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Grading Colored Gemstones Carl Wozniak. Grading colored gemstones  Color stone grading is considerably different from diamond grading  While the “4

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  • Grading Colored GemstonesCarl Wozniak

  • Grading colored gemstonesColor stone grading is considerably different from diamond gradingWhile the 4 Cs of diamond grading still applyColorCutCarat weightClarityBy far the most important is Color

  • Grading a colored gemstoneSome stones just seem better than others. Lets see why.Three main factors merge to create the best colored stones:Good colorGood shape appealGood light returnWe can quickly estimate these to find the best stones

  • Which would you buy?$2,100.00$45.00

  • Stone shapes

  • Stone styleStones can beRoughTumbledFacetedCabochonBeadSphere

  • Color Color is the most important component of value in colored stonesUse modifiers to note the tone and saturation of the stoneThen note the hue of the stone. Stones rarely are pure colors

  • Color-toneTone is the relative lightness or darkness of a hueExtremely lightVery lightLightMedium lightMediumMedium darkDarkVery darkExtremely darkBlack

  • Color-saturationSaturation is the strength or purity of a hueGrayish (brownish)Slightly grayishVery slightly grayishModerately strongStrongVivid

  • Color-hueHue is the shade, tint or sensation of a colorMost stones arent purely one color, but modified shades of two colorsOrangish-redReddish-purple

  • Describe the color of this stoneMedium dark, moderately strong, purplish-red

  • Light PropertiesThe light properties of the stone are next in importance in determining value. We judge the quality based on three factorsWindowingLight returnExtinction

  • WindowingWindows are areas of stone transparencyThey are visible as light areas on the face of the stone through which you can see objects beyond

  • WindowingWave an object, like a pen or pencil, underneath the stone while looking through it and estimate the overall surface percentage that shows motion in it

  • Light return and extinctionLight return is shown by bright areas on the stones surfaceTilt the stone up to 30 in each direction and estimate the percentage of the surface that is lightGood stones = +45% light return

  • Light return and extinctionThe dark areas represent light that is lost from the crown of the stone. You estimate its percentage also.

  • Light return and absorptionWhat are the window, light, and extinction percentages of this stone?Window: about 0-5% Light: about 45-55%Dark: about 45-50%

  • Light return and absorptionBe careful with reflections on facets. You need to look through the reflection to see the internal light and dark areas.

  • What are the light properties of this stone?Window: 10%Light return: 35%Extinction: 55%

  • Lets completely grade a stoneStone IDRhodolite garnetStone shapePear, broad wingsStone styleFacetedColorMedium, moderately strong, purplish red

  • Lets completely grade a stoneLight propertiesWindowing10%

  • Lets completely grade a stoneLight propertiesWindowing10%Light return45%Extinction45%

  • Lets completely grade a stoneOverall stone quality:


  • How about this one?

  • Now lets do it with real stones...

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