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Grade 5 - Example 1 - RD39
Table: 57%
Crown >: 35.5°
Pav >: 41.2°
Stars: 55%
lower girds: 80%
girdle: ex. thick
culet: none
depth: 74%
polish: G
symmetry: G |
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| This diamond's grade is limited by its weight ratio. the somewhat steep crown angle, slightly steep pavilion angle, and very thick girdle greatly increase the total depth. Therefore, this diamond's diameter is much smaller than its carat weight would indicate. |
Click on the graphic to download the .gem file |
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Rhino's Review
What's interesting about this first example is that GIA has chosen to use angles & percentages which for the most part are representative of the current AGS Ideal "0" grading standards with the obvious exception of total depth (74%!) caused by an extremely thick girdle (and also the fact that it didn't get the highest marks for polish & symmetry). The HCA would not grade a stone with a 74% depth so I reduced this to 65% to get a score which in this case accurately weeds out with a score over 2. All the whites you see under the table in the LightScope image are indicative of leakage and are a demonstrative example of the weakness of AGS' current grading system (ie. a proportion based system as opposed to a performance based system). Excessive leakage within diamonds such as you see in this example are the causes for facets appearing darker than they should and this even is less desirable when it happens under the table. Here is an optical analysis on a diamond we have scanned in that very closely resembles this one with the exception of its depth (ours is more shallow with a proper depth, however the angles are comparable to this example). 1.23ct F VS2 H&AOur Sarin measured this diamond with angles of 35.5/41.2 (just like this GIA example). I can understand this stone getting a Grade 5 classification primarily because of its depth (which GIA notes) but this set of angles are less steep/deep than Grade 2 - Example 2 in this tutorial which would lead me to believe that if the depth of this stone had been more in the mid 60% range would get a Grade 2 classification instead of a miserable Grade 5.
Grade 5 - Example 2 - RD43
Table: 57%
Crown >: 38.5°
Pav >: 41.8°
Stars: 55%
Lower girds: 80%
girdle: thick-very thick
culet: none
depth: 71.5%
polish: G
symmetry: G |
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| This diamond's grade is also limited by its weight ratio. the somewhat steep crown angle, slightly steep pavilion angle, and very thick girdle greatly increase the total depth. Therefore, this diamond's diameter is much smaller than its carat weight would indicate. |
Click on the graphic to download the .gem file |
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Rhino's Review
Another excellent example of a poor set of angles. GIA makes note of the depth (as in the first Grade 5 example) however add to this the excessive leakage caused by this set of angles and that alone would be enough to make it a pooper. :) These first 2 examples are also obvious candidates for rejects by observing red reflector images which show excessive, obvious leakage. As we collect more examples of actual diamonds we've scanned in we'll be including links to those as we scan them in.
Grade 5 - Example 3 - RD45
Table: 62%
Crown >: 37
Pav >: 45.2
Stars: 60%
Lower girds: 85%
girdle: med-v.thick
culet: none
depth: 69.3%
polish: G
symmetry: G |
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| This diamond's grade is limited by its fire and scintillation. The slightly steep crown angle, very steep pavilion angle, and large total depth all cause this diamond to have a very dark table area, along with a very dark upper-girdle areas. |
Click on the graphic to download the .gem file |
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Rhino's Review
Of all the diamonds in these examples this is by far the worst. :) An extreme example of what we term in the industry as a "nail head" caused by all the darkness observed under the table which is the result of way too much head obstruction (blockage of light) to the point where virtually no lights are observed under the table providing for lousy contrast. Excessive leakage on the upper girdles is what causes the darkness GIA makes note of and can easily be observed in the 1st graphic as well.
Final thoughts on Grade 5
Each of the examples given for this grade classification also have obvious red flags even to the most rudimentary arm chair gemologist. Total depths in the high 60's to mid 70's is enough to know something isn't right. The rest of the data just confirms. Grade 5 really sucks! :) Right on GIA! To my surprise they did use an example of angles not as steep/deep as I would have thought with the first example. I would have thought that would have been used as a good example for a Grade 2, however the 74% depth was the qualifying factor for the Grade 5. It'd be interesting to see what Grade that would have got if the depth were more in the mid to low 60's. The last 2 examples are kind of what I expected to find in a Grade 5. |
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