After the Restoration the issue of patents began again. Everything points at this time to a renewal of interest in Venetian glass. When, however, in 1663 the Duke of Buckingham obtained his licence, his claim was based upon the improvements he had made in the looking-glass plates and in the plates for the glass-coaches. As in France, sheets of large size and good material were now in demand for both purposes. It was somewhat later, it would seem, that he turned his attention to making hollow ware in the Venetian fashion. Although nitre, a salt of potash,[[245]] played an important part in the glass made by the duke, there is no proof that any use was made of red lead or of litharge. Evelyn, who in 1673 visited the duke’s ‘Italian glass-house at Greenwich where glasse was blown of finer metal than that of Murano at Venice,’ says nothing about such substances being employed.
But in spite of this progress in the home industry, the importation of chests of glass from Venice was at its height in the reign of Charles II. This we see from the correspondence of a London glass merchant, one John Greene (1667-1672), with a Venetian firm, which has fortunately been preserved.[[246]] Along with these letters were found the ‘office copies’ of the patterns which Greene sent out to Venice as a guide to the glass-blowers. Here we have mention of ‘clouded calsedonia glasses’ for beer, claret, and sack, ‘creuits with or without feet, brandj tumblers,’ and ‘glasse floure potts.’ Not the least interesting item is the ‘Rhenish wine glasse,’ which is illustrated by a typical roemer with prunts on the stem, almost our only evidence of the use of these goblets in England. Greene advises his Venetian correspondent that the looking-glasses and the coach-glasses are to be packed at the bottom of the cases to escape if possible the search of the custom-house officials. What especially strikes one in examining the patterns of the drinking-glasses, which form the bulk of the orders (Hartshorne, Plates 30-32), is the fact that the stem or shank, so important a part of the eighteenth-century glass, is not yet developed; the conical bowl is separated from the foot by a simple or fluted bulb, or sometimes by two such bulbs or knops.
But this Venetian trade had now seen its best days; there are some hints of a falling off in Greene’s last two letters (1671-1672). On the other hand, during all this period the enterprising glass firms of the Netherlands kept up a close intercourse with England. As early as 1662 a patent for making various kinds of glass was obtained by one John Colenet, whom Mr. Hartshorne has very plausibly claimed as a member of the great glass-making family of Ghent and Namur, the De Colnets, so often mentioned in the letters of M. Schuermans. A few years later the tables were turned, for now the De Colnet firm was fain to engage an Englishman to produce ‘verre à l’Angleterre.’ In 1680 the great rival firm of Liége, the De Bonhommes, according to a document quoted by M. Schuermans (Letter vii.), was already making ‘flint-glass à l’Anglaise.’
Now this statement brings me face to face with what is the great crux in the history of English glass—the question, namely, when and where lead-glass was first applied to the manufacture of hollow ware.
But first I must say a word of a little book published in 1662. This is the already-mentioned translation by Christopher Merret of the Arte Vetraria of Antonio Neri (see p. 7). Merret, who was a man well abreast of the science of his day and an early, if not an original, member of the newly founded Royal Society, has supplemented Neri’s series of recipes with certain ‘Observations’ of his own. Here may be found some curious information concerning the materials used in the manufacture of the cristallo, for it is with this glass that the author is chiefly concerned. Merret does not appear to have had much acquaintance with the glass made in England in his day. For the practical details of the furnace and for the processes of glass-blowing he takes us back to Agricola. Both Neri and his translator are indeed for the most part occupied with the nature and preparation of the materials, and with the various methods by which glass may be coloured.[[247]] Neri, like all the old writers, knew of the merits of lead-glass in the preparation of pastes for the manufacture of artificial gems; in his sixty-first section he tells us: ‘Glass of lead, known to few in this art, as to colour is the finest and noblest glass at this day made in the furnace. For in this glass the colours imitate the Oriental gems, which cannot be done in crystal. But unless diligence be used all sorts of pots will be broken, and the metal will run into the furnace.’ Upon this passage Merret observes: ‘Glass of Lead! ’Tis a thing unpractised in our furnaces, and the reason is because of the exceeding brittleness thereof.’ Lead, he continues, is indeed the principal ingredient in the glaze of the potter, ‘and could this glass be made as tough as Crystalline, ’twould far surpass it in the glory and beauty of its colours.’ Thus we see, with Merret as with Neri, the great merit of lead-glass is the capacity possessed by it of bringing out the colours of metallic oxides. They still regard the material from the mediæval point of view. The bad working qualities of this glass of which Merret complains may very probably have been due to the fact that, starting from the basis of their cristallo, the glass-workers continued to use the soda-holding barilla instead of employing a potash salt.
