Can Crown & Pavilion impact depth percentage?

[Defender]

Here is another questions that may come off as naive, but I am still a newbie. Maybe I am probably trying too hard to understand some of these dimensional issues

How much can the crown height and angle impact the depth stats on a fancy cut such as an emerald. For example can a deepish stone with a nice % in the crown look better than the basic GIA depth and table statswill show?

Will a Sarin or AGS report with more information help to deciper where a deeper stone still might have promise in a fancy cut such as an Emerald. For example, can a stone with low 70% depth and a 40% crown angle look better than a deep stone with a smaller crown angle and height??

IF this is another stupid question you can ignore me.

Thanks for your patience

 

[valeria101]

Gotta problem with these numbers for emerald cuts...

For once, there are three crown angles and three pavilion angles (each for every step). Sarin cannot read them well...and this is a badly kept secret... that Sarin works better on rounds than fancies and even then.

The bad news is that even if hard to measures, these angles determine what the diamond ends up looking.

Crown height and pavilion depth give a rather rough approximation of what these angles are, and while I would think these approximations could be qualified (good, bad, ugly or uncertain), I have not taken the time and have not found any such study done. Except.... have you seen those AGA charts under ''Knowledge'' / ''Fancy Shapes'' on top of these page? They don''t claim to guess brilliance based on proportions, but I would guess that... there is some relation. Probably not precise enough to allow a bold claim from a responsible appraisal business. But I would rather expect higher brilliance from those stones rated in the first 2-3 grades by those charts than below that. Not that I would bank on that so to speak - there should be some reason why AGA doesn''t claim to guess brilliance based on such scarce stats (table, crown, depth, girdle... finish, ''guess that''s what they use).

So what to do?

#1. you could ditch the concerns with Sarin and numbers, take a pic from the range of the top three AGA tables and ... look at it. There is a nice reference chart on www.ideal-scope.com showing some hunts of what to look for in an emerald cut. I couldn''t agree more with those guys

#2. you could take up the task of making your own study of emerald cut proportions, and use that to read through Sarin''s measurement error. Not a weekend job, I reckon... It looks like AGS is doing just that for square emerald cuts (see Wink Jones''s report from their latest conclave - there is a thread with it, ''couple of weeks old). They take it seriously, and while I am inclined to believe that the high tech approach is a wee bit over the top, this is what it has come to and I reckon'' that their impressive research effort is a good gauge of the task.


For me this is a hobby - I am not expert... The step cut is my favorite of the classic cuts (otherwise tend to favor odd fancies).

Hope some of this makes sense.


Do you have a specific stone in mind? It may be easier taking just one example rather than making up theory.

 

[valeria101]

I had a bit of trouble understanding the question: sure crown and pavilion angels determine total depth... because total depth = crown height + pavilion depth + girdle width (on the short crossection), and adding in table size, those angles determine crown and pavilion heights... Sure you didn't ask that.


It sounds like the questions is: 'would a deep emerald cut diamond look better with a higher crown than a low one". That's pretty interesting. And I am afraid I don't have an answer (the previous post applies).


Just one note: 40% crown does not happen. They are usually around 10 (more likely below than above), and definitely below 20% on modern cut diamonds.

40% is quite a mountain!

Btw. these % are not of the total depth, but of the diamonds width. (so total depth 70%, crown 40% leaves the pavilion depth below 30% - which is not a likely configuration at all).


This is about all that comes to mind quickly.

 

[strmrdr]

with EC seeing it in person and or pictures talk and numbers walk.
The crown height is important but other than that....

 

[Defender]

OK, Here is one stone I found that might fit this question is an emerald.

3.04 carats...
67% table
73 depth (i know this is very deep and makes it look smaller dimensionally)
14.4 %crown
40 degree crown
56.9 pavillion %
44.8 degrees pav. angle

this is an AGS certed stone with noted "excellent" symmety and "excellent" polish.

So, is this worth calling in to look at? or does it sound like a loser?

 

[strmrdr]

whats the height and width?

 

[Defender]

9.14 x 6.99 x5.11

 

[strmrdr]

I can say that some of the best looking EC that Iv seen where in that depth range.

for example these 2:
http://www.goodoldgold.com/emerald_0_96ct_f_vs2.htm

http://www.goodoldgold.com/emerald_1_01ct_d_vs1.htm

 

[strmrdr]

overall yea I think its worth bringing in for pictures.
There isnt enough info to make a dc model but entering the info provided shows it could work well if it was cut right.

 

[Defender]

The other issue is that this is a J color by AGS. For my budget, I have been stuck in this color range, but this AGS stone with excellent polish and symmetry is selling at prices comparable to EGL prices. That is what garnered my attention and questions.

I found it unsuall to find an Emerald in virtual inventory with an AGS certificate at a very agreeable price. The price seems based on J color and a depth that puts it out of normal ideals for cut quality. I was just wondering if this could be a "sleeper"

 

[strmrdr]

hard to say
how much they want to bring it in?

 

[Defender]

Here is crop from cert:

The price is $5586 per carat or 16,980

 

[valeria101]

Date: 3/11/2006 1:06:20 PM
Author: Defender
9.14 x 6.99 x5.11

If this size is ok, you could be looking for 2.5 cts easily.

It may be easier to guess how good or bad the spread is by looking at the dimensions of diamonds of the same cut (or any other you might consider as an alternative), within a range of half carat or so.

E.g.

2.5cts I/VS2 (GIA) LINK slightly larger 9.3 x 7mm & 16k


I would look for SI1, despite the often heard rumor that eye clean SI step cuts are only getting out of their hiding with the blue moon.

There are more than that and chances are you will get to see one if you ask for them.


I would be happy to play with numbers all day long, but never knew what Sarin measures as angles for step cuts: the first steps near the girdle, the average or some intractable medley of all 12 angles there.

Given that the dimensions given do not add up with the angles, I gave up on this one.

Btw. there is usually a premium on the finish grades (mostly for the top ones only), but these have little to show for themselves. Even about cut - proportions and brilliance is vastly more visible. I would not care much if they are 'Good' or 'Excellent'. If these turn out 'Excellent' for a diamond that already has good brilliance, acceptable grade and spread... fine, otherwise no.

Just my personal take on things, of course.

 

[valeria101]

Sorry if it sounds like I am pestering you... Sarin reports with similar numbers for step cuts diamonds come up quite often, and I have every intention to refer to the same scheme. Besides, it took 5 minutes flat to sketch

 

[Defender]

Thanks Valeria.I did not mean to make you do so much work!

I understand the basic premise, and come to the conclusion that I picked out this stone due to the readily available AGS info.---which is not really as exacting as it appears.

I also see that while the price is good for a 3.00+ stone, this is really not valid since the 2.5 stone that you compared has larger visible dimensions. The stone that I inquired about might be more worthy if it was priced in the same range as a 2.5 stone with similar color and clarity...but it isn''t.

Thanks for helping my diamond education