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.