Technically, the term crystal is not applied to glass, as glass, by definition, lacks a crystalline structure. The use of the term lead crystal remains popular for historical and commercial reasons, and originally stems from the Venetian use of the word cristallo to describe the rock crystal imitated by Murano glassmakers. This naming convention has been maintained to the present day to describe decorative hollow-ware.
Lead oxide additives first appear in Mesopotamia, the birthplace of the glass industry. A red sealing-wax cake found in the Burnt Palace at Nimrud, from the early C6 BC, contains 10% PbO. These low values suggest that lead oxide may not have been consciously added, and was certainly not used as the primary fluxing agent in ancient glasses. Lead glass also occurs in Han-period China (206 BC – 220 AD). Here it was used in cast to imitate jade, both for ritual objects such as big and small figures, as well as jewellery and a limited range of vessels. Since glass occurs at such a late date in China, it is thought that the technology was brought along the Silk Road by glassworkers from the Middle East. and in 1676, having apparently overcome the crizzling problem, was granted the use of a raven’s head seal as a guaranty of quality. In 1681, the year of his death, the patent expired and operations quickly developed amongst several firms, where by 1696 twenty-seven of the eighty-eight glasshouses in England were producing flint glass containing 30–35% PbO, especially at London and Bristol. 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. Lin et al. have statistical evidence linking gout to lead poisoning.
Items made of lead glass may leach lead into the food and beverages contained. In a study performed at North Carolina State University, the amount of lead migration was measured for Port wine stored in lead crystal decanters. After two days, lead levels were 89 µg/L (micrograms per liter). After four months, lead levels were between 2,000 and 5,000 µg/L. White wine doubled its lead content within an hour of storage and tripled it within four hours. Some brandy stored in lead crystal for over five years had lead levels around 20,000 µg/L. To put this into perspective, the U.S. Environmental Protection Agency's lead standard for drinking water is 15 µg/L = 15 parts per billion. Citrus juices and other acidic drinks leach lead from crystal as effectively as alcoholic beverages. When lead-glass beverage containers are used in the ordinary usual way they do not pose a health risk. Under conditions of repeated use of the decanter, the lead leaching steeply decreases with increasing use. This finding is "consistent with ceramic chemistry theory, which predicts that leaching of Pb from crystal is self-limiting exponentially as a function of increasing distance from the crystal-liquid interface." Lead leaching still occurs, but the quantity that leaches into a glass of wine or other beverage let stand for a few hours is much smaller than the quantity of lead consumed daily in ordinary diet. An ordinary diet contains about 70 µg of lead per day.
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