Suggestions on Princess with Low Crown Height?

[mark44]

Hi everyone,

I''m considering a Princess cut stone at goodoldgold.com and wanted some opinions on the specs. The LightScope and BrillianceScope look pretty good, but not sure about some of the Sarin info (crown height is only 7.6%). Is this a concern if the light performance is decent?

Specs are as follows:
Stone: http://www.goodoldgold.com/0_74ct_evvs2_princess.htm
5.02 x 5.11
Depth: 69.3%
Table: 67%
Crown: 7.6%

The small crown height puts it at 2B on the AGA cut grading chart.

Any opinions/suggestions are much appreciated!!

mark

 

[mark44]

Bump ...

Any comments on this stone?

Thanks,
Mark

 

[belle]

it appears that the stone you are looking at would benefit from a higher crown...
here it is with the 7.6 crown

 

[belle]

here is the same proportions with a 12.6% crown....

 

[Allium]

Not a great looking stone. There''s quite a bit of leakage there. I would keep looking. There are lots of better ones out there but you need to be patient.

 

[valeria101]

There are IS and BrillianceScope tests, and GemAdviser charts for that stone showing... a beauty! What counts is the way that crown height works together with the rest of the details of the cut.

Princess cuts are allot more difficult to model than rounds because one needs allot of extra numbers about the pavilion facets and the relevant angles for either side of the stone (they may not be the same on both sides of a corner...). I cannot know if the model cited by Belle took that into account, but the presentation at Good Old Gold done with the stone at hand has. And the results look great.

Now, princess cuts usually come with lower tables - some may like that, others (like me) less so. That does notmean that low tables do not have their admirers and benefits.

There are soem princess cuts made with higher crowns: try Exceldiamonds for their brand and Wink for their AGS0 princess cuts. About the AGS0 princesses there are some useful threads too. However, the high crown also means extra depth in these (towards 80% and sometimes over). The AGS and Excel branded cuts may have consistent light return and a special look (perhaps unlike the usual princess cut even - the proportions are not common at all) - but they also have smaller diameters due to the deep cut. And the expected brand''s premium, of course. On average, generic princess cuts are prices less per carat than rounds to account for their lesser size relative to rounds - the branded ones are not, so they are very bright, small, expensive stones

Love them or hate them...

Of course, there''s always the exception to the rule: a brilliant princess cut with great spread (size for weight and price), top light return and a high crown if you wish. But that''s bound to be a rare animal.

 

[Garry H (Cut Nut)]

Belle you need to be careful modelling Princess in diamCalc.

The variations in chevron facets as outlined in Beryl''s current topic will lead to many errors.
I too think this stone has a lot of leakage, but do you know how to import Rhino''s GemAdviser 3D scanned model into DiamCalc?

As you can see the values from the actual scan are a lot better than your estimate.

I would be more concerned that the stone probably has a crown angle below 30 degrees and could chip easily. (but i have not checked - and you can do this with diamcalc too - do you know how?

 

[moremoremore]

Looks quite pretty in the picture though. Tough call.
how about a nice 1.0 F Vs2? Hehehehe.

Hmm, never mind. That's a good price!

 

[Garry H (Cut Nut)]

This link (first post at top of page 2) https://www.pricescope.com/community/threads/user-tips-for-diamcalc.32366/page-2 explains how to open Gem Adviser files in DiamCalc.

MoreMoreMore, I have seen very few photo''s that accurately display a diamonds appearance. That one is not one of the most accurate.

 

[strmrdr]

The b-scope isnt the end all of diamond cut grading but here is what its telling me.
The diamond is cut for good light return and the lightscope photo agrees with this.
The colored light return also known as fire takes a hit from the low crown but is still not too bad.

Looking at the b-scope photos confirms this mostly white light and not a lot of blues and yellows.

 

[strmrdr]

Here is one that is cut the oposite performance wise.
http://www.goodoldgold.com/0_91ct_g_vs2_princess.htm

lower white light return and higher fire return.

Very high crown accounts for a lot of that.

 

[Garry H (Cut Nut)]

At this link (and many others) there is a description of thin film Interference colors http://home3.netcarrier.com/~chan/EM/PROGRAMS/THINFILM/

This stone seems to exhibit this effect.
It is one of the reasons that I do not like the BScope

 

[strmrdr]

Date: 8/21/2005 3:59:01 AM
Author: Garry H (Cut Nut)
At this link (and many others) there is a description of thin film Interference colors http://home3.netcarrier.com/~chan/EM/PROGRAMS/THINFILM/


This stone seems to exhibit this effect.

It is one of the reasons that I do not like the BScope

I need to look into it more when im awake but unless that diamond is dirty i just dont see it happening.

Iv looked at hundreds if not thousands of b-scope photos and I dont see anything unusual about those.

Then again I couldnt care less about princess cut diamonds anyway so its mostly rounds and asschers iv looked at.

 

[strmrdr]

Also as im sure you know the center picture is a composite of several pictures and iv seen some wierd things on the center picture from time to time and totaly ignore them.
So that might be what your seeing too.

