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HCA very good spread

kindred

Brilliant_Rock
Premium
Joined
Dec 3, 2008
Messages
945
I posted earlier about two diamonds I was deciding between. I am pretty sure I am going to keep the GOG diamond, but I do have a question. The HCA score is Excellent for light return, fire and scintillation. But it is only very good for spread.

The numbers on GOG's website had some inaccuracies. Here are the numbers off the AGS cert:
54.4% crown
61.4% depth
33.7 degree crown
40.8 degree pavilion

A jewlery store told me the crown was a little small, and that that could make the diamond look a little smaller. I can't find the link now, but I think I remember Gary Halloway wrote that for good spread, a diamond should have a 56% crown, to... something I can't remember.

So I'm wondering if this diamond is what people refer to as "nearing steep/deep territory". I'm wondering if it is an excellent diamond, or only almost excellent, because of the spread. I'm also wondering why every diamond I've found through a search of pricescope's excellent cut diamond search scores only very good for spread. I mean, why are we paying a premium for a 1 ct. diamond if it's going to look a little smaller than that?
 

Stone-cold11

Super_Ideal_Rock
Joined
Sep 9, 2008
Messages
14,069
HCA is only a rejection tool, not a selection tool. Other tools, like idealscope, are progressively more restrictive rejection tool, no tool has yet been devise that is a selection tool.

That is table size, not crown. What your jeweler said is not necessary true, case by case, a large table with a large crown angle will make the overall spread smaller for a similar carat weight stone, simple geometry.

HCA will only give an Ex in spread if the depth is below 60.3%. Try it for yourself. This limit what kind of stone can get ex in spread as physical geometry will place a restriction on what is achievable without the girdle becoming too thin or non-existent.
 

kenny

Super_Ideal_Rock
Premium
Joined
Apr 30, 2005
Messages
29,148
61.4% depth is NOT near steep deep.

VERY few diamonds with HCA scores under 2.0 get an Excellent spread grade.
Most are Ex Ex Ex VG.
If I find an Ex Ex Ex Ex great, but I'd buy an Ex Ex Ex VG in a heartbeat if the IS images are good.

Diamonds that are well cut return so much light they look large for their weight anyway.

This diamond is HCA=1.0.
Since it scores under 2.0 the next step is to get an Idealscope image. https://www.pricescope.com/tools/ideal-scope

Compare it to this reference chart: http://www.ideal-scope.com/1.using_reference_chart.asp

zzz.png

009998.jpg
 

slg47

Ideal_Rock
Joined
Apr 4, 2010
Messages
9,667
HCA gives very good spread for many ideal cut diamonds. this one is not steep/deep by any means.
 

Liam-Spillane

Rough_Rock
Joined
Jul 17, 2011
Messages
21
Most idea cut diamonds won't have an excellent spread, only very good. As long as everything else checks out your fine.

Most diamonds with excellent spreads that are still nealy as pretty as ideal ones have slightly larger tables and slightly lower crown heights making them slightly shallower. All together a safe stone with good spread have depths around 58 - 60 and tables from 59-61. For the longest time until about the late 90s (internet take off) most people wanted 60/60 stones (table/depth) since the had better spread with a minimal reduction in fire and bueaty. I kind of agree with the old school, since women usually want the biggest size possible that is still very pretty and white.

I chose my stone over the true ideal ones because it had great spead and still looked great. Keep in mind the average ideal cut 3/4 carat stone measure 5.75-5.85 in diameter.

My stone:
GIA BR .75 VS2 G
Measurements- 5.97-5.99 X 3.52 (bigger spread)

table- 60%
depth- 58.8%
cut- EX (EX/EX)
crown angle 32.5 (slightly smaller than ideal)
pavilion angle 41
crown height- 12.5 (smaller than ideal)
pavilion height 43.5
no culet
thin-med girdle
 

kindred

Brilliant_Rock
Premium
Joined
Dec 3, 2008
Messages
945
What I meant to say was that the jewelry store told me that a small table can make a diamond look smaller, if you were comparing two diamonds with the same diameter. Is that true? What is the reason that so many diamonds that score well on the HCA have small tables?
 
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