Glass or Crystal; what is crystal exactly?
Glass to which lead oxide has been added may be called crystal. According to European regulations, crystal must contain more than 10% lead oxide. If it contains more than 30% lead, it is high lead crystal, such as eg Swarovski crystal (approximately 32% lead).
The higher the lead content, the higher the refractive index. Glass / crystal with a high refractive index shows more brilliance and has a richer color spectrum (think about a rainbow...).
The English glassmaker George Ravenscroft was the first to produce clear lead crystal glass on an industrial scale in 1676.
Designation Lead content
Crystal: from 1% lead content
Designation: Lead content
Glass : less than 4% lead content
(half) Crystal : more than 10% lead content
Lead crystal : at least 24% lead content
High Lead Crystal : more than 30% lead content
3 types of crystal used in antique chandeliers:
1. Rock crystal (pure quartz, from the mountains)
2. Lead crystal (lead oxide added to the glass)
3. Crystal glass (a collective name for all glass that is colourless)
Most chandeliers from the last century are papered with glass or semi-crystal. The chandelier's cones were poured into a mold and then grinded. This grinding could be done mechanically or manually.
To assess the quality of the glass / crystal, pay attention to:
- the quality of the mold.
- the quality of the grinding (including the evenness and sharpness of the lines).
- the quality of the glass used.