Monday, February 09, 2009
Lead crystal (also called crystal) is lead glass that has been hand- or machine-cut with facets. Lead oxide added to the molten glass gives lead crystal a much higher index of refraction than normal glass, and consequently much greater "sparkle" by increasing specular reflection and the range of angles of total internal reflection. Ordinary glass has a refractive index of n=1.5, whereas the addition of lead produces a range up to 1.7. This heightened RI also raises the correlating index of dispersion, which measures the degree to which a medium separates light into its component spectra, as in a prism. The presence of lead also makes the glass softer and easier to cut. Crystal can consist of up to 35% lead, at which point it has the most sparkle. The higher lead content also makes it much more difficult to form crystal during manufacturing.
Makers of lead crystal objects include Baccarat and J.G.Durand (Arc International) in France, Royal Leerdam Crystal of the Netherlands, Steuben Glass in the United States, Waterford Crystal in Ireland, Mikasa in Japan, Liuligongfang in Taiwan, Swarovski in Austria, Preciosa in Czech Republic and Rogaška Crystal in Slovenia.
It has been proposed that the historic association of gout with the upper classes in Europe and America was, in part, caused by their extensive use of lead crystal decanters to store fortified wines and whisky. Lin, et al. have statistical evidence linking gout to lead poisoning.
Significant amounts of lead can migrate from lead crystal containers into beverages stored in them. Lead crystal typically contains 24–35 percent lead oxide. 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, EPA's lead standard for drinking water is 15 µg/L = 15ppb. Citrus juices and infant formula leach lead from crystal just as effectively as alcoholic beverages. Several companies do make lead crystal baby bottles and it is suspected they may present a health danger to infants.
Pictured above: Small lead crystal vintage bowl, made in Italy and available at our CHShops.com Mall Store at: http://pennysantiquesandwedgwoodpantry.chshops.com/index.php?main_page=product_info&cPath=20_35&products_id=396