TREATMENTS
Heated vs Unheated Gemstones
The single most important factor affecting gemstone value after color. Understanding heat treatment—what it is, why it's done, and how to verify it—is essential for any serious collector or investor.
90-95% of sapphires and rubies on the market have been heat treated. Unheated stones command premiums of 20-100%+ depending on quality. For investment purposes, unheated is strongly preferred.
What is Heat Treatment?
Heat treatment is exactly what it sounds like: gemstones are heated to high temperatures (typically 800-1800°C) to improve their color and/or clarity. This is the most common treatment applied to sapphires and rubies.
The process can dissolve silk inclusions (improving clarity), intensify color saturation, or shift color entirely (turning pale stones more vivid). It's been practiced for centuries and is considered a permanent, stable enhancement.
Heat treatment is industry-accepted and legal—but it must be disclosed. The problem is that disclosure is inconsistent, especially in retail jewelry where "natural" is often used loosely.
Why Does It Matter?
From a purely visual standpoint, a well-heated stone can look identical to an unheated one. So why pay more for unheated?
Rarity: Unheated stones with fine color are genuinely rare—perhaps 5-10% of the market. Nature rarely produces the perfect combination of color, clarity, and crystal structure without human intervention.
Authenticity: An unheated stone is exactly as nature made it. For collectors, there's inherent value in owning something untouched by human modification—a piece of geological history.
Investment: Unheated stones hold value better and appreciate more consistently. The market for unheated material is driven by connoisseurs and institutions, not casual buyers—a more stable collector base.
Types of Heat Treatment
Not all heat treatment is equal. The gemological community distinguishes between several types:
Traditional Heat (No Additives)
Simple heating without adding any foreign materials. This is the most accepted form of treatment. Labs will note "heated" or "H" on certificates. Value impact: moderate (20-50% less than unheated).
Low-Temperature Heat
Gentle heating (below 1000°C) that improves clarity without significantly altering color. Some labs distinguish this from high-temperature treatment. Generally more accepted than aggressive heating.
Beryllium Diffusion
Heating with beryllium to create or enhance color. This can turn worthless material into seemingly fine stones. Heavily impacts value—beryllium-treated stones are worth a fraction of natural or traditionally heated material. Avoid for investment.
Glass Filling (Rubies)
Lead glass is used to fill fractures in low-quality rubies, dramatically improving apparent clarity. These "composite rubies" are not stable—the glass can deteriorate with heat or chemicals. Never invest in glass-filled rubies.
How to Verify Treatment Status
You cannot reliably determine treatment status by eye—even experienced dealers can't. The only way to know for certain is through laboratory certification.
Major gemological laboratories use advanced spectroscopy and microscopy to detect signs of heating. They look for:
- Altered inclusion characteristics (dissolved silk, stress fractures)
- Modified crystal structure visible under magnification
- Trace element distributions inconsistent with natural formation
- Spectroscopic signatures of heat exposure
Treatment by Gemstone Type
Treatment prevalence varies significantly by gemstone type:
| GEMSTONE | % TREATED | UNHEATED PREMIUM |
|---|---|---|
| Sapphire | 90-95% | +20-50% |
| Ruby | 95-99% | +50-100% |
| Padparadscha | ~99% | +100-200% |
| Spinel | <1% | N/A (almost never treated) |
| Emerald | ~99% | +30-50% (for oil-only) |
Note: Emeralds are typically oiled rather than heated. "Minor oil" is accepted; heavy treatment is not.
The Spinel Advantage
Spinels deserve special mention here. Unlike corundum, spinels are almost never treated—their crystal structure doesn't respond well to heating. This means when you buy a spinel, you're almost certainly getting an untreated stone.
For collectors who prioritize natural, unenhanced gemstones, spinels offer what sapphires and rubies often can't: certainty without paying unheated premiums. Read more in our Spinel Buying Guide.
Our Position
At The Sapphire Bank, we strongly prefer unheated gemstones for our collection. Every stone we acquire comes with certification from a major laboratory confirming treatment status.
We believe unheated stones represent better long-term value. They're rarer, more desirable to serious collectors, and backed by our 12-month buyback guarantee.