Methods of Staining Glass Windows
Two early methods of staining glass windows.
Now that the reader may be presumed to have a perfectly clear idea of the process of the early glazier, and to realise the distinctly mosaic character of old glass, it is time mention should be made of two important intermediate methods of glass staining which presently began to affect the character of stained glass windows.
Allusion has been made in Early History of Windows & Glass to the Roman practice of making glass in strata of two colours, which they carved cameo-fashion in imitation of onyx and the like ; at least, one tour de force of this kind is familiar to every one in the famous Portland vase, in which the outer layer of white glass is in great part ground away, leaving the design in cameo upon dark blue. The mediaeval glass-blower seems from the first to have been acquainted with this method of coating a sheet of glass with glass of a different colour. As the Roman coated his dull blue with opaque white glass, so he coated translucent white with rich pot-metal colour. It was not a very difficult operation. He had only to dip his lump of molten white into a pot of coloured glass, and, according to the quantity of coloured material adhering to it, so his bubble of glass (and consequently the sheet into which it was opened out) was spread with a thinner or thicker skin of colour. The Gothic craftsman took advantage of this facility, in so far as he had any occasion for its use. The occasion arose owing to the density of the red glass he employed, which was such that, if he had made it of the thickness of the rest of his glass, it would have been practically opaque. To have made it very much thinner would have been to make it more fragile; and in any case, it was easier to make a good job of the glazing when the glass was all pretty much of a thickness. A layer of red upon white offered a simple and practical way out of the difficulty.
What is called "ruby" glass, therefore, is not red all through, but only throughout one half or a third of its thickness. The colour is only, so to speak, the jam upon the bread; but the red and the white glass are amalgamated at such a temperature as to be all but indivisible, to all intents and purposes as thoroughly one as ordinary pot-metal glass.
For a long while glass painters used this ruby glass and a blue glass made in the same way precisely as though it had been self-coloured. But in shaping a piece of ruby glass, especially with their inadequate appliances, they would be bound sometimes to chip off at the edges little flakes of red, revealing as many little flaws of white. This would be sure to suggest, sooner or later, the deliberate grinding away of the ruby stratum in places where a spot of white was needed smaller than could conveniently be leaded in. As to the precise date at which some ingenious artist may first have used this device, it may be left to archaeology to speculate. It must have been a very laborious process; and the early mediaeval ideal of design was not one that offered any great temptation to resort to it during the thirteenth or even the fourteenth century. It was not, in fact, until the painting of windows was carried to a point at which there was some difficulty in so scheming the lines of the lead that they should not in any way mar its delicacy, that the practice of "flashing" glass, as it is termed, became common. That is why no mention of it has been made till now. It will be seen that it is a perfectly practical and workmanlike process, rendering possible effects not otherwise to be got in glass, but lending itself rather to minuteness of execution and elaboration of detail than to splendour of colour or breadth of effect.
The second intermediate method of staining glass began earlier to affect the design and execution of windows; and the character of fourteenth century glass is distinctly modified by it; and, curiously enough, whilst flashing applied to red and blue glass, this applies to yellow.
It was discovered about the beginning of the fourteenth century that white glass painted with a solution of silver would take in the kiln a pure transparent stain of yellow, varying, according to its strength and the heat of the furnace, from palest lemon to deepest orange. Observe that this yellow stain is neither an enamel nor a pot-metal colour, but literally a stain, the only stain used upon glass.
In pot-metal the stain (if it may be so called) is in the glass, this is upon it. But it is absolutely indelible; it can only be removed with the surface of the glass itself; time has no more effect upon it than if the glass were coated with yellow pot-metal. This silver stain was not only of a singularly pure and delicate colour, compared to which pot-metal yellows were hot and harsh, but it had all the variety of a wash of water-colour, shading off by imperceptible degrees from dark to light, and that so easily that the difficulty would have been in getting a perfectly flat tint.
Moreover, it could be as readily traced in lines or little touches of colour as it could be floated on in broad surfaces. By its aid it was as easy to render the white pearls on a bishop's golden mitre as to give the golden hair of a white-faced angel, or to relieve a white figure against a yellow ground and all without the use of intervening lead.
It is not surprising that such a discovery had a very important effect upon the development of the glass painter's practice. By means of it were produced extraordinarily beautiful effects, as of gold and silver, peculiarly characteristic of later Gothic work. The crockets and finials of white canopies would be touched with it as with gold, the hair of angels and the crowns of kings; or the nimbus itself would be stained, the head now being habitually painted on one piece of white glass with the nimbus. The crown and the pearl-edged head-band of the Queen of Sheba, from Fairford, are stained upon the white glass out of which the head is cut. In the figure of S. Gregory above the triple crown is stained yellow, and so is the nimbus of the bull, whose wings also are shaded in stain varying from light to dark.
Of the elaborate diapering of white drapery, with patterns in rich stain, more and more resorted to as the fifteenth century advanced, a specimen is here given, in which the design is figured in white upon a yellow ground, outlined with a delicately traced line of brown. Stain was seldom used on white without such outline.
In the end white and stain predominated. Early glass was likened to jewellery ; now the jewels seem to be set in gold and silver. There was a loss in dignity and grandeur, but there was a gain in gaiety and brightness. How far stain encouraged the more abundant use of white glass which prevailed in the fifteenth century it might be rash to say; at any rate, it fitted in to perfection with the tendency of the times, which was ever more and more in the direction of light, until the later Gothic windows became, in many instances, not so much coloured windows as windows of white and stain enclosing panels or pictures in colour. Even in these pictures very often not more than about one-third of the glass was in rich colour. And not only was more white glass used, but the white itself was purer and more silvery, lighter, and at the same time thinner, giving occasion and excuse for that more delicate painting which perhaps was one great reason for the change in its quality. At all events, the more transparent character of the material necessitated more painting than was desirable in the case of the hornier texture of the older make. Hence the prevalence of diaper already referred to.
This is Methods of Staining Glass Windows.
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