormously. Large pieces of unrelieved colour in windows are thin in effect and trying to the eye, which needs the continual contrast of the solid black of the lead all over the window to enable it to appreciate the colour and brilliance of the glass. The painting when rightly used is directed to the same end, for it may be said that the smaller and more divided the spaces of clear glass, the more brilliant and jewel-like is the effect.