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 » RockyTalky
»  » Star Facet Legnth/UpperGirdle Legnth and angle Dependent on one another
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Star Facet Legnth/UpperGirdle Legnth and angle Dependent on one another |
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| P: 9/6/2003 2:33:35 PM | |
Colored Gemstone Nut Ideal Rock Total Posts: 2,267 Last Post: 10/1/2009 Member Since: 11/21/2002 |
My questions come from Observing the working model GIA has published on it's website on the illustration of star facet length & how it affects a stones profile face up and how the other facets change and vary in size and angle based on that length. I am wondering is the Facet length and angle of a star facet & upper girdle facet dependent on one another. It would seem if a cutter cuts the upper girdles at a steeper angle it would affectively in turn shorten the star facet length where it extends out to the outer most tip at the junction where the 2 facets meet and cutting longer star facets would decrease the upper girdle angle. Am I right in my assumption that with set crown & pavilion angles and a given table, that the kite, star, & upper girdle facets are all connected and a subtle change in the angle a star facet or upper girdle facet is cut will affectively change the other facets which are connected and dependent on the way the connecting or adjoining facets will look including facet angle/height/width variation but will not affect any other aspect of the stone like the table, crown angle or pavilion angles? -Josh Rioux Sitka, Alaska  Josh Rioux Haines, Alaska *The Colored Gemstone Nut* |
| Posted: 9/6/2003 2:33:35 PM | |
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There are 1 replies to this message. There are 1 replies on this page. |
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| P: 9/6/2003 5:02:11 PM | |
Garry H (Cut Nut) Ideal Rock Total Posts: 11,579 Last Post: 11/23/2009 Member Since: 8/16/2000 |
The crown angle is set by the bezel (kite) facet. The star that joins the table, and the 2 upper girdle facets that join it are connected such that if the upper girdle get steeper then SO TO DOES star facet. Upper girdles may rise from say 40 degree to 45 degree and leak more light / increase fire, but they get smaller as part of the overall surface area, so have less impact. As they both get steeper, the star may rise from say 20 degrees to 24 degrees, which has little or no impact on the light returned to a face up observer per square mm of the star facet --- but the star facet gets much bigger, so light that may be lost from the steeper upper girdles is mostly made up for by the larger star facets. End result is there is very little impact on a diamonds beauty. The best way to understand this is to use DiamCalc - even the free marquise program would help 
Garry Holloway FGAA DipDT |
| Posted: 9/6/2003 5:02:11 PM | |
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