What is the Best Color for Blue Sapphire? Part 4

October 2nd, 2009 by James L. Sweaney, CGA, FGA. GG
2.97 ct. Ceylon Sapphire

I-17700, 2.97 ct. Ceylon Sapphire

Blue, the color of sky, ocean, peace and tranquility has long been associated with purity and wisdom. Blue colors dominate many forms of spiritual art. Cardinals of the Catholic Church, exemplars of chastity and celestial purity, often wore rings of blue sapphire.

Blue has always been an important color for mankind, so when we ask what is the best color for blue sapphires, we should consider several points of view.

From a personal point of view, the answer is easy– the best color of blue sapphire is the blue that excites you the most. We recently had a client who wanted a ring made with the darkest blue sapphire possible, so dark it seemed black in most lights. The good news is that ultra dark colors in most gemstones are usually very inexpensive.

Ultra Dark Blue Sapphire

Ultra Dark Blue Sapphire

Another client wanted only pastel tones– a good choice because the cost for very light blue sapphire is lower than darker stones, and the light tones can be very lively and sparkly.

Light Blue Sapphire

Light Blue Sapphire

Gem Trade Secret- The color appearance of many sapphires will darken when the gem is mounted!

On the scientific level, the richest most intense blues occur at the tonal level of 75 – 85 on a scale of 0-100, 85 being a point called the gamut limit. Blues darker than 85 rapidly lose their intensity.

From the point of view of the gemologist or gem grader, the stones which have a pure blue hue with no overtones, a tonal value of medium to medium dark (those that do not exceed the gamut limit), and a saturation level of “vivid” will get the highest grade for color. Of course, the grader also considers clarity and cut in assigning an overall grade for the gem.

The gemstone market preference generally follows grading and historic preferences as well as natural distribution and the scientific base. Well cut pure blue stones that are rich and intense with high clarity are the rarest in nature and have always been the most desirable and valuable of sapphires.

7 ct Ceylon Sapphire Ring

7 ct Ceylon Sapphire Ring

The philosophic or ethical point of view brings us to another question. Many sapphires are heat treated to improve their color and/or clarity. Should heated stones be valued the same way as unheated ones?

A Very Brief History of Heat Treatment

While we have historic records of various kinds of heat treatments of gems dating back many centuries, none of these appear to offer ways to significantly alter or improve sapphire or ruby. A Swiss professor developed high temperature corundum treatment during the 1920’s– apparently, his secrets then leaked to the gem fields of the Orient.

Examples of heated sapphires were first noted in gemological laboratories in the mid 1960’s, so we can assume that the practice was not widespread or particularly successful until a decade later with the Geuda phenomenon.

The rise of heat treatment truly began with a type of sapphire commonly found in Ceylon known as “Geuda.” This milky white semitransparent material was full of “silk”, which are fine inclusions of rutile, a titanium oxide mineral. Geuda was sometimes suited for making star stones, but whitish star stones were not especially valuable, and a lot of this material wouldn’t even yield a good star. What to do with all this hard won but relatively worthless raw material?

Somewhere in the 1970’s, with the advent of efficient high temperature ovens, someone discovered that this low value by-product of gem mining could be transformed by high temperature heating into beautiful and eminently SALEABLE sapphires. Many pieces were destroyed by the process but many of those that survived were gorgeous. This caused the Great Geuda Rush a stampede in which many fortunes were made by those fortunate enough to own or obtain Geuda rough on the cheap.

Geuda Sapphire, Before and After Heat

Geuda Sapphire, Before and After Heat

Simply put, the Geuda material is heated to just below its melting point, where the crystal lattice is expanded to it maximum and bonds between molecules are as “wide open” as they can be. The heat caused the silk to dissolve and release titanium into the crystal lattice of the sapphire. Titanium is the main cause of blue color in sapphire. The result is a gem that has been significantly enhanced in both clarity and color.

The good news is that the Geuda stampede brought a lot of beautiful reasonably priced material to the gem market. And, as time went on, heating techniques evolved so that virtually all the main production of sapphire and ruby marketed today has been enhanced or improved by heat treatments.

The bad news is that as heat treatment became common practice, it opened the door to fraud and misrepresentation.


