An example of diffusion treatment with color concentration ring around the girdle. Courtesy of “Working with Gemstones: A Bench Jeweler’s Guide”.
An example of a stone benefiting from advancements in treatments is the sapphire. While the sapphire is more commonly known to be heat treated, diffusion has become another method of enhancing the gem.
In current markets, sapphires are routinely heat treated. This practice is performed by baking sapphires anywhere from low to high temperatures until their top color is produced. While intensifying the color is the main purpose of heating sapphires, it can also help remove inclusions and improve their transparency. Heat treatment is beneficial because previously unsellable material, due to either color or clarity, can be improved and sold.
Heat treatment is durable and will maintain the stone’s color as long as the stone is handled with normal care. If tested by a gemological lab, such as GIA or AGL, it will note heat treatment and state it’s common practice for sapphires.
While heating is normal for sapphires, diffusion takes the heat process one step further. There are two types of diffusion: traditional and lattice. The introduction of outside chemical elements separates diffusion from standard heat treatment.
Traditional diffusion uses the addition of titanium and chromium to the heating process. Both of these chemical elements are natural coloring agents found in corundum and introducing them to the process helps enhance the color. Diffusion is a popular use for blue sapphires because of the resulting rich color.
Diffusion is performed by packing these chemical elements on the stone’s surface and heating the stone. As a result, a thin layer of rich color is developed inside the gemstone. However, the color treatment does not fully penetrate the stone. While the color is stable, even after the use of a jeweler’s torch, if the stone is chipped or scratched it can result in a dead spot of color.
Detection of this treatment can be determined by a few different methods. The most efficient is testing by a trusted gemological lab. However, using a diffused white light or submerging the stone under water, you will notice concentrations of color around the facet junctions.
According to GIA, in 2003 a new type of diffusion treatment began to appear. Since traditional diffusion wasn’t successfully penetrating the entire stone with color, experiments with other elements began. Once again, strong color blue sapphires filled the market. After more research, diffusion was suspected again. However, a new element was used which changed this process altogether.
This new chemical element was beryllium. It transformed diffusion process because of its atomic structure. Since beryllium has a smaller atom than titanium and chromium, it allowed the entire stone to be diffused with color. Large blue sapphires, as well as yellow and orange sapphires, were now successfully undergoing color change, known as lattice diffusion.
Much like traditional diffusion, lattice diffusion is considered permanent and doesn’t require any special care. Detecting it is more difficult because it penetrates the entire stone. Gemological labs are the best source for identification of this testing. While there is still research being done on this treatment, it is important to keep up with industry news in the event new information is developed.
A book I highly recommend for all jewelers is “Working with Gemstones: A bench Jeweler’s Guide” by Arthur Anton Skuratowicz and Julie Nash. This guide provides detailed information of various treatments, the stones they are used on, and how to take care of them. This will help with more in depth information about heat, diffusion, and other treatments used on color gemstones.
Konrad Darling is the sales and marketing director for Darling Imports, a color gemstone wholesaler offering genuine and synthetics as well as lapidary services and stone identification. For more information contact Darling Imports at 800-282-8436 or www.darlingimports.com.
