Amethyst is a popular semiprecious gemstone renowned for its beautiful purple color. This violet hue sets amethyst apart from other quartz varieties and is highly desired by jewelry lovers and collectors alike. However, some people wonder if the purple color of amethyst can fade over time, especially with exposure to light or heat. In this article, we’ll explore whether the purple from amethyst actually fades and what factors can affect the color stability of this gem.
What Causes the Purple Color in Amethyst
The purple color of amethyst is caused by trace amounts of iron within the mineral structure of quartz. Specifically, irradiation and the presence of iron impurities lead to the formation of iron-titanium positive hole centers in the crystal lattice of quartz. This process results in the characteristic purple to violet hue seen in amethyst gems.
The iron-titanium positive hole centers absorb light in the yellow region of the visible light spectrum. This selective absorption leaves the complement color violet to be reflected back to our eyes, creating the purple color we see. Therefore, any changes to these color centers through exposure to radiation, heat, or other processes can lead to color shifts in amethyst over time.
Does Sunlight Exposure Cause Fading?
Direct and prolonged exposure to sunlight can potentially cause the purple color of amethyst to fade to a lighter, paler shade. The ultraviolet (UV) radiation in sunlight has high enough energy to disrupt the iron-titanium color centers in the amethyst crystal structure. This disruption reduces the gem’s ability to selectively absorb yellow light, resulting in a lighter purple or faded color.
However, the degree of color change from sun exposure depends on several factors:
- Intensity and duration of light exposure
- Original depth of color saturation
- Presence of color zoning in the gem
- Whether the amethyst is faceted or polished versus raw
In general, amethyst gems with a deeper, more saturated purple color are less likely to exhibit major fading with sun exposure. Paler stones and surface zones can fade more noticeably. The orientation and faceting of cut amethyst can also minimize light penetration and color shifts.
Does Heat Treatment Cause Fading?
Most commercial amethyst undergoes heat treatment to improve color saturation and remove undesirable brownish hues. This heating process permanently alters the iron-titanium color centers, so treated amethyst does not fade any further with sun exposure or other ambient heat over time.
However, some low quality heating processes can leave amethyst more prone to fading with light exposure. Too much heat or imprecise temperature control can partially disrupt color centers instead of stabilizing them. So responsibly heat-treated amethyst should be color-stable, while some commercial treatments may create problems.
Effects of Cleaning, Irradiation, and Chemicals
Cleaning solvents, irradiation, and chemical exposure can also impact the color stability of amethyst:
- Cleaning: Soaking amethyst in ultrasonic cleaners or harsh solvents can cause subtle lightening over many cleanings. Gentle dish soap and water is safest.
- Irradiation: Amethyst can be artificially irradiated to enhance purple color, but this is not permanent. The improved color will eventually fade with light exposure.
- Chemicals: Prolonged chemical exposure, especially to acids, can damage or disrupt color centers and cause fading.
Oils, dirt, and debris on the surface of amethyst can also make the color appear duller until cleaned. So while cleaning is recommended, harsh chemicals and excessive irradiation should be avoided.
Does Heat Fading Happen with Worn Amethyst Jewelry?
There is very little risk of color fading in amethyst jewelry due to body heat or ambient environmental temperatures. The small amount of heat generated from wearing or storing amethyst rings, pendants, bracelets, etc. is well below temperatures that could alter the gem’s color centers.
Even in very hot climates or during strenuous activity, the heat transfer from amethyst jewelry touching the skin does not get high enough to cause concerns of heat fading. The only exceptions would be very prolonged exposure to high heat, like in a kiln or furnace, which never happens in normal wear and use.
Testing for Color Stability
Gemological laboratories like GIA and AGS test amethyst specimens and provide color stability assessments along with other identification reports. These independent analyses grade gems on their likelihood to exhibit fading or color shifts from light, heat, and other factors.
Jewelers may provide these lab reports to customers looking for extra assurance about expensive amethyst pieces. In general, responsibly sourced amethyst with no signs of instability on reports can be expected to maintain its rich purple tones over many years of enjoyment.
Preventing Amethyst Color Fading
While amethyst color fading is not extremely common, especially from ambient environmental factors, there are some steps you can take to safeguard your gem’s vibrant purple hue:
- Avoid prolonged sun exposure – store amethyst jewelry in boxes when not worn
- Remove amethyst rings and bracelets before cleaning, swimming, yardwork, etc.
- Use mild dish soap and water to clean – avoid harsh chemicals and ultrasonic cleaning
- Keep away from high heat sources like stoves, space heaters, etc.
- Have important amethyst pieces periodically re-checked by a gemologist
Taking basic precautions allows you to enjoy your amethyst jewelry for years without significant color change. With proper care, the mesmerizing purple that makes this gem so appealing will remain saturated and vibrant.
How is Amethyst Color Change Value Assessed?
If a piece of amethyst jewelry does exhibit some fading or lightening of color over time, how the change in value is assessed depends on multiple factors:
|Degree of Color Change
|Subtle shifts may not affect value, while major fading can lower value significantly
|Cause of Change
|Fading from damage vs. natural causes may be appraised differently
|Well-cut gems retain appeal better than poor cuts when color declines
|Fading may matter less in designer vs. precious metal settings
|Special amethyst specimens with rare features can retain value well
In many cases, the gemologist or appraiser may recommend re-cutting or re-polishing the amethyst to improve the faded color. Incremental color change in high quality pieces may not impact value. But consumers should be aware of whether the color instability was natural or caused by poor handling when assessing any value changes.
Does Amethyst Ever Change Color Completely?
In extremely rare circumstances, amethyst can shift from purple to yellow, green, or even colorless. These drastic color changes require extremely high heat, well above temperatures the stone would ever encounter during jewelry use and wear. The conditions needed to make amethyst change color entirely only occur in volatile geologic processes deep underground.
Partial decolorization can also stem from prolonged exposure to intense light sources over many years in unique laboratory settings. Amethyst jewelry will never spontaneously change to a completely different color without obvious severe damage from unnatural circumstances.
So while major amethyst color changes make for interesting geologic and gemological knowledge, consumers do not have to worry about a beloved purple amethyst turning yellow or green overnight. Color stability can be trusted within normal boundaries of use.
Amethyst deserves its reputation as an alluring and regal purple gemstone that makes stunning jewelry. While excessive light, heat, and irradiation can potentially cause the purple color to fade, this is unlikely to happen with normal jewelry use and care. Responsibly sourced, well-cut amethyst of medium to deep purple tones remains reliably stable over time. With some basic precautions to avoid sun damage, heat, and chemicals, the vibrant violet color in amethyst can be cherished indefinitely.