In essence, the Geuda sapphire as well as other heated sapphires and rubies are a raw material that is “ripened” by the application of heat. Nothing added, nothing taken away.

In the last 30 years or so, we’ve seen various attempts to “add” coloring agents to sapphire and ruby. Surface diffusion and beryllium diffusion are the main culprits, along with glass filling/impregnation. Often, these “doctored” materials have been surreptitiously introduced into the marketplace with no disclosure, a highly fraudulent practice. For the most part, these treated stones are mediocre and readily detectable by trained gemologists.

The important thing, in this writer’s opinion, isn’t whether a gem has been heat treated or not, but rather that the fact of treatment is disclosed to the gem trader and especially, to the ultimate consumer. Consumers should be presented with all the facts, not only about enhancements, but also about quality of color, clarity, and cut, so that the new owner can make an informed choice when purchasing the gemstone.

The gem industry has developed the science to detect these treatments, available thru legitimate gemological labs around the world, and has several non-profit organizations such as the American Gem Trade Association, the American Gem Society, and the International Colored Stone Association, whose primary mission is consumer protection thru the dissemination of knowledge of gems, including their treatments, and the detection and disclosure thereof.

Market Value of Heated vs. Non Heated Sapphires

Beauty, durability, and rarity are the three pillars of value on which the price of a gemstone rests. By these criteria, sapphires enhanced by heat compare very favorably with non heated stones.

Many heated stones are significantly richer in color and higher in clarity than non heated stones– the whole point of heat treatment is to enhance the gemstone.

Durability has not been shown to be affected by heat treatment– stones that survive the process retain all the physical properties of sapphire.

While it is true that a gemmy crystal that is wonderfully colored and clear is much more rare than one that is not, it can also be truly said that all sapphire crystals are indeed rare in nature.

Within the gem market, small goods are generally assumed to be heated unless stipulated. Heat treatment begins to substantially affect the value of sapphires (and rubies) only in fine and extra fine qualities in larger sizes, and even then, only for ultra rare material such as the fabled Kashmir sapphire.

Generally, sapphires from Kashmir and Burma are not heat treated– these gems are extremely rare to begin with, so heat treatment is really a non factor when considering this material. Stones with documentation of these origins and lack of heat treatment are avidly sought by collectors and can fetch astronomical prices.

Most sapphires from Ceylon, Madagascar, Australia, Montana and other sources are routinely heated. Vendors of high end sapphires and rubies commonly document them thru legitimate gemological laboratories that are independent of the seller. For larger goods of fine to extra fine qualities, documentation of no heating can add substantial value, anywhere from 10 to 50% as a rule, much more for  Burma ruby.

A market has developed via the Internet for “Natural Sapphire,” touting the virtues of untreated sapphires as “pure, natural.” The implication is that heated sapphires and rubies are not natural and have somehow been defiled by the heat treatment.

Documentation of the lack of heat treatment, i.e. the natural-ness, is in many cases supplied by the vendor, rather than by independent gemological laboratories that have no vested interest in the grading or identification. The application of “soft heat” to many sapphires from Sri Lanka makes detection of heat treatment a real challenge, even for highly trained gemologists at the best independent laboratories.

To this writer, prices for the unheated goods commonly available on the internet seem to be very high for the quality offered.  Whether or not that market can sustain itself at its current price structure based on the primary virtue of no heat treatment remains to be seen.

We would certainly agree that doctored material such as the surface and beryllium diffused and glass filled material is not “natural”. Whether you can call a heat enhanced sapphire or ruby “natural” is a philosophical/semantic distinction.  The gemological community does not distinguish between “natural” and “unnatural” color, merely that the material is heat treated or not.

The gem market, for the most part, values sapphires, rubies and other heated gemstones, including tanzanite, imperial topaz, and aquamarine, primarily on their traditional merits, i.e. the quality of their color, clarity, and cut. Top end gems of larger size are the main exceptions to this rule. Legitimate vendors will always disclose these enhancements, along with other pertinent information.

As members of AGTA and AGS, we support and adhere to the code of ethics that calls for full disclosure of gem enhancements, as well as for honest, fair and thorough gem grading and representation. The professional gemologists at Mardon Jewelers are available to discuss the merits and characteristics of gemstones– Just give us a call or email, or stop by the shop.

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