As a true ruby aficionado, I’ve been just waiting for July to roll around the calendar. As young gem dealers Laura and I spent months in Thailand early on in our careers. Among our missions there, learning about ruby was towards the top of the list. Over the years we’ve spent months (perhaps years) in Southeast Asia dealing in rubies and enjoying every exciting and even every frustrating minute of it.

Based on price per carat and price per stone, ruby is probably the king of all colored stones. On a price per stone basis there may be some good competition with emerald. This may well be due to the fact that emerald comes in bigger sizes than ruby.

For instance if you were to examine the crown jewels of England, Russia and France and then move on to the great museum collections of the world, you would find that the large emeralds in those collections are bigger than the large rubies. This would appear to be a mineralogical issue. Some minerals simply occur in larger crystals than others. In the case of fine ruby, the crystals just do not seem to get very big.

There are exceptions in non-gem ruby. In east Africa, years ago, there were giant crystals of ruby found which were imbedded in zoisite (Anyolite). In this case the zoisite happened to be a nice green color. Since the ruby was not gem quality and since the green of the zoisite was attractive, slices of this material were cut and polished, many up to 10 inches square. In other cases the material was used for carvings, beads, or cabochons. Some of these ruby crystals were up to as much as 3 inches across—some even more. While not gem quality, they were just as beautiful.

But the sad truth remains that rubies just do not occur in great quality in big sizes. Fine rubies of 5 carats easily bring 6 figure prices. Larger fine rubies trade in the 7 figure bracket. However, the dynamic nature of the gem business has played games with prices and availability of ruby.

For decades—even centuries—the Mogok valley of Burma (Myanmar) has been the source of the best rubies the world has known. What is it that makes the Burmese rubies so desirable? Their color.

To understand what it is that makes a color desirable we have to go back to some deceptively simple basics. The simple truth is that desirable colors in gems are based on what is attractive to the largest number of people. Specific colors in specific gems that are considered to be desirable colors have, by and large, been asked and answered in the market place over and over for centuries. In most cases it has only been after the free marketplace has answered the question of desirability that any codified or generally accepted answer to that question becomes generally accepted.

An example of this comes from diamond. Years and years of the diamond trade has found out that truly white diamonds dazzle and attract the eye better than their straw-yellow counterparts. It is simply what people like, over and over, that later becomes codified and in the case of diamonds “official.”

Rubies: color, color, and more color

So what is it through the years in the color of ruby that people like or dislike? Since one definition of ruby is “red corundum,” we have to get down to examining the color red. As with any color in gems a person will never realize how many colors of red there are until he decides to learn about ruby.

There are two predominant issues: depth of color and purity of color and the deviations away from that purity. As to the depth of color, the way to discuss this was brought up by C.R. “Cap” Beesley who, more than 30 years ago, devised a color grading system for many colored stones. While his color grading system never caught on like the GIA system for diamonds, his system was actually pretty good.

The system described depth of color on a scale from 0-100 with 0 being colorless and 100 being so dark as to be black. As I recall (and it has been many years now), the system put a premium on rubies somewhere in the 70-80 grade as to depth of color. So, rubies should be a relatively dark color.

One thing to note is how the intensity of sunshine will create a variance in how dark a ruby appears. In the bright tropical sunshine of Bangkok, a ruby will tend to look lighter than the same stone in North America. A good looking stone in BKK may well look way too dark here in the USA.

Recognizing color overtones in rubies

Now we have to deal with what I call overtones. There are some color overtones which will generally downgrade most gemstones, in particular, gray and brown. These two colors, as overtones, will generally downgrade diamond, sapphire, amethyst, garnet and so on.

In the case of rubies mined in Thailand, there can be a tendency for a purple overtone, which is a downgrade for ruby. In fact most any deviation away from red itself is a downgrade for ruby. However, in the case of Burma ruby when there is an overtone it often happens to be pink. Pink is generally a color that people like. But here we get into regional differences.

Through the years, very slightly (and I mean very slightly) pinkish ruby has been greatly appreciated in Japan. In Germany, they prefer a very dark but pure red ruby. Meanwhile here in the USA, we tend to prefer dark pure red, but not as dark as in Germany. The most aware and canny ruby merchants in Thailand will divide their stock up according to which country’s customers are showing up on a given day. As the internal consumption for ruby grows in the BRIC countries it will be fun to see which preferences for the color of ruby create a trend in which country.

It’s all about the chemistry

Above we mentioned that ruby is “red corundum.” Well, what is corundum? Corundum is an oxide of aluminum in a crystal form. So, ruby is pretty much aluminum and oxygen. Its chemical formula is: Al203.

What makes ruby different than the other colors of corundum (known as sapphire) is the addition of chromium to the chemical mix. As a matter of fact, there have been some red corundum gems that had an unusual color of red as compared with ruby. These gems had a slightly brownish overtone. When an analysis of these gems was made it was discovered that they were colored not by chromium but by iron. Then the issue became whether they were ruby (red corundum) or sapphire (red corundum colored by iron). In the long run it was decided by the gemology world that these gems should be labeled as red sapphire since there was no chromium present. So, in the world of modern gemology, ruby must have its color created by chromium in order to be labeled as ruby.

Asterism: the star ruby

One fun fact about ruby is that a certain small percentage of rubies are given to asterism. Asterism is the phenomenon that gives us “star” gems—gems which, when subjected to a strong single source of light show a star-like pattern. In order for the star to be visible, the stone must be cut as a cabochon with either a round or an oval silhouette. Natural star rubies are exceptionally rare. Natural star rubies from Burma are even more rare.

Asterism is caused by micro-crystalline inclusions of rutile. Rutile is a mineral on its own and is titanium dioxide. It is fairly commonplace for rubies to have an amount of these crystalline inclusions somewhere in the stone but not enough to make a star. In these instances gems are often heat treated in a way that causes the rutile crystals to simply melt into the rest of the ruby and create better clarity in the resulting gem. In fact a good percentage of the gems which a few decades ago would have been cut as star gems are routinely heated into transparent faceted stones. As a result the already rare Burmese star rubies are even more rare than ever.