Lead-Glass-Filled Ruby

Lead glass–filled ruby has its fractures filled with high-lead glass, and its appearance can resemble natural or other filled ruby, so unaided inspection cannot readily tell whether filling was applied. Recognition relies on laboratory testing: under magnification, gas bubbles, flow traces, and a blue flash effect appear within filled fractures, X-ray imaging can show heavy elements along fractures, energy-dispersive or mass spectrometry (EDXRF, LA-ICP-MS) can confirm elements such as lead, and infrared spectroscopy can also indicate glass filling. Whether filling is present and the filler composition must be judged by an accredited laboratory, and this entry provides no self-test threshold.

Scope: Safety boundary: appearance is insufficient to decide filling status; determination requires testing by an accredited laboratory, and this entry gives no self-test threshold.

Origin determination concerns natural material, whereas lead-glass-filled ruby is a gem product treated by lead-glass filling, to which natural origin determination does not apply. For such material the treated or synthetic status must itself first be established by an accredited laboratory using instrumental testing; until then an origin discussion is meaningless. Origin cannot be inferred from appearance or name; and even where some natural material is involved, any origin claim must be issued by an accredited laboratory for a specific specimen. No self-test criteria are given here.

Scope: Origin cannot be inferred from appearance or name; natural origin determination does not apply to this material and its treated/synthetic status must first be established by a laboratory; any conclusion must be issued by an accredited laboratory for a specific specimen; no self-test criteria are given here.

Since the early 1980s glass has been used to fill badly fractured rubies, improving both clarity and durability; cavity filling was already being reported by 1984. The first filler material was silica glass, whose refractive index of roughly 1.5 made it easy to detect.

Scope: GIA's account of the history of glass-filling treatment of rubies; it concerns no individual specimen.

In early 2004 a new glass filler with high lead content and a refractive index of about 1.70 appeared, giving better clarity enhancement; since then lead glass has become the most popular filler for rubies.

Scope: The source cites the 2004 GAAJ lab alert; other glass types (e.g. bismuth, cobalt) have also been used.

Stones that are heavily fractured are treated by lead-glass filling, whereas those with fewer fractures are given heat treatment (optionally with borax-like additives) — so filling is the approach chosen for badly cracked material.

Scope: Concerns processing practice for Mozambique (Montepuez) ruby; practice elsewhere may differ.

Lead glass is artificially produced glass with a distinct high content of lead oxide; filling means occupying part or all of a fracture/cavity with a substance to make it less visible.

Scope: CIBJO's general definitions of lead glass (5.50) and filling (5.28/5.34); no specific chemical proportions are given.

A lead-glass-filled ruby is a treated gem product, not a natural formation; the treatment must be disclosed under the standard.

Scope: Based on CIBJO's definitions of treatment and treated gemstones; whether a given stone is filled must be confirmed by a gem laboratory.

GIA's ruby care guide says today's fracture-filled rubies are filled mainly with high-lead glass and need more care than untreated or heated ruby: many chemicals can damage the glass, even mild acids such as lemon juice, and such stones should be cleaned only with a damp cloth.

Scope: General consumer guidance for fracture-filled, cavity-filled and dyed ruby; it is stricter than the outcome of GIA's 2006 laboratory tests on steam and ultrasonic cleaning (see this entry's finding on those durability tests).

In GIA's 2006 durability tests the lead-glass filler began to sweat out of fractures at 700 °C, placing its melting point at 600–700 °C in those samples. Careful steam cleaning, ultrasonic cleaning, setting and prong retipping caused no damage to the few stones tested, but the authors warn that too much torch heat could still harm the filler and advise unmounting before repairs. The filler reacted readily with a jeweller's pickling solution. Caustic soda and aqua regia etched it quickly, and household oven cleaner, ammonia, bleach and even concentrated lemon juice etched it at the surface.

Scope: Results apply to the samples tested in 2006 (retipping on only three stones, done by highly skilled jewellers); the authors note that a different glass composition could change the melting point. This is not a guarantee that steam or ultrasonic cleaning is safe for any given stone.

The laboratory harmonisation committee's information sheet on glass-filled corundum warns that the glass filler may be unstable to high temperatures and to chemical agents, that special care is needed when repairing jewellery set with such stones, and that unmounting them for repair is recommended.

Scope: Standard report wording agreed by the member laboratories for glass-filled corundum in general, not only lead glass.

Trade disclosure manuals give consistent care advice. AGTA rates the stability of glass-filled ruby (code F) as fair to poor and says to avoid heat, ultrasonic cleaning and common household chemicals; for lead-glass-filled ruby composites (code CMP) it also lists abrasives and sudden shocks. CIBJO rates lead-glass-filled ruby as unstable and says fillers can scratch more easily than the host and be vulnerable to heat or some acids, so keep them away from chemicals, heat and abrasives.

Scope: Trade-standard care codes; they are stricter than GIA's 2006 test results on cleaning (see this entry's finding on those durability tests) and reflect the cautious trade position.