Rubies are rare to begin with, and large, flawless ones are even more valuable than the very best diamonds. Historically, the best of these gems have come out of Myanmar (formerly Burma), but the United States Congress banned Burmese rubies in 2008. Since then, near-perfect rubies have become even rarer in the United States.
Since rubies are a Clarity Category 3 gemstone, they invariably carry some inclusions, or other materials caught inside the gemstone as the ruby formed around them. A ruby without any inclusions would be priceless. A ruby with only microscopic inclusions is very rare and valuable.
Star rubies contain an asterism, a silk-like substance trapped inside in the shape of a six-point, three-ray star. A ruby with a perfect asterism, with all six legs straight and forming a visible star, is extremely valuable and found only occasionally. Gemologists generally cut these stones in a half-dome shape to display the star. After cutting, the star appears to move across the surface of the gem.
Rubies are not generally very large, so their value increases with their weight. These gemstones formed from chrome beneath the earth's surface millions of years ago, and by its nature, chrome caused cracks within them. Very few rubies escaped this fate. A ruby larger than 3 carats is very rare, and the 27.37 carat stone auctioned by Sotheby's in 1999 is probably the only one of such size discovered to date. The larger the ruby, the more rare it is.
There are three types of ruby treatments available in the jewellery market:
Untreated
In the jewelry industry, it is assumed that rubies have been heat treated unless otherwise specified. These untreated stones are rarely encountered as only a handful of rubies in the world are untreated.
Large, clear rubies of good color that are untreated command extremely high prices and can only be found in the most expensive jewelry stores. When you see this word in a jewelry description, you can know that you’re seeing something rare (depending on the stone). If you see an “untreated” ruby for sale, it will be extremely valuable and expensive. Untreated rubies are almost always very included (unless they are in museums or with 6 digit price tags).
Colour is a ruby's most important feature. Its transparency is only of secondary importance. So inclusions do not impair the quality of a ruby unless they decrease the transparency of the stone. On the contrary: inclusions within a ruby could be said to be its 'fingerprint', a statement of its individuality and, at the same time, proof of its genuineness and natural origin. An untreated ruby is very rare, and an untreated stone with only minimal inclusions is more remarkable yet.
Top quality untreated rubies are so rare even the world's top gem dealers must incessantly comb estate sales and auctions to find them. Sizes above 3 carats are particularly rare. Almost all rubies are treated because most have inclusions. Treating the blemishes allows supply to keep up with demand. As a result, untreated rubies are usually museum-quality. Top dealers search for them, but few are available.
Conventional Heat Treatment
In the jewelry industry, it is assumed that rubies have been heat treated unless otherwise specified. The Gemological Institute of America and other certification authorities ACCEPT this treatment; it is permanent and will not degrade over time.
Over 99% of all Ruby on the market is heat treated, to stabilize and/or enhance the color and/or clarity. This is what you usually find in the market for rubies: Natural, treated, and with imperfect clarity.
This treatment can turn a colorless ruby into a blue ruby. At lower temperatures, silk can be improved and the color lightened. The typical heat enhancement procedure performed on Ruby from Sri Lanka (Ceylon) normally refers to the lower temperature wood 'blow' heat method, whereas and the typical heat enhancement procedure performed on Mogok, Myanmar, MongHsu, Thai, Vietnamese, and African Ruby usually refers to the high temperature furnace fired method. Both heating methods are accepted trade practices, and have been for many generations.
The heat treatment process is permanent and does not adversely affect the performance, and durability of the gem, but in recent years demand for natural non-heated non-treated top quality Ruby has caused these gems to command a somewhat higher premium, depending on the gem.
Heating With Flux:
This form of ruby treating was introduced in recent years. The conventional heat treatment for rubies helped to evaporate any gases present in the gem, it also helped to disintegrate some of the inclusions. The fissures and cracks present in the gem stone remained intact even after conventional heat treatment was applied to rubies. This flux heat treatment of rubies goes a step further to 'heal' the fissures and fractures present in the ruby. Borax based chemicals are used to function as flux. The addition of these chemicals into the oven helps reduce the melting point of the ruby. The molten ruby then seeps into the cracks and fissures in the gem stone. The cracks become invisible to the naked eye as the stone cools and solidifies.
Fissure Filling or Glass Filling
Corundum commonly comes from the mine with fractures (cracks). This is especially so in the case of rubies. These rubies are exposed to a high temperature for prolonged time periods. Once cooled, the rubies are actually filled with glass and therefore referred to as glass filled rubies. The transparency and color of these fissure (glass) filled rubies are enhanced with this process. These rubies offer buyers to indulge in large rubies at a lower rate than rubies with other treatment methods (or untreated stones).
| 
