when did they stop putting lead in glass
Lead glass 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%.[13] 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 (Pb3O4), white lead (2PbCO3·Pb(OH)2), 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.[13] The method used on a particular vessel may be deduced by analysing the interaction layer between the glaze and the ceramic body microscopically.
Architectural glass This method for manufacturing flat glass panels was very expensive and could not be used to make large panes. It was replaced in the 19th century by the cylinder, sheet, and rolled plate processes, but it is still used in traditional construction and restoration.