Lead crystal is a type of glass in which lead replaces the calcium content of a typical potash glass. It contains typically 18-40% lead(II) oxide (PbO), while modern lead crystal, historically also known as flint glass due to the original silica source, contains a minimum of 24% PbO. The addition of lead oxide raises the glasss refractive index, which means that lead glass has a more reflective appearance than traditional glass. Leaded glass also stays malleable for longer periods of time when heated, making it easier for artisans to work with.
It is important to note that the term "lead crystal" is technically not an accurate term to describe lead glass because glass lacks a crystalline structure and is instead an amorphous solid. The use of the term "lead crystal" remains popular for historical and commercial reasons, and sometimes simply "crystal" because "lead" seems toxic to consumers.
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 "crystalline" or "crystal glass".
It is not recommended to drink out of lead crystal pieces because lead can leach into the liquid and pose a health risk. However, lead crystal is often found in the form of vintage decanters, glasses, and goblets. The safest way to know if something is lead crystal is by having it lab tested. However, if youd like to test items in your home, in an antique shop, or at a flea market, you can try the following techniques to identify the differences between crystal and glass:
- Tap it with a metal utensil. Lead crystal will produce a musical ring, while glass will produce a duller sound.
- Hold it up to the light. Lead crystal will refract light in a rainbow pattern, while glass will not.
- Look for a hallmark. Many manufacturers will mark their lead crystal pieces with a hallmark or logo.
