One of the chief glories of the later Middle Ages in Western Europe is undoubtedly to be found in the stained glass windows of the churches. Theophilus early in the twelfth century had already made himself master of this art, which he regarded as essentially a French one. The preparation of these vitraux involved a knowledge of the process either of spinning the molten paraison or of opening out the cylinder of glass, both comparatively late developments of the art of glass-blowing. In the staining of the glass we know from extant specimens what splendid results were obtained.
The composition of the window-glass of the thirteenth century is in some ways remarkable. It contained as much as from 8 to 10 per cent. of alumina, which we must regard as replacing in a measure the silica, for this constituent falls to as low as 56 per cent., and we can hardly otherwise account for the high percentage of the other bases—14 per cent. of lime, 17 per cent. of potash, and often 3 or 4 per cent. of iron. The result was a tough, somewhat horny glass, hard to work in consequence of the short duration of the viscous stage during the cooling. This was one reason for the smallness of the gatherings, and the modest dimensions of the resultant discs. On the other hand, such glass resists the action of the atmosphere better than any made nowadays, and the large amount of potash present probably promoted the brilliancy of the colours. From the earliest times the blue colouring was given by cobalt, and this was never of a richer and purer tint than in the twelfth century; already in the thirteenth copper was added to correct a tendency to purple. The famous ruby red, which became rarer after the thirteenth century until in the seventeenth the secret was entirely lost, was produced by the partial reduction of a small quantity of suboxide of copper, but in this case the colour is only developed on reheating the glass. The more purplish tint given by a somewhat similar treatment with gold was not known to the mediæval glass-maker.[[95]] Manganese was of course the source of the purple—the colour was used for flesh-tints in the twelfth century! The green was made by a mixture of the æs ustum or copper scale with a native oxide of iron, the latter often known as ferretto—of this the best came from Spain. Finally, the yellow was given either by the sesqui-oxide of iron kept well oxidised by the presence of bin-oxide of manganese, or (where the surroundings favoured a reducing action) by a mixture of sulphur and some sooty material which probably yielded an alkaline sulphide. But in the older glass the yellow colour was never very brilliant; at a later time a fine yellow was obtained by a cementation process from silver, which was applied as a chloride or a sulphide to the surface of the glass.
If I trespass beyond my limits to give this rapid summary of what is known of the colours of mediæval window-glass, it is because much of it will be found applicable to the contemporary Oriental enamelled ware and to the later Venetian glass.
In view of the high technical skill thus shown in the colouring and working of the material, nothing is more remarkable than the almost total absence from our collections of any glass, using that word in the narrower sense, that we can classify as Gothic. We know, indeed, that during these centuries much glass was made in France, Germany, and Italy. But for one reason or another the material was not in favour for objects that had any claim to be regarded as works of art. And yet during all this time the few rare specimens of sculptured glass brought from Constantinople, or of enamelled glass from Egypt and Damascus, were highly prized, and it might well be thought that the skill and knowledge to rival these examples were not wanting in the West. Such was not the case, however; the monasteries had ceased to be centres of practical art industry,[[96]] and the glass-makers had retired from the towns to the depths of the forests, where under the patronage of the local seigneur they built their glass-houses, moving on from one spot to another as the fuel became scarce.
On the condition of delivering yearly to their feudal lord a specified number of vessels, these glass masters appear to have been freed from further imposts, and indeed they soon began to claim special privileges. In France some of these grants or contracts have been preserved in local archives, and in them we have a source of information lacking in other Western countries. Perhaps the most significant of these patents is that granted in 1338 to a certain Guionet. The Dauphin of the Viennois conceded to this maître de verrerie the right of taking wood when it suited him from parts of the forest of Chamborant, on condition that the said Guionet should furnish him yearly, for the use of the prince’s household, with the following pieces of glass:—240 beakers with feet, known as hanaps; 144 amphoræ, 432 urinalia, 144 large basins, 72 plates, 72 plates without borders, 144 pots, 144 water vessels, 60 gottefles, 12 salt-cellars, 240 lamps, 72 chandeliers, 12 large cups, 12 small barils, 6 large vessels for transporting wine, and one nef. This was certainly an ample yearly supply even for a princely household. The practical, not to say homely, nature of most of the objects requisitioned is obvious. The gottefle, we should add, has been thought to correspond with the later German gutraf; it was in that case a vase with a long twisted neck, sometimes double, like a Persian sprinkler; it was perhaps used for oil.[[97]] The nef, no doubt, was an imitation in glass of the well-known centre-pieces of silver in the form of a ship. The little baril is a form handed down from Roman times. In Provence, as early as the year 1316, we find mention in the inventory of the property of the Countess Mahaut D’Artois of ‘Grant planté de pots de voirre et de voirres d’Aubigny et de Provence et d’autres païs et de diverses couleurs et bocaux et bariz’ (Hartshorne, p. 88).
We see by this how little ground there is for giving the credit of the introduction of the manufacture of glass into France to King René. We shall find, however, later on, that this great patron of the arts was one of the earliest to take an interest in the Venetian glass of the early renaissance, and to bring the Italian workmen into France.
The word verre, or in the earlier form voirre or vouarre, was used vaguely in France even in mediæval times for any cup from which wine was drunk. This usage alone might be brought forward as a proof of the general prevalence of glass vessels at an early time. Modern French writers on glass cannot always escape the awkward expression ‘un verre de verre.’ In England, where the use of the word glass in this sense probably came in somewhat later, we find more than once in inventories of the fourteenth century the quaint combination, ‘un verre de glass.’ In France, however, the more frequent expression was ‘un verre de fougère,’ literally ‘a glass of bracken,’ and we have here a double metonymy. This association of bracken and glass may be frequently noticed in the old French writers.
Long after the introduction of the cristallo from Italy, there were many in France who preferred to drink from the old greenish glass; like the Germans of to-day, they declared that the wine tasted better. Even Boileau, late in the seventeenth century, talks of a man holding ‘un verre de vin qui rit dans la fougère.’
We see then what an important place bracken, feucheria ad faciendum vitrum, played in the old glass-works of France. Now glass made from fern-ashes must of necessity be of a very inferior quality, more so probably than that made from the beechwood ashes used from of old in Germany. The passage to the new methods would here be much more revolutionary than in the case of the latter country. This consideration may help to explain the fact that while the manufacture of potash glass survived and adapted itself to the new methods in Germany, it became in time quite extinct in France.
The chronicles and romances of the thirteenth, fourteenth, and fifteenth centuries have been carefully searched by French scholars to find references to glass. Some ambiguity arises from the vague use of the word verre, to which I have already referred. But when Joinville tells us how the Comte d’Eu, in a moment of expansion, ‘dressait sa bible le long de nostre table et nous brissoit nos pots et nos vouerres,’ we can probably accept the latter vessels as verres de verre.