<P> From the 18th century, English lead glass became popular throughout Europe, and was ideally suited to the new taste for wheel - cut glass decoration perfected on the Continent owing to its relatively soft properties . In Holland, local engraving masters such as David Wolff and Frans Greenwood stippled imported English glassware, a style that remained popular through the eighteenth century . Such was its popularity in Holland that the first Continental production of lead - crystal glass began there, probably as the result of imported English workers . Imitating lead - crystal à la façon d'Angleterre presented technical difficulties, as the best results were obtained with covered pots in a coal - fired furnace, a particularly English process requiring specialised cone - furnaces . Towards the end of the eighteenth century, lead - crystal glass was being produced in France, Hungary, Germany, and Norway . By 1800, Irish lead crystal had overtaken lime - potash glasses on the Continent, and traditional glassmaking centres in Bohemia began to focus on colored glasses rather than compete directly against it . </P> <P> The development of lead glass continued through the twentieth century, when in 1932 scientists at the Corning Glassworks, New York State, developed a new lead glass of high optical clarity . This became the focus of Steuben Glass Works, a division of Corning, which produced decorative vases, bowls, and glasses in Art Deco style . Lead - crystal continues to be used in industrial and decorative applications . </P> <P> The fluxing and refractive properties valued for lead glass also make it attractive as a pottery or ceramic glaze . Lead glazes first appear in first century BC to first century AD Roman wares, and occur nearly simultaneously in China . They were very high in lead, 45--60% PbO, with a very low alkali content, less than 2% . From the Roman period, they remained popular through the Byzantine and Islamic periods in the Near East, on pottery vessels and tiles throughout medieval Europe, and up to the present day . In China, similar glazes were used from the twelfth century for colored enamels on stoneware, and on porcelain from the fourteenth century . These could be applied in three different ways . Lead could be added directly to a ceramic body in the form of a lead compound in suspension, either from galena (PbS), red lead (Pb O), white lead (2PbCO Pb (OH)), or lead oxide (PbO). The second method involves mixing the lead compound with silica, which is then placed in suspension and applied directly . The third method involves fritting the lead compound with silica, powdering the mixture, and suspending and applying it . The method used on a particular vessel may be deduced by analysing the interaction layer between the glaze and the ceramic body microscopically . </P> <P> Tin - opacified glazes appear in Iraq in the eighth century AD . Originally containing 1--2% PbO; by the eleventh century high - lead glazes had developed, typically containing 20--40% PbO and 5--12% alkali . These were used throughout Europe and the Near East, especially in Iznik ware, and continue to be used today . Glazes with even - higher lead content occur in Spanish and Italian maiolica, with up to 55% PbO and as low as 3% alkali . Adding lead to the melt allows the formation of tin oxide more readily than in an alkali glaze: tin oxide precipitates into crystals in the glaze as it cools, creating its opacity . </P>

When did they stop putting lead in glass
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