The Venetians in the preparation of their cristallo laid great stress on the hard white pebbles, the cogoli, from the bed of the Po or of the Ticino; these they regarded as an essential constituent of a good glass. We in England, during the reign of Charles II., succeeded in replacing these pebbles by our native flints; and this English flint-glass,[[248]] properly so-called, early acquired a good reputation on the Continent. The ingenious Mr. John Houghton, writing in 1683 (Letters for the Improvement of Husbandry and Trade), after speaking of our dependence upon the Venetians some years since, goes on to say: ‘Now by the fashion of using glasses in coaches and other good means we easily enough serve our neighbours.’ In 1682 he tells us there were exported from England two thousand five hundred and seventy-two drinking-glasses, besides some looking-glasses and ‘window chests.’ This confirms what I have said of the date when English flint-glass became well known in the Low Countries. Now it is generally taken for granted that by this time the term flint-glass had come to mean lead-glass. Certainly soon after the beginning of the next century lead-glass was already recognised as essentially a substance of English origin; but, as I have said, there is unfortunately not a word of evidence, documentary or otherwise, to show when or where this glass was first made, nor is it possible, I think, to point to any example of this lead-glass to which an earlier date than the first or second decade of the eighteenth century can be attributed. Indeed everything points to the English flint-glass of the last quarter of the seventeenth century being a form of the Venetian cristallo.
In any case it is essential to bear in mind that both in chemical composition and in physical properties no two things could be more unlike than the cristallo on which the early flint-glass, properly so called, was founded, and the lead-glass which afterwards usurped the name.[[249]] The one is a typical soda-lime, the other an equally definite potash-lead glass, and the materials had to be sought for from entirely different sources.
The above-mentioned Mr. John Houghton, who every week, in the commercial paper edited by him, published an article on some technical or scientific subject, in the spring of 1696 devoted a series of these ‘leaders’ to the subject of glass. After some general reflections on the substance, when we are told, among other things, that ‘Vitrification is the last mutation of bodies of which Nature is capable and from which there is no going back,’ in his issue of May 2 he takes up the main subject. ‘According to my information,’ he tells us, ‘we are of late greatly improved in the art of Glass-making. For I remember the time when the Duke of Buckingham first encouraged glass-plates, and Mr. Ravenscroft first made Flint-glass.[[250]] Since then we have mended our Window-glass and outdo all abroad. And what e’er may be said against Stock-Jobbery, yet it has been the Means to raise great Summs of Money to improve this Art.’ Again, on May 16 we are given a carefully classified list of ninety glass-houses existing in England. Of these, twenty-four were in London, nine at Bristol, seventeen at Stourbridge, and eleven at Newcastle. These glass-houses he divides into those for looking-glass plates, for bottles and for ‘Flint, Green, and Ordinary.’ Now the rational inference from all this seems to me to be that Houghton, who was in a position to know, knew nothing about lead-glass. The flint-glass houses are classed together with the ‘green’ and ‘ordinary,’ and flint-glass for him was glass made from flints.
So, as we have seen, Haudicquer de Blancourt, writing in France a few years earlier, knew nothing of lead-glass other than that used for objects of verroterie. It is at least evident that if our own glass-makers had mastered the art before the end of the century, the secret was well kept.[[251]]
But before proceeding further, it may be well to form some definite idea of the composition of lead-glass and of the physical properties that led to its replacing in great measure the soda-lime glass of Venetian type. In the first place, as I have said, it is essential that the alkali in this glass (in the manufacture of hollow ware, at least) should be potash, and it was, perhaps, the fact that the lead was at first used along with soda that so long delayed the production of a ‘metal’ suitable for the manufacture of blown-glass. Again, the potash in the case of lead-glass must be something quite different from the impure material employed for the old green glass; this crude alkali contained, among other bases, a large percentage of lime. Saltpetre appears to have been used in the first place, and then a more carefully lixiviated form of vegetable ashes known as pearl-ash. The amount of lead oxide may vary from 28 to 40 per cent., and the specific gravity of the resultant glass from 2·8 to 3·6.