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Depth and Table

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discostu

Rough_Rock
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Nov 18, 2005
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Are there any issues with the table and depth being the same? It seems the brilliance of the diamond would be affected. Is this necessarily true?
 

belle

Super_Ideal_Rock
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Nov 19, 2004
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10,285
this link may help answer your question
2.gif
 

oldminer

Ideal_Rock
Trade
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Sep 3, 2000
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The link provided is an excellent one. There are some diamonds with equal table and depth that look very good and others that just don''t look so good. So many variables can change while still retaining table and depth numbers that are equal. The diamond business is slowly drawing away from numbers and parameters as being the best or only way to judge the beauty of a diamond. Even when we measure a whole bunch of physical attributes of the cut of a particular diamond, we don''t measure enough of the many we could measure to truly and accurately judge the beauty It may be a pretty decent, approximate assessment, but probably not a perfect one.

Diamonds are sold by incremental, generally invisible, classifications of their quality. We want to encourage the best information possible to get to consumers. Measurements of physical features are quite helpful. I developed early versions of this back in the 80''s and still use them today, but newer and better measures are just beginning to appear. Of course, some methods will be superior to others, but all of this is rather new to the rather traditional diamond business.
 

AndyRosse

Ideal_Rock
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There are also some threads here on PS about 60-60 stones:

LINK
 

beryl

Shiny_Rock
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Nov 6, 2003
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288
With 60% table, 60% total depth is an ideal match, within the reasonable limits indicated in the link (39°-42° pavilion main slope). For other table sizes, other depths are best which are not equal to the table size.
I wrote on this in ''DiamondTalk'' circa 2001 and will dig-out the reference data if there is sufficient interest.
 

discostu

Rough_Rock
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Nov 18, 2005
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Thanks everyone for the information and the links. Beryl, I would love to read that information. The issue is the table is 59 and the depth is 59. I don''t have crown or pavilion angles.
 

beryl

Shiny_Rock
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Nov 6, 2003
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discostu:
I guess the difference between 59% table/59% pavilion and 60% table/60% pavilion is insignificant.
If time permits, I will try to find the reference material I did previously.
 

beryl

Shiny_Rock
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Nov 6, 2003
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Here is chart for 60% table from 2001 Aug 04, including results of light return tests by MSU and GIA at that time.
The blue daigonals give the total depth without girdle or culet; for a typical diamond we subtract nothing for no culet and add 2.7% (~3%*) for thickest points of girdle (see last week's article on 'Scallops'). Thus a diamond with pavilion main slope of 40.5° and crown main slope of 34.5° has a total depth of 56.7% + 2.7% = 59.4%, or ~57% + ~3% = ~60%.
The red lines show what MSU and GIA test data indicated as 'best'**; note how similar they are. These go from ~56% to ~57% total depth without girdle, = ~59% to ~60% real total depth. This verifies the 'myth' that any stone with 60/60 is good - but shows the limits cited in the link cited by Belle. In this example, MSU had run their tests with 60% table, and the blue curves are calculated for 60° table. GIA had used 59% instead of 60%, so the plot is not exactly correct for them - but close enough. Note that according to GIA your 59/59 stone is about as good as a 60/60. This is not true for other tables.

* '~' means 'approximately'. It is silly to be too accurate in cases like this.
** my interpretation of 'best' from MSU and GIA test plots. MSU data for their 'Q-factor', which combined brightness and 'fire'; GIA data for 'weighted light return'.

totaldepth60x.GIF
 

beryl

Shiny_Rock
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Nov 6, 2003
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The chart attached here is for 56% table, for which GIA ran tests. The 'best' line (red) runs right along the 58% total depth line + 3% girdle = 61% real total depth. So, in this case, 'best' table/depth proportions are 56/61 = not the same and diverging (one gets smaller as the other gets larger) - a 3% decrease in table size is accompanied by a 1% increase in depth for 'best' results.

totaldepth56x.GIF
 

beryl

Shiny_Rock
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Nov 6, 2003
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This chart is for 53% table, which both MSU and GIA simulated in their tests; note, that the ''best'' depths according to their data differ by from 0.5% to 1.0% = not significant.
GIA ''best'' go from 62-63% with 3% girdle, whereas MSU go from 61-62.5% with the same girdle. We can approximate this by saying that for 53% table, 62% total depth (including girdle) is best - or table/depth combination of 53/62 - = again a 1% incease in total depth for 3% decrease in table size.
The red ''T'' is per GIA for Tolkowsky because he cited 53% table. But he made a calculation error; it should have been 54%. Jasper Paulsen also notes this error. Its not important now - we have learned that there is no one best set of proportions and that the proportions preferred by some are not preferred by others.

In summary: 60/60 or 59/59 are perhaps the only ''best'' combinations where the two numbers are equal. Note that various combinatons of pavilion and crown main slopes can give these same combinations.

Forget the numbers - look at the stone. If you like it, buy it.

totaldepth53x.GIF
 
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