What Is the Play of Color in Gems?
Color-changing gemstones are often favorites among jewelry-wearers and collectors alike. Play of color in gems gives the stones depth, radiance, and intrigue, adding that little bit of something extra to the gemstones.
While many people are mesmerized by the play of color in gems, it's also common to have questions about the phenomenon. What is play of color? Why does it happen? And what are the different types of play of color in gemstones?
Luckily, there are answers to each of the questions above. If you're curious about the play of color in gemstones, here's what you need to know.
What Is Play of Color in Gems?
Play of color occurs when gemstones appear to have color-changing properties. Broadly, play of color is an optical phenomenon that occurs due to specific characteristics in the stone. It could have to do with a gem's physical structure or the presence of inclusions, for example.
With many kinds of play of color, diffraction, interference, or both are responsible for the color-shifting phenomenon you see in certain gems. However, that doesn't mean each play of color type isn't unique, as they certainly do stand apart from each other.
Different Types of Play of Color in Gems
Adularescence happens with stones that have alternating layers of two different types of minerals. The layers cause the light that reaches the depths of the stone to scatter, giving the gem a glow that seems to sit below the stone's surface. That glow will also appear to float, shifting as the stone is moved.
When it comes to the look of the glow, it usually ranges from electric blue to milky white. Additionally, it tends to be more pool- or cloud-like.
Like many play of color gem phenomenon, it's easier to see adularescence when a stone is cut into a cabochon. The curve of the cut and the polish enhance the effect, making it highly viewable in gemstones that have this feature.
Adularescence is classically associated with moonstone, where layers of feldspar cause interference, creating a light phenomenon that gives the gem a shifting glow. However, it can also occur in other stones, including rose quartz.
While the color-changing aspect of asterism isn't as strong as you find in some other types of play of color, it is striking, nonetheless. When light hits the stone with asterism, it bounces off of fibrous inclusions, growth tubes, or needles in the gem. Once that happens, the light creates a star pattern, usually featuring four to six rays.
Typically, the star pattern is a lighter hue than the rest of the stone. In some cases, it may be a softer shade of the gem's main colors. In others, it may be bright white, helping it stand out more against the gemstone's base coloring.
Asterism can happen with a wide range of gems. Rubies and sapphires are the most popular gems that can produce asterism, but it also occurs in diopsides, emeralds, garnets, moonstones, spinels, and topazes.
While the stone type does play a role in whether asterism occurs, the cut also matters. It is typically only seen in cabochons, not faceted stones.
With aventurescence, you get a visual effect that gives the stone a metallic glitter that seems to occur deep within the stone. It happens with mineral platelets that have a particular orientation within the gemstone. When light hits those platelets – which are technically inclusions made of other minerals – they twinkle.
The mineral inclusion type can impact the color of the glitter effect. For example, when hematite is present, the twinkle may appear silvery. With copper or pyrite, it has a warmer, golden tone.
Chatoyancy is another word for the "cat's eye" or "tiger's eye" effect caused by fibrous inclusions within the gem. These thin, parallel inclusions are commonly referred to as "silk."
When chatoyancy occurs, you'll see a near-straight line across the stone that seems to move as you shift the gemstone. It mimics the shape of a cat's pupils when they become narrow slits.
There can also be a 3D illusion aspect to the phenomenon. With this, the stone seems to have more depth or could appear to glow.
Again, chatoyancy is a phenomenon that's easiest to see in cabochons, as that shape is best for displaying this form of play of color. It allows the band of light to shift across the stone's surface with ease, making it more noticeable.
If the chatoyancy seems to create two zones of color within the stone, with one side looking lighter than the other, that is called "milk and honey." The gem isn't actually two different shades; it just looks like way because of the optical effect.
A wide range of stones can exhibit chatoyancy, including actinolite, apatite, beryl, chrysoberyl, garnet, iolite, kyanite, moonstone, opal, peridot, quartz, spinel, topaz, tourmaline, zircon, and more.
Labradorescence is an optical effect associated with labradorite. It references the metallic shimmer you often see in the gem that creates iridescent blues, greens, reds, oranges, and yellows that appear to dance within the stone.
This play of color occurs because of interference between layers within the stone. Twinning surfaces cause the reflected light to enter different spectrums, creating the illusion of a wide range of hues.
When it comes to cut, cabochons are the most popular. However, care has to be taken to ensure it's cut in the right direction. The goal is to achieve full "face-up" color, where the labradorescense is strongest when the stone's face is viewed directly. If the wrong angle is chosen, the effect will either diminish or be unobservable.
You'll also see labradorescence in spectrolite. However, labradorite and spectrolite are essentially the same stone; they are just mined in different places.
As the name suggests, opalescence is the opal play of color variation of the color-changing phenomenon. With opals, the gem is made of layers of silica spheres. The spheres split the light into a full range of colors, creating a shifting platelet look with different segments taking on different hues.
In precious opals, the light produces a near rainbow of colors. You may see purples, pinks, blues, greens, yellows, oranges, and reds. Additionally, the strength of the coloring can vary from one opal to the next. Some will be incredibly vibrant, while others lean more toward pastels.
Fire opals have a more specific opalescence. In most cases, the dominant colors displayed are limited to flame-like hues, including reds, oranges, and yellows. However, it can still certainly have purples, blues, and greens; it's just that the warmer colors usually take center stage.
At times, the look of the color is due to the hue of the opal itself. Black opals typically exhibit very strong colors, while white opals- which can actually range from clear to soft gray – may have pastel or vibrant colorations in their opalescence.
It's important to note that not all opals have opalescence. Common opals may only have a milky sheen, giving it more of an adularescence look.
Read this article to learn more about gemstones that change colour under different lighting conditions.