I do periodically write about this issue as I am not convinced that – even though the practice has been around for a while – it is yet common knowledge. In short, glass filling is the practice of fracture-filling rubies with lead glass to improve their appearance. I’m going to lay it on the line, folks: this is bad. It takes poor quality, fractured material and turns it into pretty looking transparent red. It looks good but it is complete junk. Worse than that, it is no longer a ruby.
What is the treatment?
Fracture-filling is not new; emeralds have been fracture-filled with oil for years, and it is a completely accepted treatment. The idea being that you find a filler with the same or similar refractive index as the stone and the appearance of fractures are minimised. With emeralds this is fine, as oil is used, which can be removed if necessary and the stones re-oiled; in addition, the original material is usually reasonable. With rubies, the practice of lead glass filling takes rough that is opaque or near opaque – material that would otherwise be unsaleable – and permanently filling it with lead glass. Poor quality corundum is soaked in acid to remove mineral inclusions leaving a weakened and brittle stone; a stone so weak in fact that you could crumble it to powder with your hands. These skeletons are then infused with lead glass, which makes the stone stronger and prettier. The results are actually extraordinary: opaque corundum can be turned into stones with high transparency. So what’s the problem?
The Problems with Glass Filling
There are three main problems: firstly it is an extremely unstable treatment, secondly – and rather crucially – once a ruby has been glass filled it is no longer a ruby and thirdly, it is frequently not disclosed. Let’s take these one by one:
- The GIA reports describe glass filled rubies like this: ‘ A manufactured product consisting of lead glass and ruby…unstable to high temperatures and to chemical agents.’ This says it all. The treatment is extremely unstable. Heat during jewelry making or repair will ruin it. Pickle to remove fire-scale will ruin it. Even the wearer can ruin it – most household cleaners will ruin it. Lemon juice will ruin it.
- The stones are not rubies. They are ruby and glass composites and in many cases will be more glass than ruby.
- The treatment is not disclosed. Sometimes this is blatant fraud; sellers will blatantly charge ruby price for something that is effectively worthless. I have suppliers who say they are finding glass filled rough in with the decent stuff. But most of the time it’s happening because people simply don’t know. They go to a show and buy a ruby and think, ‘oh I got a great deal’ and then sell the stone in jewellery as ruby. Sometimes even the big stores are selling these items undisclosed and, since I’m sure these stores don’t want to wreck their reputations, it must be that they simply don’t know what they are selling. From my own experience, I myself have found at gem fairs that when I’ve asked, ‘is this glass filled?’ that sellers have readily told me. But I have not been convinced that they would have done so, had I not asked.
This is really important, because the retailer is completely liable, whether the mistake is deliberate or accidental, they can be sued for not disclosing this treatment.
How is it detected?
Well, the good news is that unlike other nefarious treatments, this one is really easy to spot under magnification. A microscope or even a loupe will show up low relief fractures, gas bubbles (as is really common with glass), voids, and a yellow and blue flash effect. Failing this, one of the easiest ways – in my experience from attending gem fairs – is simply looking at the price: if it looks too good to be true, it probably is. That is, if you are looking at near-transparent ruby for a few dollars a carat, it’s probably glass-filled. This is fine if you’re buying at this stage – the danger comes if someone thinks they’ve got a great deal, and sell the stone on as ruby.
What’s the take-home message?
I’m not pulling punches with this because it really is complete rubbish. If you buy it and sell it on you are liable. There are also reports that it is being seen in sapphire as well as ruby, although the ruby composites are completely ubiquitous. Always, always ask, if you are buying a ruby. First question: ‘is it glass filled?’ In my experience, you will be told. Carry a loupe and learn how to use it. It’s not even always deliberate fraud; sometimes the sellers themselves don’t know what they’ve got on their hands. And remember, forewarned is forearmed.