Glass or Ruby?

How can I tell if a stone set in a ring is a ruby or just a piece of glass? I have a jeweler’s loop, but I don’t know what to look for.

Most of the garnets I’ve seen are much darker.

Most real rubies are flawed. Most things that fall into the category of glass, synthetic, etc. are rather perfect inside. If you’re using a 10x loupe, you can almost always see the flaws in a real ruby.

Garnets can range from pink to red/brown. I have a pink one.

Inclusions of corundum (Ruby & Sapphire)

And here I thought this was going to be about Cinderella versus Dorothy.

I am so gay.

Corundum is much harder than glass, too, isn’t it? I mean, you probably don’t want to try cutting your stone to test it, but that’s always an option :D.

When I wanted to know if a ring I fould was valuable, I took it to a jeweler.

Just my whacky way of doing things, I guess.

Or even a pawn shop. They have hardness testers and are experts at evaluating actual market price. Make sure you tell them that you are not interested in selling it or they will low ball you on an estimate.

Jewelers have a thing called the Mohs Hardness Scale, in which gems are rated by whether they will scratch other gems. It’s kinda like playing Rock/Paper/Scissors.

Ruby will scratch glass, but glass will not scratch ruby, and so you can tell. But–do not try this at home, because you can wreck your ruby if you scratch it improperly. Go ask a jeweler to do it for you.

I believe that jewellers also use a spectroscope to analyse the light emitted by a gemstone. Spectroscopes look like largish tubes of lipstick.
It shows the jeweller a kind of rainbowlike pattern, similar to the ones you get through a prism. The pattern thrown by light reflected by red glass is different from that of a ruby.

PICUNURSE…Okay…now I’m confused. I thought garnets and rubies were completely different stones; one is semi-precious and one is precious. Are you saying they’re just different shades of the same thing?

Carbuncle and ruby are words that mean red jewel. Some famous red rubies are actually red spinels. Nowadays, when we say ruby we mean red corundum. Pink Corundum is pink sapphire. Red Garnets are carbuncles but not all garnets are carbuncles. The minerals we call garnets do have a wide color range, wider than PICUNURSE indicated; some are even green.

Thanks, Lee!

A ruby will brighten perceptibly in sunlight as compared to incandescant light, but so will a spinel; except a spinel will not brighten as much.

Some other things to look for: What is the cut of the stone like? Colored glass usually has a simple style of cutting in which many of the facets you would see on a more expensive stone are missing. For instance, if it’s a round stone vaguely in the style of a brilliant cut diamond, there will usually be just a single circle of facets around the top half of the stone. A genuine mined or synthetic ruby will usually have a more precisely and elaborately done cutting job. If the stone has a good cut and bright red color, but seems free of inclusions, then you probably have a synthetic ruby.

Please correct me if I’m wrong, but I read somewhere that rubies and spinels can be somewhat hard to distinguish from one another by eye. It is only when more modern methods of analysis were applied that those stones were found to be spinels.

And a question: Is there some official distinction between “precious” and “semiprecious” stones? I know diamonds, rubies, sapphires and emeralds are “precious” and amethysts and peridot are “semi-precious,” but what about things like spinel? And do the terms precious and semi-precious have any real meaning in the lapidary(?) world, or are they just marketing terms?

The words are fairly subjective without a clear demarcation. Traditionally, diamonds, rubies, emeralds, and pearls have been classified as “precious” and everything else is “semi-precious”. But it’s not nearly so clear-cut. A mediocre sapphire will be worth less than a top-quality amethyst or garnet; I have a 1-carat sapphire that cost me $9 at a gem show. It has wonderful optical characteristics, but is off color which is why it was so cheap. Further complicating things is that other types of stones, such as opals, have a wide array of various colors and types which vary tremendously in value, but are all genuine. For example, the green garnets mentioned above are usually very valuable; in some ways they surpass the qualities of emeralds and may be more expensive than some of them.

One is denser than the other, and density has been used as a way to differentiate substances for a very long time. They are also of different hardnesses, while still both being harder than glass or quartz. Red spinels and rubies are colored by the same element and do appear very much a like with similar fire, etc. I don’t think that it was a matter of it being impossible to distinguish them, as much as there was no motivation to. It may well be that those making the jewelry knew there were at least two types of ruby; it would be difficult to not notice that some are denser and harder than others. The famous red spinels are famous because they are beautiful and amazingly large, true gems in every sense.

I don’t see how this could be possible, given that sunlight is incandescant light. The only difference between two incandescant light sources is temperature, and even that’s pretty close between light bulbs and the Sun (except for long-life lightbulbs). Unless you’re just referring to the fact that the Sun is brighter than a light bulb, but in that sense, everything will brighten in sunlight.

Unless you meant to compare sunlight to fluorescent lights? The spectrum of even high-quality fluorescents is very different from that of any incandescant (including the Sun), and it’s quite possible that this might show differently in a glass stone or a real gem.

It’s the UV. Most (but not all) genuine rubies will fluoresce red when exposed to UV–it’s the trace chromium content, which is also why rubies can made to lase. However, if the ruby contains as little as 1% iron, it will not fluoresce very much, if at all.

No, I do have the idea of rubies brightening in sunlight from a highly reputable source, the Simon & Schuster Guide to Gems and Precious Stones.

Isn’t the UV component missing from a lightbulb, or significantly reduced, as compared to sunlight?