Gemstone Treatments: How Chemical and Thermal Processes Enhance Jewelry

Gems that make it to display cases have often undergone procedures to enhance their color, brilliance, and durability. These treatments, standardized by the American Gem Trade Association (AGTA), help make rough stones more appealing and durable, in addition to ensuring a consistent supply for the jewelry market.

What Are Gemstone Treatments and Why Are They Applied?

A treatment is any intervention—excluding cutting and polishing—intended to improve a gemstone’s appearance, durability, or availability. Some of the most common reasons include:

• Aesthetic Enhancement: Processes like heating, dyeing, and coating can intensify or even out color, boosting a gem’s visual appeal.
• Increased Durability: Techniques like fracture filling and impregnation strengthen the stone’s structure, reducing the risk of chips and scratches.
• Meeting Market Demand: Treatments allow for the creation of shades and effects that are rare in nature, expanding a jeweler’s portfolio.
• Material Salvage: Stones that would otherwise be discarded become commercially viable after gaining color or clarity.

Key AGTA Codes and Their Meanings

The AGTA uses letters to indicate the method applied. Here are some of the most common ones:

• H – Heating: Heat treatment used to alter a gem’s color and/or clarity.
• B – Bleaching: Whitening a gem using light or chemical reagents.
• D – Dyeing: Introducing dyes to create or intensify a gem’s color.
• F – Filling: Filling fractures with a colorless glass or resin.
• I – Impregnation: Impregnating porous gems with plastics to reinforce their structure.
• R – Irradiation: Exposing a stone to radiation, often followed by heat, to change its color.
• L – Lasering: Using a laser and acids to remove inclusions, especially in diamonds.
• ASBL – Assembled: A piece formed from layers of natural and/or synthetic materials.

A complete list of codes is available on the website of the Gemological Institute of America (GIA), an international reference in gemology.

Impact on Value and the Need for Disclosure

In the collector’s market, gems that are completely untreated tend to fetch higher prices due to their rarity. However, well-executed treatments increase the commercial value of stones that were once less attractive, offering competitive options for consumers who prioritize appearance.

In the United States, the Federal Trade Commission requires jewelers to clearly disclose any treatments that might influence a gem’s price or durability. Transparency builds customer trust and prevents future disputes. According to the AGTA, the sales tag should include the treatment code and, if necessary, specific care instructions.

How Consumers Can Protect Themselves

Experts recommend asking for a gemological certificate that details any treatments. It’s also wise to check if the jeweler follows the standards of the AGTA or an equivalent body in your country. This way, the consumer knows the stone’s history and can evaluate whether the price aligns with the level of intervention it received. For those who plan to resell or collect, independent certificates are essential, as some processes—like dyeing or coating—can fade over time, affecting the stone’s resale value.

After-Purchase Care

Even though treatments can increase durability, some gems require specific maintenance. Oils, harsh detergents, or excessive heat can compromise fillings and dyes. It’s recommended to clean jewelry with a soft cloth and, whenever possible, take it to a professional for periodic check-ups.

Understanding how a gemstone has been enhanced helps consumers make more informed choices, preserving both the gem’s sparkle and their investment for years to come.

Image Credit: Stuller Blog