Lead-glass filling is a treatment that fills fissures and cavities in corundum, mostly ruby, with high-lead glass to hide them.
In more detail
It usually applies to low-quality stones. Colored flashes in the fissures can give it away. The glass is unstable to heat and to some chemicals; even lemon juice can change it. Clean these stones with a damp cloth only.
On a grading report
Indications of heating, glass-filled fissures (and cavities), extent minor (F1), moderate (F2) or significant (F3). Badly fractured rough held together by glass is a manufactured product.
Related terms
- Manufactured product: A manufactured product is a gem held together by glass or resin. It is made from badly fractured rough, or from many small pieces bound into one.
- Clarity enhancement: Clarity enhancement is filling surface-reaching fissures with a filler such as oil, resin, wax or glass, so they show less.
- Ruby: Ruby is the red variety of the mineral corundum. Chromium causes its red color.
- Stability: Stability is a gem's resistance to damage from heat, light and chemicals.
- Disclosure: Disclosure is telling the buyer, before the sale, that a gem is treated, laboratory-grown or an imitation.