Heat Treatment Of Sapphire

What Are Heated Sapphires? 

Heated sapphire is a natural sapphire gemstone that has undergone controlled heat treatment to improve its colour and clarity. This process has been practiced for more than a thousand years and is widely accepted in the gemstone industry. 

Sapphires are varieties of the mineral corundum, composed mainly of aluminum oxide, and they occur naturally in many colors, including blue, pink, yellow, green, and white. 

However, many sapphires mined from the earth may appear dull, pale, or cloudy. Heat treatment enhances their appearance, making them more vibrant and visually appealing for jewelry.

The Heating Process 

The heating process usually involves exposing the sapphire to temperatures ranging from 1,500 to 1,800 degrees Celsius in specialized furnaces. During this process, silk & other inclusions inside the gemstone may dissolve & become less visible, creating gems with better transparency. 

A pale blue sapphire can become a rich royal blue after treatment. It can do this by dissolving titanium or iron rich rutile needles. These impurities are then forced to diffuse into the crystal structure. 

Heat can also remove unwanted colour tones, such as gray or brown, resulting in a cleaner and brighter gem. 

Low-Temperature Heat treatment 

Sometimes lower temperatures are used to treat gemstones of around 500 degrees celsius. This method is often used for more delicate stones as it is less likely to fracture stones with inclusions. Lower temperature heating is commonly used on pink sapphires. 

These lower temperatures do not induce as much change to the various inclusions within the corundum compared to higher temperatures. This means that there are fewer signs of detectable heat treatment when studied at the microscopic level. 

Heat treatment can produce a great improvement in the colour of pink sapphire by reducing tones of blue. 

Colour Zoning 

Heat treatments often result in a much more uniform colour, which makes the stone more desirable. 

Uneven colour zoning occurs when trace elements are trapped in uneven, patchy concentrations during the gems growth. 

The heating process causes the structure of the corundum to expand, encouraging the trace elements to be redistributed throughout the crystal lattice. 

An Appreciated Technique

Heated sapphires are extremely common in the jewelry market. In fact, the majority of sapphires sold worldwide have been heat treated. You can fairly safely assume that a sapphire you purchase has been heat treated & not an untreated natural sapphire, unless it specifically says otherwise. 

That being said, sapphire sometimes undergoes different types of treatment such as beryllium diffusion, fracture filling or irradiation. 

Jewelers and gem dealers consider heat treatment standard because it does not involve adding artificial materials to the stone. Unlike synthetic sapphires, heated sapphires are still natural gemstones formed within the earth. The treatment simply enhances qualities that already exist in the crystal.

Heating With A Flux 

Sometimes stones are heated alongside a flux, which melts & flows into the surface cracks and hardens. The mark these techniques leave behind is easily identifiable by lab analysis and can even be visible under UV lighting. 

This method is useful for repairing poorer quality stones & making them marketable, although it is not the most admired practice in the industry. These stones are less valuable than heated only stones of the same qualities. 

Yellow Sapphire 

Yellow sapphire is often heated because natural yellow sapphire’s colour is unstable and can lose its colour when exposed to sunlight. Heat treated yellow sapphire’s colour is stable. 

Untreated Sapphire

One reason heated sapphires are popular is affordability. Untreated sapphires with naturally vivid colour and excellent clarity are rare and therefore much more expensive. Heat treatment allows lower-quality stones to achieve a more attractive appearance at a lower cost. This makes sapphire jewelry accessible to a wider range of buyers. Consumers can enjoy beautiful gemstones without paying the premium associated with untreated stones. 

Durable Stones 

Despite their enhanced appearance, heated sapphires retain the same hardness and durability as untreated sapphires. Sapphire ranks 9 on the Mohs hardness scale, making it one of the hardest natural gemstones after diamond. Because of this toughness, heated sapphires are suitable for everyday wear in rings, necklaces, earrings, and bracelets. 

Treatment Transparency 

Transparency about treatment is important in the gemstone industry. Reputable jewelers disclose whether a sapphire has been heated because treatment affects the stone’s value. 

Untreated sapphires are generally considered more valuable due to their rarity, especially if they possess exceptional natural colour. 

Gemological laboratories can identify heat treatment using microscopic examination and advanced testing techniques. Heated sapphires often have characteristic inclusion patterns caused by the heating process. 

Some collectors and gemstone enthusiasts prefer untreated sapphires because they value natural beauty and rarity. Others are perfectly satisfied with heated sapphires because they offer beauty, durability, and affordability. Ultimately, the choice depends on personal preference and budget.