In colour, however, which after all is the most important thing in a window, this glass is splendid, and for the quality of the material and the way in which it has resisted the attacks of time it is superior to much glass of a later date.
[1] Pliny's word "nitrum" does not mean what we call nitre, which is potassium nitrate, but natron, or natural carbonate of soda, of which deposits are found in the Nile Delta. It is this that is meant in the passage in Jeremiah: "Though thou wash thee with nitre, and take thee much sope...."
[2] These panes are, I believe, of cast glass; but I have seen Roman window glass found at Silchester that was obviously "blown" glass and of very good quality.
[3] By some writers it has been claimed that the whole idea of stained-glass work was derived from cloisonné enamel; but from the fact that the glazing of windows in glass and metal had been known long before, I think the course of events I have suggested above to have been more probable.
[4] There is some at Augsburg and at Tegernsee in Bavaria which may perhaps be a little earlier, but it is not certain.
Stained glass from its birth to the Renaissance has been divided by Winston into three main periods, each having broad characteristics peculiar to itself, and which he named after the corresponding architectural styles, Early English, Decorated, and Perpendicular. As, however, these terms only apply to English work, and as the architectural styles do not altogether correspond in date with those of the glass, I prefer to speak simply of the First, Second, and Third Period.
The First lasts from the earliest examples almost to the end of the thirteenth century, and might be subdivided again into twelfth and thirteenth century work, between which there is a distinct difference.
The Second covers nearly the whole of the fourteenth century.
The Third lasts down to the end of the fifteenth century, by which time the influence of the classic Renaissance began to be felt in glasswork, but lingers on in belated examples well into the sixteenth.
Between each of these periods there is a very short transitional period lasting hardly a decade, and occupying the closing years of each century.
It must not be thought, however, that at any time design in stained glass stood still. Its history is rather one of periodic impulses, due no doubt to the work of individual genius, followed in each case by a long and gradual decline, towards the end of which artists began to grow restless and feel about for new modes of expression, and so prepare the way for the next impulse of genius.