Lead-glass filled rubies have been creeping slowly into the jewelry market, and are now the most abundant ruby material used. Even from the wholesale level they are sometimes undisclosed, making their way to retailers as loose stones or finished jewelry; which should be a widespread concern for jewelers and buyers alike.
What exactly are lead-glass filled rubies and why is this a big deal?
Lead-glass filled rubies, also known as composite rubies, typically start out as very included, dark ruby rough that would otherwise be unworkable. The rough or polished stone is then treated multiple times by being exposed to high heat while submerged in a lead-glass solution, which is a permanent fusion process of the ruby material with the lead-glass filler. The result is a gemstone far better in appearance of the rough it came from, but at a cost of the stability and durability of the stone. Due to a significant portion of the gem being composed of glass, these stones are sensitive to high temperatures, many cleaning solutions, and exposure to direct sunlight. A simple jewelry repair or maintenance process such as resizing or polishing can be detrimental to a lead-glass filled ruby.
If the end result from this enhancement has a completely different chemical makeup, is considerably more vulnerable to damage, and contains more filler than corundum – how can you still call it a natural ruby? It is more accurate to describe these gems as composite, reconstituted, or even man-made rubies. The lead-glass serves as the “glue” that holds together the skeleton of the actual ruby.
Lead-glass rubies should not be confused with “treated” rubies.
As this type of treatment is relatively new to the industry, many market these rubies as being “treated” when it should be directly listed as lead-glass filled. Other traditional and widely accepted enhancement procedures (mainly heat-treatment and fillers) do not affect day-to-day handling of the stone.
Why use lead-glass?
The reason lead-glass is used is because it can be formulated so that its refractive index (R.I.) is the same as ruby’s. The refractive index of a stone relates to the way light moves through it. The greater the difference between the R.I. of each substance, the more easily you can see the different components; the closer the R.I., the more difficult it is to see them. If the R.I. is the same for both substances, you cannot distinguish where one ends and the other begins.
What is the difference between lead-glass in composite rubies and the silica glass fillers in “treated” rubies?
- Silica glass is more durable than lead-glass
- Rubies that are treated with silica glass use much less of it than composite rubies use lead-glass
- The lead-glass cannot be separated from a composite ruby without causing irreparable damage; silica glass filler can be safely removed from a treated ruby to return to its original state, and after it can be refilled
- Because lead-glass cannot be safely removed, composite rubies cannot be accurately graded for clarity or color. It is possible to grade for color and clarity with silica glass rubies (after removal of the filler)
- Carat weight – the representative carat weight of composite rubies is misleading because it accounts for the combined weight of the lead-glass and ruby material. What makes it even worse is that lead-glass is 50% heavier! Since traditionally glass-treated rubies use very little silica glass, it has very little, if any, impact on the carat weight.
- Value – all composite rubies are very inexpensive, at the wholesale level they only go for a few dollars per carat; treated/natural rubies start at 20 times the value and up, depending on quality
- Detectability – silica glass filled rubies is easier to spot with the naked eye, as there is an R.I. difference between materials. Most lead-glass filled rubies are difficult to identify by the naked eye because the R.I. of lead-glass and ruby is the same, but close up under a jeweler’s microscope the tell-tale air bubbles and flashes of blue are a dead giveaway.
The bottom line for a buyer would be to find a retailer who has someone who can identify any treatments made to a stone, a Graduate Gemologist or similar who has undergone formal gemological training. At the very least, do not buy any rubies without an official gemological certification stating its treatments (if any). You pay for what you get. There are no discounts for quality rubies, they are very rare and in high demand. Use common sense, get a stone with a lab certificate or have it certified, and buy from a knowledgeable jeweler.