Gemstone Color Enhancement: Natural vs Treated Stones

Most gemstones on the market today have been treated to enhance their color, clarity, or both. Understanding these treatments helps you make informed purchases and care for your jewelry properly.

Common Treatment Types

Heat Treatment

The most widespread and accepted treatment. Gemstones are heated to high temperatures to improve color and clarity. This treatment is permanent and does not require special care.

• Sapphires: Heat deepens and evens out blue color. Over 90% of sapphires are heated
• Rubies: Heat improves red color and reduces purple or brown tones
• Tanzanite: Nearly all tanzanite is heated to transform from brownish to blue-violet
• Aquamarine: Heat removes greenish tones for a purer blue
• Citrine: Most citrine is actually heat-treated amethyst

Irradiation

Exposure to radiation changes or intensifies color. Often combined with heat treatment.

• Blue topaz: Nearly all blue topaz is irradiated. Natural blue topaz is extremely rare
• Colored diamonds: Some blue, green, and yellow enhanced diamonds are irradiated

Fracture Filling

Surface-reaching fractures are filled with glass, resin, or oil to improve clarity.

• Emeralds: Almost all emeralds are oiled or filled. Cedar oil is the traditional treatment. This is considered standard practice, but heavily filled stones are less valuable. See our clarity guide
• Rubies: Glass-filled rubies (composite rubies) are significantly less valuable than untreated

Diffusion Treatment

Chemical elements are diffused into the stone at high temperatures to add color.

• Sapphires: Surface diffusion adds blue color. Deeper diffusion (beryllium) can produce yellow, orange, and padparadscha colors
• Important: Diffused color may be affected by recutting or repair

Coating

A thin layer of material applied to the surface to change or enhance color.

• Topaz: Mystic topaz has a rainbow coating on the pavilion
• Note: Coatings are the least durable treatment. They can scratch and wear off

How Treatments Affect Value

• Accepted and expected: Heat treatment, emerald oiling — minimal impact on value
• Moderate impact: Irradiation, beryllium diffusion — should be disclosed, somewhat lower value
• Significant impact: Glass filling, heavy fracture filling, coating — substantially lower value
• No treatment (untreated): Commands the highest prices, especially for rubies, sapphires, and emeralds

Disclosure Requirements

Reputable sellers must disclose all treatments. In the US, the FTC requires disclosure of any treatment that:

• Is not permanent
• Requires special care
• Significantly affects value

Always ask about treatments when purchasing. A reputable seller will provide this information freely.

Care Considerations by Treatment

• Heat-treated: No special care needed. The treatment is permanent
• Oiled emeralds: Avoid ultrasonic cleaners and steamers. Use only warm soapy water. See our care guide
• Glass-filled: Very fragile. Avoid chemicals, heat, and ultrasonic cleaners
• Coated: Clean only with a damp cloth. Avoid any chemicals or abrasion
• Irradiated: No special care needed. The treatment is stable

For more on gemstone treatments, read our detailed treatment guide. Shop gemstone jewelry at Biovlia with complimentary shipping.