Untreated Sapphires

The heat treatment of sapphires is one of the most common enhancement techniques in the gem industry today and generally regarded as stable, however, diffusion enhancement, a technique that improves color by introducing chemicals into the surface of the gemstone is not.  Both techniques improve the color and clarity of pale, included or lifeless stones and make a great deal more attractive product available to a wider market.  So when you are looking for a sapphire, why should you consider an untreated stone?

While heat treatment is considered to be a stable process, meaning that your gemstone should not change substantially in appearance over time, it's important to remember that the sapphires exposed to this process are heated to a temperature of over 2000 degrees Celsius, almost the melting point of sapphire, inducing permanent changes to the stone.  Diffusion enhancement adds chemicals to the cooking pot before the gemstones are heated, the chemicals are then introduced into the surface of the stone as it begins to break down near 2000 degrees.  Diffusion enhancement of a sapphire is not possible without heat treatment.

Because diffusion enhancement treats only the surface of the gemstone, it leaves the sapphire subject to abrasion, especially if it's used in a ring.  Oftentimes, areas of material may be removed due to normal daily wear and tear leaving your gemstone scratched or with a patchy, unattractive appearance.  Obviously diffusion treated sapphires are best avoided but this treatment is virtually impossible to detect without the use of specific gemological test equipment.  However, diffusion enhancement requires heat treatment, therefore, if the gemstone has not been heat treated it could not have been subjected to diffusion enhancement.

Fortunately, the signs of heat treatment or the lack of it, are easy to detect and if you (or your gem dealer) know with certainty that your sapphire has not been heat treated then you can rest assured that it has not been diffusion enhanced.

So how do you determine if the sapphire has been heat treated or not?  Under magnification, almost all gemstones show signs of naturally occurring impurities and variations in structure that can tell us a lot about where and when the gem was formed.  These marks, often seen only with the aid of special gemological microscopes are called inclusions and it is the size, quantity, location and type of these inclusions that determine the value of the gemstone.

Virtually every natural, untreated gemstone will have some inclusions when examined under the microscope and very small inclusions will usually not have any impact on the value of the stone, in fact, it is typically the presence of these small inclusions that prove the stone to be natural and / or untreated.  Oftentimes, the type of inclusions found in the stone will also establish where the stone is from (called its origin) and in the case of many rare stones, having the stones origin certified by an independent gem laboratory can increase the value of the gemstone many times over.

As for sapphires, during their formation another mineral called rutile often forms thin strands within the sapphire.  These thin strands are called silk and are easily visible when an unheated sapphire is examined under the microscope.   In some cases there is so much rutile within the sapphire that it takes on a cloudy appearance even to the naked eye and it is these gemstones that are typically heat treated.  If a sapphire is heated to 2000 degrees the thin strands of silk begin to melt and disappear forming very tiny drops of melted rutile within the stone.  The small drops are usually invisible to the naked eye and make the gemstone appear to be much clearer.  The presence of intact rutile threads or unaltered crystal inclusions within the sapphire indicates that it has not been treated, while small drops of melted silk are a positive sign that it has.

Part of the appeal of a precious gemstone such as sapphire is that it has been created by nature, that it is something rare and beautiful and not the result of man's manipulation of his environment.   While many may consider the various enhancement techniques such as heating or diffusion to be just "a little improvement" on nature the fact is that for something to be considered rare, it must be limited in quantity and in its original condition.

But it's a big world out there and may people just don't feel this way about gemstones.  For those who don't care whether a stone has been enhanced or not there is a never ending supply of stones that have.  However many of us prefer a gemstone that has not been enhanced.  Unfortunately, the supply of untreated gems is small and always decreasing, treasure then when you find them.

For More Information on Sapphires:

Gem Library - Sapphire

Gem Collection - Sapphire

Submitted on: May 15, 2009 @ 8:20am