Heated vs Un-heated Sapphires: What You Need to Know

Sapphire heat treatment is an accepted practice in the gemstone industry. It is a process that involves placing rough sapphires in extremely high temperatures for several hours to improve their color and clarity. The specific temperature and duration of the treatment can vary based on the unique characteristics of the rough sapphire being treated. This process can be carried out using either gas-powered or specially-built electric ovens. It is estimated that approximately 90% of sapphires available in the market have undergone heat treatment. While some may argue that this process diminishes the value of the gemstone, it is a widely accepted practice that has been used for many years to enhance the beauty of sapphire gemstones.

The history of sapphire heat treatment

The heat treatment of sapphires is not credited to a specific inventor, as it has been practiced for centuries by gemstone cutters and traders. The technique is believed to have been discovered accidentally when sapphires were exposed to high temperatures during the process of soldering jewelry. Since then, gemstone cutters and traders have experimented with various heating methods to improve the color and clarity of sapphires, leading to the development of the heat treatment process commonly used today.

In the past few decades, gem traders in Thailand turned the heat treatment of sapphires into a highly profitable venture. They purchased large quantities of low-quality rough sapphires from Sri Lanka and enhanced their color and clarity through heat treatment. Eventually, gem merchants in Sri Lanka began adopting the practice and developed their own ovens to carry out the heat treatment process. Today, many successful gem merchants in Sri Lanka are those who pioneered the heat treatment process. The "Lakmini Furnace" is one of the most well-known ovens used in Sri Lanka for heat treatment of sapphires. The heat treatment process has become a standard practice in the sapphire gemstone industry, and it has helped to enhance the value and beauty of many gemstones.

Are heated sapphires of inferior quality compared to unheated sapphires?

Actually, the opposite is true. If we focus solely on their characteristics and ignore the fact that heated sapphires have been artificially altered, they are superior to unheated sapphires. However, in the gemstone trade, unheated sapphires command a premium price due to their rarity. Heat treatment greatly enhances the color and clarity of sapphires. It is challenging to find a sapphire with the same quality as a heat-treated sapphire, which is why unheated sapphires can cost twice as much as heated ones.

Why un-heated sapphires are so expensive

Heated sapphires exhibit darker hues and better saturation, thanks to the high temperatures used in their treatment process. This heating process also eliminates impurities in the stone, resulting in enhanced clarity. Additionally, trace elements are more evenly distributed throughout the stone, giving heated sapphires a more uniform color and overall appearance. These effects combine to make heated sapphires exceptionally beautiful.

It is rare to find all of these favorable characteristics in a natural environment. To obtain such a sapphire, the crystal must grow in a very special environment, which is an extremely rare occurrence. Consequently, unheated sapphires that possess strong saturation, high clarity, and exceptional luster are highly prized and command a premium price.

How to identify un-heated sapphires

Gemmologists can easily differentiate between heated and unheated sapphires by examining the stone under a microscope and analyzing the inclusions. However, the characteristics of inclusions can vary depending on the origin of the sapphire, so a gemmologist with experience in a specific type of sapphire, such as Ceylon sapphires, will be better equipped to identify its treatment status.

In some cases, it may be challenging to distinguish between heated and unheated sapphires. For instance, if the stone has been lightly heated, the inclusions may not have been significantly altered, making it difficult to identify. Additionally, some rare sapphires are so clean that there may not be enough inclusions to observe a difference. In these cases, a gemmologist may not be able to determine whether the stone is heated or unheated and will likely avoid making a judgement.