Grading colored Stones
Any gem whether it be a Diamond or Colored Stone is graded by the 4 c`s That’s Color, Carat, Cut and Clarity. These factors determine the rarity of each stone and ultimately the value.
No two people will value a gemstone equally , each individual is different and each person’s likes and dislikes are different, hence here we try to understand what factors each person looks for in a gemstone to arrive at a monetary value.
In colored Gemstones color is a primary factor, the main questions we ask are
Is it pleasing to the eye ?
Are there secondary colors visible ?
Any grayish areas on the stone ?
Is the color evenly spread ?
If it’s a star or eye is it strong , sharp and work around the stone ?
The more vivid the color and purer the color the more value we place on the gemstone.
Carat is the measurement of weight we use on colored gemstones. 1 carat is equal to 200mg . Larger the stone rarer it is. And price increases exponentially , a 0.5 carat Blue sapphire might be say US $ 400 per ct , but a 1 ct stone will be US $ 1000 per carat.
Gems are basically divided into three categories by the GIA for purposes of clarity grading. Type I, type II and type III. I will quote from the GIA Colored Stone Grading Workbook.
Type I Colored Stones (Often virtually inclusion-free).
Type II Colored Stones (Usually Included).
Type III Colored Stones (Almost always included).
Example: Emeralds, Hessonite garnets
As you can see, a type I colored stone VVS grade is eye clean with inclusions that are difficult to see under 10x magnification and invisible to the unaided eye, while a type III VVS has inclusions that are easy to see under 10x magnification and may have eye visible inclusions. Sapphires normally do have natural feathers which can be seen at 10 X magnification but is hard to see with the unaided eye.
The Accuracy of the Facet meeting, polishing marks on the surface, Overall Proportions used for internal light reflection, Culet Angel used are some of the factors that determines the value of the Gemstone.
Sapphires are mostly still today are cut to retain weight , the cutter tries to work around the natural formation of the stone to get the maximum weight retention.
A badly cut stone with a window may have a lot of weight but since its not faceted properly it will not be attractive.
Precision cuts are now in the market, these are Stones cut by master cutters and gemstones are more symmetrical and well proportioned. These give out better light performance and brilliance and since more of the stone has been wasted to get this perfection the stones usually cost more.
“Beauty is in the eye of the beholder “
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