Lo qual diretro a sè piombo nasconde’;
and in the twenty-third book of the Inferno (25-26) Virgil says to the poet, ‘S’io fossi d’impiombato vetro—I should not more quickly receive your image than now my mind receives your thoughts.’ This double reference would seem to point to a recent discovery that had attracted Dante’s attention.
In the thirteenth and fourteenth centuries it would appear that although the German mirror-makers had to import the clear crystalline ‘metal’ from Venice, the Venetians attempted in vain to make mirrors on the German system. The difficulty, perhaps, was to prepare flat and even sheets of glass of any size, and this difficulty the Germans may have surmounted by means of the cylinder process described by Theophilus.
The Nuremberg mirrors, however, so famous at a later time, were of a different type. They were of spherical outline, cut directly from the paraison of the glass-blower; into this paraison a mixture of ‘piombo, stagno, marchesita d’argento e tartaro’ had been introduced before the vesicle was quite cool—so at least a contemporary Italian writer asserts. Such mirrors were set in painted wooden frames with broad margins. An example of one of these may perhaps be seen in Jan van Eyck’s famous interior in the National Gallery.
If now we turn to England, the record is even more meagre. Mr. Hartshorne, who has industriously brought together every reference he could find to glass[[99]] in this country during the Middle Ages, is fain to confess that he cannot point to a single example of what is undoubtedly English glass made between the Norman Conquest and the time of our Tudor kings. References to its use in contemporary writers are much rarer than in France. The cuppa vitrea, which in 1244 Henry III. sent to his goldsmith, Edward of Westminster, directing him to remove the glass foot, to replace it by one of silver, and to mount the whole in silver-gilt, was probably of Oriental origin; nor can we even claim for certain as English the two humbler vessels belonging at a later time to his son, Edward I.[[100]]
As to the three ‘verrers’ of Colchester who paid taxes about the year 1300, the distinction between vitrier and verrier does not seem to have been as sharp then as it is now; they may well have been makers of glass windows. It is more significant to find in Henry III.’s day a Laurence Vitrearius holding land at Chiddingfold in Surrey, still in the time of Elizabeth a centre for the manufacture of the native glass made of fern-ash and sand. Again, William le Verir of the same place is mentioned in a deed of 1301. But perhaps the strongest case is that of John Glasewrythe of Staffordshire, who in 1380 had a grant of house and land at Shuerwode, Kirdford,[[101]] and there made ‘brodeglass and vessel’—that is to say, window-glass and hollow ware (Nesbitt, South Kensington Catalogue, and Hartshorne, p. 132, etc.).
I reserve what I have to say of the mediæval glass of Italy—of the early Altarists and Muranists—until I have described the enamelled Saracenic glass which in some measure influenced it.
But before turning again to the East, I must not omit to mention certain applications of glass that found favour in Western Europe during the later Middle Ages; indeed, apart from the coloured windows, such objects constitute the only genre of glass that can distinctly be classed as Gothic. I group together here various devices by means of which a design or pattern was applied to the back of a small sheet of glass—in gold for the most part, but other colours were sometimes used. The plaque thus decorated was either fixed into a piece of furniture, or simply backed with some impervious material. In this somewhat indefinite group is included, on the one hand, what is in fact a kind of thin mosaic; on the other, something that passed into the variety of painted glass known in later times as verre églomisé. What distinguishes all this class of decoration is that neither the colour nor the backing is fixed by any furnace process—it is scarcely to be regarded as an art du feu, and thus lies somewhat outside our subject.
Of the so-called Cosmati mosaics, where the little triangular pieces of glass are inlaid in marble or wood, we have a good example in the thirteenth-century shrine of the Confessor in Westminster Abbey. At the same period a more elaborate means of decoration was obtained by painting the backs of little plaques of glass with gold and colours, and fixing them on the panels of pulpits, on the frames of the painted reredos, or even on secular furniture. I have seen examples of church furniture thus decorated at Aachen and in the Norman churches of Southern Italy—a pulpit at Bitonto in Apulia is a remarkable example. But we need not go far to find a still finer specimen of such work: the Gothic framework of the retabulum that formerly was placed in front of the high altar in Westminster Abbey[[102]] is decorated with bosses of glass paste cut or cast en cabochon, with casts of antique gems, and, above all, with little plaques of blue and purple glass backed with silver foil. On the upper surface of these glass plaques a design in gold, consisting of small medallions with animals and twining branches, stands out in low relief. The pattern, says Viollet-Le Duc (Dictionnaire du Mobilier français, i. 338), was first painted on the glass with a mixture of red ochre, wax and turpentine, and over this, before it was dry, gold leaf was laid, the gold adhering only to the soft ground. The effect of this external decoration is heightened by the shadow which it throws upon the silver foil beneath.
In other examples, the pattern is painted in various colours under the glass, and a leaf of gold, pasted beneath the more or less transparent pigments, shows through here and there. In all these instances the crude colour of the gold is lowered in places by coatings of varnish.