 

[Garry H (Cut Nut)]

The effect is most obvious in the top left 2 images Storm.
It is a result of some air between the table and the glass plate.
ISee2 and Imagem can also have this problem. We noticed it on ideal-scope photos when we experimented with table down photographic systems.

You can see that the colors are lower order than spectral colors, and they are confined to the table where the tiny bit of trapped air causes the optical interference.

It is the same thing you see when there is oil on a pavement at a garage.

 

[strmrdr]

Can you draw a circle around where your talking about on the images?

 

[strmrdr]

I looked at the image at up to 10x and im still not seeing anything wierd there is the normal gif encoding blockyness and the color compression you get with gif files but im not seeing it.
Will try again after some zzzzzzzzzzzzzzzsssssssssssssssssss.

 

[Garry H (Cut Nut)]

Sweet Dreams Storm.

When you wake up, see this image with colors that are not the same as dispersion colors - they are more muted.

This color is not going to be visible unless you wear the diamond with a bit of glass stuck over the table.

This is part of the explanation on the link i posted above:

Whenever a thin transparent film of one material is over another, interference colors will be visible. A common example is a thin layer of oil or gasoline on a puddle of water after a thunderstorm. The interference colors also appear when a flat piece of glass is laid on top of another (known in this case as Newton''s fringes). Here, the "film" is the small air gap between the two pieces of glass.

The origin of the colors is interference of light. Light is partially reflected from the top interface (between the film and the ambient which is usually air) and from the lower interface (between the film and the material that the film is on). As the light of a particular wavelength passes through the film, its phase changes by an amount proportional to path length through the film and inversely proportional to the wavelength. The path length depends on the film thickness D and on the angle from normal that the ray propagates through the film.

 

[Serg]

Garry,

Well done

Very good example about problems with direct measurement systems.

But I think Imagem does not measure Fire at all.

 

[pricescope]

Nice catch, Garry. Now one have to find out how much this affects the colored light readings.

We need an example with interference and low fire (colored light reading).

Also one can try to measure the same stone trying to get rid of the interference film and compare the fire readings.


Here is a round stone with interference colors in BS

 

[strmrdr]

DUH
Got it now.
I was looking for something different from normal in those photos and it was something perfectly normal for BS photos you were talking about.

With it being a known problem i dont see why it couldnt be accounted for.
Trying to perfectly level the stone would be a much more error prone way of doing it.
It seems to me while not perfect its a trade off that had to be made.
AGS went the same way with the desktop ASET.

 

[Garry H (Cut Nut)]

Introducing low order colors into the ASET image would have little effect.

BScope is counting those pixels of color and reporting them in fire results

 

[belle]

very interesting re: the bscope results...as i start looking, it seems there are many images that posess this phenomenon.

garry,
is this what you were asking me to do regarding checking the crown angle?

 

[Garry H (Cut Nut)]

Belle you have mastered DiamCalc

 

[RockDoc]

RE: Interference Colors in B Scope Scan


We have deternined many times that this is could possibly be a result of static electricity. It could also be oil on the stone, or the chemical that is in compressed air.

What is sort of unusual to me is that the colors seem to be limited to the table area. When I''ve seen results like this they are generally not limited to one area of the stone so distinctly.

We have some corrective measures when this happens, and usually that cures the "problem".

Rockdoc

 

[Garry H (Cut Nut)]

Thanks Roc,

The problem is associated with very thin areas of contact, so it can only occur at the table / air interface.

 

[belle]

regarding bs results and interference colors:
would it be possible to try and achieve higher color light return results on a stone by using a thin layer of oil or compressed air?

 

[mark44]

Hi everyone, lots of activity now on my question! (bit over my head ...). I''m considering the stone I mentioned at Goodoldgold.com, as well as a Superbcert from Exceldiamonds.com. Interesting about the effects of the low crown. I''ll post again if/when I make a decision!

 

[Rhino]

A couple of comments.

1. Generally when we see diamonds with this crown height we avoid calling them in. Admitedly, chances of finding a hottie with that crown height is not probable. The factory sent the stone to us for examination because they did feel it had great optics so we had them send it for confirmation. This stone is one of those rare cases that breaks the rules.

2. In princess cuts, Gem Advisor scores in the mid 80''s are what we look for and are good indicators for excellent light performance within them. When we saw the model of this along with its GA performance numbers this demonstrated a strong contender which proved to be a fine stone.

3. Interference colors on the Gemex: We see this from time to time. In the past, for purposes of *speed* we''d post screen shots of the Gemex results without first submitting the results to Gemex, hence that was not a "Gemex approved" scan. All current and future scans are and will be, with no interference colors. Gemex is a little lenient on me since I''m one of their pioneers and allowed me to do this for a short time. Their latest software enhancement however does not allow screen shots. From what we could tell that infintesimal amount of interference had no impact on the final results when ran a 2nd or 3rd time.

 

[belle]

Date: 8/23/2005 4:06:59 PM
Author: Rhino
From what we could tell that infintesimal amount of interference had no impact on the final results when ran a 2nd or 3rd time.

as strm would say....

prove it.

run one or both of the stones showing interference linked here and post the results.
that way we can see the impact on the final results.