Gemstone Education: Sapphires - Treatment

Sapphire Treatments: Enhancing Beauty and Color

Sapphires, members of the corundum family, undergo treatments to enhance their color and clarity. Two common methods are lattice diffusion and heat treatment, each with specific effects on the appearance and properties of these gemstones.

Lattice Diffusion

• Objective: Lattice diffusion is a treatment process where certain elements are introduced into the atomic lattice of a gemstone during heat treatment to change or enhance its color.
• Process and Elements: Initially, experiments in the 1980s focused on diffusing titanium and chromium (natural coloring agents in corundum) but met with limited success in fully penetrating the stones. A breakthrough occurred in 2003 with the introduction of beryllium diffusion. Beryllium atoms, being smaller than titanium or chromium, can penetrate the entire depth of the gemstone, even in large sapphires, effectively altering their color throughout.
• Impact on Sapphires: Beryllium diffusion is capable of enhancing the color of sapphires, intensifying existing colors or inducing new ones.

*images courtesy of GIA. Used with permission.

Heat Treatment

• Purpose: Heat treatment is employed to alter the color and clarity of corundum gemstones.
• Effects on Sapphires: Heating sapphires can intensify or induce blue coloration. It also removes silk inclusions, enhancing the gemstone’s clarity and transparency. Like rubies, the recrystallization of silk can improve asterism in sapphires.

*images courtesy of GIA. Used with permission.

Considerations and Care

• Durability and Stability: While these treatments can significantly enhance the gemstone's aesthetic qualities, they may affect its durability and require specific care, particularly avoiding environments that could reverse the treatment effects, such as extreme heat or certain chemicals.
• Impact on Value: Sapphires that have undergone heat treatment or lattice diffusion are valued differently that untreated sapphires. Within the industry, heat treatment for sapphires is ubiquitous and considered to be standard. On the other hand, lattice diffusion is like heat treatment with additional color-enhancing properties, and is not considered standard. Because of this, sapphires that have undergone heat treatment only are substantially more valuable than comparable looking sapphires that have undergone lattice diffusion. Furthermore, sapphires that are treatment free (often referred to in the trade as “No Heat”) are rare and can be highly valuable.
• Disclosure: Due to the meaningful impact on value, it is crucial for sellers to disclose these treatments to buyers. Furthermore, they can affect the gemstone's care requirements.