These special effects, called "phenomena" by gemologists, are part of the very nature of the material and are caused by the effects of light itself within the piece. Skillful lapidaries use sophisticated cutting and polishing techniques to enhance these optical effects in gemstones, while organic jewelry-making materials can require light oiling to maintain their effects.
Here's a list of the most common gemstone special effects, including a brief explanation of what each effect is, how it looks to the human eye and what jewelry-making materials it is likely to appear in.
Chatoyancy (sha-TOY-en-see) comes from the French phrase for "eye of the cat," and jewelry makers will frequently see this effect in materials named after felines: cat's eye quartz, tigereye and others.
The shimmering effect comes from light reflecting from fiber-like structures within the stone. This reflection appears to "move" as the stone is moved, creating the illusion of an eye in the stone. Gemstones displaying a high level of chatoyancy are usually carved in smooth shapes (such as rounds, ovals or as cabochons), as faceting decreases the strength of the effect.
Asterism is derived from the Greek word for "star" and is a form of chatoyancy which specifically exhibits a luminous six-pointed star when cut into a cabochon or other round shape.
This "star" is created by the presence of dense inclusions of tiny rutile fibers (the same kind that are dark in rutilated quartz). This is commonly referred to as "silk" by gemologists and lapidaries. The rutiles are aligned perpendicular to the rays of the star displayed on the surface and create a range of opacity in any stone in which they are present.
Iridescence (eer-ih-DESS-ens), from the Greek word for "rainbow," is an optical effect where colors on the surface of an item appear to change with the angle from which it's viewed.
Iridescence creates the colors floating on the surface of oil slicks in a parking lot, or soap bubbles in the sunlight. It comes from multiple reflections within two or more transparent or semi-transparent layers. Light enters the top layer and "bounces" around between the layers. Iridescence can include a variety of rainbow effects in gemstones, including schiller (SHIL-er) and labradorescence (lab-rah-dor-ESS-ens).
|Opalescence (o-pul-ESS-ens) is named after the gemstone which displays its properties the best: the opal. It refers to a particular pattern in the play of colors within a stone. Similar to iridescence, opalescence is created by the reflection of light within the stone material, and its dispersion out of alignment with its entry. Opals are created of multiple spheres of silica, which trap light as a raindrop does, "bouncing" around inside and exiting to create a rainbow.|
|We would like to share some of the customer comments we received in response to the article "Special Effects in Jewelry-Making Materials," as featured in an email newsletter. Please keep in mind that the comments expressed below are those of our customers and do not reflect the views of Fire Mountain Gems and Beads.|
"I love it because its stones I love!"
"Enjoyed the article on gemstone special effects. Wish I still had my old geology text. Thanks especially for the definition of chatoyancy; I can point to it, but defining it for someone else is harder. Keep it up!"
"Thank you so much! I love your products and the way you conduct a "personalized" business."
"This is a very interesting overview of stones with "light-play?" in them! What do you call stones like seraphinite and rutilated quartz?"
"I love the "Special Effects in Jewelry-Making Materials." It was full of information that I was not aware of. I hope it will be part of the newsletter each month."
"I like the article, except you mention they may require light oiling, but don't mention the type of oil to use. Thanks,"
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