鉛玻璃
鉛玻璃或水晶玻璃是玻璃的一種，與一般碳酸鉀玻璃最大的不同為其中的鈣被鉛取代[1]。鉛玻璃通常含有18至40%氧化鉛 (PbO)，不過現代的鉛水晶 (Lead Crystal，又因其氧化矽起源而被稱為燧石玻璃) 至少含有24%氧化鉛[2]。鉛玻璃常因其裝飾性而被收藏。
Originally discovered by Englishman George Ravenscroft in 1674, the technique of adding lead oxide (in quantities of between 10 and 30%) improved the appearance of the glass and made it easier to melt using sea-coal as a furnace fuel. This technique also increased "working period" making the glass easier to manipulate.
The term lead crystal is, by technicality, not an accurate term to describe lead glass, as glass, an amorphous solid, lacks a crystalline structure. The use of the term lead crystal remains popular for historical and commercial reasons. It is retained from the Venetian 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.[3]
Lead crystal glassware was formerly used to store and serve drinks, but due to the potential health risks of lead, this is rare nowadays. One alternative material is crystal glass, in which barium oxide, zinc oxide, or potassium oxide are employed instead of lead oxide. Lead-free crystal has a similar refractive index to lead crystal, but it is lighter and it has less dispersive power.[4]
In the European Union, labeling of "crystal" products is regulated by Council Directive 69/493/EEC, which defines four categories, depending on the chemical composition and properties of the material. Only glass products containing at least 24% of lead oxide may be referred to as "lead crystal". Products with less lead oxide, or glass products with other metal oxides used in place of lead oxide, must be labeled "crystallin" or "crystal glass".[5]
備註
- ^ Newton, Roy G.; Sandra Davison. Conservation of Glass. Butterworth – Heinemann Series in Conservation and Museology. London: Butterworths. 1989. ISBN 0-408-10623-9.
- ^ Hurst-Vose, Ruth. Glass. Collins Archaeology. London: Collins. 1980. ISBN 0-00-211379-1.
- ^ Tait, Hugh (编). Five Thousand Years of Glass. University of Pennsylvania Press (orig. British Museum Press). 2004. ISBN 978-0-8122-1888-6.
- ^ About Lead-free Crystal.
- ^ Council Directive 69/493/EEC of 15 December 1969 on the approximation of the laws of the Member States relating to crystal glass.