Crystal glass
5-8 usd/kgCrystal glass is known for its incredible clarity and brilliance. Also called lead alkali glass, the inclusion of lead oxide (PbO) dramatically improves optical properties compared to regular glass, as well as increasing density, workability and machinability. The lead acts as a flux, reducing the softening point of the glass to around 600 degC, and so makes it relatively easier to blow, mould and manipulate. It also reduces the surface hardness, which allows for greater freedom with cutting, grinding and polishing processes. The optical qualities of crystal are often emphasised with facets, cuts and engraving that reflect and refract light – typified by Swarovski crystal.
The use of lead is problematic, because it is toxic and a heavy metal – particulates from crystal glass manufacture may have a lead content of 20-60%. Prolonged exposure to the element is potentially very harmful, especially for babies and children. As part of the EU REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) regulation, the lead content of jewellery and similar items is restricted.
In the case of finished crystal glass, the lead is locked into the structure and so does not present the same health concerns in use. For example, crystal glass is exempt from REACH regulation. Small amounts are thought to transmit from the glass to stored contents through diffusion ionic exchange, and so it is not recommended for long term storage. For short term storage, such as during a meal, the rate of leaching is so minute that it is not thought to be a risk. Acid polishing is a technique used to enhance surface brilliance, whilst also reducing the concentration of lead at the surface, further reducing the risk of contamination.