[Crw-talk] Chatoyancy

[John & Donna Griffiths]

Thanks Duane

Today I have been working on a cottonwood bowl and I find it has 
marvelous chatoyancy around a knot.

John
On 12/17/2012 2:58 PM, wisawdust at charter.net wrote:
> I was asked at the meeting (by our president) to spell and define 
> chatoyancy.
>
> ChatoyancyFrom Wikipedia, the free encyclopediaJump to: navigation, 
> search Cat's eye effect redirects here. For other senses, see Cat's eye.
> Tiger eye
> Tiger's eyeIn gemology, chatoyancy ( /???t??.?nsi/ sh?-TOY-?n-see), or 
> chatoyance or cat's eye effect,[1] is an optical reflectance effect 
> seen in certain gemstones. Coined from the French "oeil de chat," 
> meaning "cat's eye," chatoyancy arises either from the fibrous 
> structure of a material, as in tiger eye quartz, or from fibrous 
> inclusions or cavities within the stone, as in cat's eye 
> chrysoberyl.[2][3] Marder and Mitchell demonstrated that the 
> precipitates that cause chatoyance in chrysoberyl are rutile, titanium 
> dioxide. There was no evidence of tubes or fibers in the samples 
> examined. The rutile precipitates were all aligned perpendicularly 
> with respect to cat's eye effect. It is reasoned that the lattice 
> parameter of the rutile matches only one of the three orthorhombic 
> crystal axes of the chrysoberyl, resulting in preferred alignment 
> along that direction. The effect can be likened to the sheen off a 
> spool of silk: The luminous streak of reflected light is always 
> perpendicular to the direction of the fibres. For a gemstone to show 
> this effect best it must be cut en cabochon, with the fibers or 
> fibrous structures parallel to the base of the finished stone. Faceted 
> stones are less likely to show the effect well.
>
> Gem species known for this phenomenon include the aforementioned 
> quartz, chrysoberyl, beryl (especially var. aquamarine), tourmaline, 
> apatite, moonstone and scapolite. Glass optical cable can also display 
> chatoyancy if properly cut, and has become a popular decorative 
> material in a variety of vivid colors.
>
> The term Cat's Eye, when used by itself as the name of a gemstone, can 
> only be used to refer to a Cat's Eye Chrysoberyl. Any other stone 
> exhibiting this phenomenon must have the stone's name after the Cat's 
> Eye identifier, e.g., Cat's Eye Aquamarine.
>
> Chatoyancy can also be used to refer to a similar effect in 
> woodworking, where certain finishes will cause the wood grain to 
> achieve a striking three-dimensional appearance; this can also be 
> called pop-the-grain, wood iridescence, moire, vibrancy, shimmer or 
> glow.[4] This effect is often highly sought after, and is sometimes 
> referred to as "wet look", since wetting wood with water often 
> displays the chatoyancy, albeit only until the wood dries. Oil 
> finishes and shellac can bring out the effect strongly.
>
> Duane
>
>
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