What’s the Difference Between “Heated” and “Unheated” Gemstones?
When purchasing colored gemstones, especially rubies and sapphires, the terms “heated” and “unheated” are often mentioned. So, what exactly do “heated” and “unheated” refer to? What are their differences? Let’s explore this today.
What is “Heating”?
In fact, the natural formation of gemstones is a “heating” process.
Except for diamonds and peridots, which form in the Earth’s mantle, other gem minerals form in the crust. They undergo high-temperature and high-pressure heating deep in nature before becoming gemstones.
“Heated (old heating)” means the gemstone has only undergone artificial high-temperature heating, while “unheated” means the gemstone is natural and has not been heated.
Heating involves placing the gemstone in a controlled heating device, applying different temperatures and conditions to improve its color, transparency, clarity, and other characteristics in a long-term stable manner, thereby enhancing its aesthetic and commercial value.
For example, Sri Lankan sapphires, after heating, change from light blue to deep blue. However, both “heated” and “unheated” sapphires are indistinguishable to the naked eye—laboratory equipment is required to tell the difference, meaning their appearances are identical.
In simple terms, heating a gemstone is like adding a finishing touch: heated gemstones are more beautiful and still hold collectible value and appreciation potential. Many gemstones at auctions are also heated.
What truly matters is that “heated” gemstones are divided into “old heating” and “new heating.” Only “old heating” (simple artificial heating) is accepted by both domestic and international gemological laboratories as an optimization method; such gemstones retain commercial value and are classified as natural. In contrast, “new heating” (adding chemical elements before heating) is not accepted, significantly reducing the gemstone’s value.
Why Heat Gemstones?
In reality, natural gemstones almost always have inclusions during their formation, yet everyone desires to purchase vibrant, clear, and flawless gemstones.
To maximize market appeal, gemstones are optimized—heating is one of the most common methods.
Raw Gemstones Before Processing
Generally, most gemstones from mining areas undergo heating optimization, with two exceptions: gemstones of such poor quality that heating is not worth the effort, or gemstones already perfect in their natural state.
Heating optimizes gemstones to achieve a more perfect state, as high-quality “unheated” natural gemstones are becoming increasingly rare due to:
- Declining Quality of Gemstones from Mines
At many domestic and international jewelry exhibitions, buyers seek high-quality gemstones, but their availability has decreased compared to previous years. Any gemstone that meets criteria (high color saturation, clean to the naked eye, excellent cut with full brilliance) commands soaring prices! At auctions, high-quality collectible gemstones repeatedly set new record prices. - Increasing Difficulty in Sourcing Gemstones
Sourcing high-quality, large-carat sapphires is extremely challenging. This is especially true for 3–5 carat, unheated sapphires from renowned origins like Sri Lanka or Myanmar, which are now exceptionally rare.
Even if such gemstones are found, upstream miners and dealers are reluctant to sell them without a sufficiently high offer, as their own extraction difficulties continue to rise.
- Scarcity and Uniqueness of Gemstones
Gemstones are non-renewable mineral resources. Unlike consumables like luxury cars, their value does not diminish over time. Instead, as mineral resources deplete, their rarity becomes more pronounced, and their value continues to grow.
Heating optimizes gemstones to achieve two results: altering their color or reducing the visual impact of internal inclusions. This process is roughly similar to what gemstones undergo in nature—only the timeframe differs.
Which Gemstones Are Commonly Heat-Optimized?
Beyond rubies and sapphires, heat optimization is frequently used for:
1. Amber
Submerging amber in hot oil deepens its natural color. This process also enhances clarity, and the hot oil may create a series of shimmering, lustrous inclusions.
2. Aquamarine
Most aquamarines have a greenish tint without heat treatment; heating removes this to produce a purer blue.
3. Amethyst
Heating can eliminate brown inclusions in amethyst or lighten overly dark stones. Some amethysts can be transformed into citrines through heating.
4. Tanzanite
Low-temperature heating removes brown tones, revealing a more vibrant violet-blue hue.
5.Topaz
Heating pinkish-yellow topaz removes yellow tones, intensifying the pink. It can also adjust the shade of blue topaz to achieve various blue hues.
Most pink-to-red topaz sold on the international market today is derived from yellow or orange topaz through heat treatment.
When Buying Gemstones…
Whether a gemstone is “heated” or “unheated” is not the most critical factor. In fact, the key considerations for purchasing gemstones are similar to those for diamonds: primarily clarity, color, cut, and carat size.
If a gemstone has stunning color, high clarity (e.g., “pigeon’s blood” in rubies, “cornflower blue” or “royal blue” in sapphires), a perfect cut, and appropriate size—whether “heated” or “unheated”—it is worth buying.
