dark areas in very bright lights

[USC]

Hey, I loved reading all your posts so I had to join. Quick Question...Why do I see dark areas in my Princess Cut Diamond. It is great looking in jewelry stores and in regular office lighting. But on stage under bright lights or in direct blaring sunlight (it''s been so sunny abd hot in Florida) I see dark areas. Is it leakage? It still sparkles, but doesn''t look as white. Here are the specs.
measurements 7.61x6.95x5.00
Weight 2.11
Depth 71.9
Table 74
Girdle Med
Culet None
Polish/Symmetry VGood
Clarity Vs1
Grade G
Flurescence Faint

Also, for you professional diamond experts, what is a fair price for this piece? Thanks for your help and advice.

 

[Nicrez]

I am assuming that these are not Scintillation sparkles, but maybe dark spots towards the center of the stone, on either side of the culet, shaped sort of like a bow-tie?

Also, i think from just the Table percent (and no angles or crown height) i am guessing it could also be that the larger table causes a bit of a large sparkleless facets, which could be light leakage...

Here's what PS says on tables that are disproportionate: "Scintillation is the other casualty of a large table. Scintillation is hard to define, it is the black – white – black flashing you observe as you roll a diamond (or move the light source). If a diamond had no crown facets it would appear boring." See full article on THIS PAGE

Either way, if it's seen head on, all the time, it's not so good, BUT if it's just when you look down at it on a 45 degree, it may not be too bad, because your stone appears larger than the weight would normally...so it could be a good buy on your part and just a characteristic of your stone!

I hope this helps somewhat...Good luck and enjoy your stone!!!

 

[caratgirl]

Hi USC, I suspect that the dark areas are the ones that reflect the most light - in well cut round stones, almost the entire stone looks dark in that type of light. So...that is a good thing, not a bad thing.

 

[valeria101]

The dark areas that end up reflecting light allot show black under the Iscope... those that do not have this gracious quality show white.

So... the topic you mention (dark areas in stone) would be discussed when the reading of Iscope ismages is. You might want to check either the Iscope site (LINK) or the explanation on GOG (LINK).

There is some discussion on what the black and white areas or total reflection and light loss do to the overall appearence of the stone, so there is always too much of a good thing (too much black) and too little of a bad

(no white also means less contrast). This is a tad in the 'hair splitting' domain, given that princess cuts with decent overall light return are hard to identify anyway

...

Hope this helps

 

[Nicrez]

question: Today I saw a whole bunch of BIG Square cut emeralds, and I noticed that they looked very dark. (LOTS OF DARK SPOTS) What does that mean...? They did look very deep...somewhat shallow crowns...

 

[valeria101]

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On 4/30/2004 3:00:31 PM Nicrez wrote:

question: Today I saw a whole bunch of BIG Square cut emeralds, and I noticed that they looked very dark [...] very deep...somewhat shallow crowns...

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There must be some free version of ray-trace software for you to play with Nicrez

It sounds like the answer is right there in your post, and there might be two of them, actually:

#1: overly deep pavilions are also steep, so light would escape when reflected onto them from one side of the pavilion to the other.

#2: flat crown might mean a couple of things, but here I would imagine the tables were also large. If so, the small and steep crown facets would also send light down the drain (down to escape through the pavilion that is) under them and kill sparkle towards the edges of the stone.

But... but, who needs sparkle in an EC anyway! Those are the nicest whatever they do to light

 

[Nicrez]

My lord though they were gorgeous little animals! I tried on a 3.45ct Square emerald...*sigh* and i have to say that oddly, for something THAT much heavier than my 1.73, it really didn't look THAT much larger than mine. Granted it was, but not DOUBLE, definately not...I guess it was all in the pavillion!

I know I have a large table, but I anticipated a larger difference to the eye.... This makes me VERY happy...

Oh and Ray Trace software....WHERE CAN I GET IT?! Honestly.

 

[valeria101]

Ray trace...

well, unless you want to get the respective DiamCalc, GemCad (LINK) is available for a 30 day trial for free. More than enough if this should be bed-time reading into why and how gems are cut. GemCAd is not made to suit diamond RI only, - hence the endless quantity of notes on why, where and how it works or doesn't. It is less fancy, but c'mon, nice to play with.

The problem you mention with the ECs gets discussed in principle by the GemCad users manual (page 42 onwards).

The piece does not discuss dispersion (fire) and contrast much, but does so with total light return and teh famous sensitivity to 'obstruction' (head shadow). One can work out contrast between the lines and as little as a run through the by now fabled and publicly available Tolkowshy paper (LINK) may help add sophistication.

I would bet there is another dozen of such applications somewhere

For me is just pen, paper and comapss, I am affraid...

 

[valeria101]

Nicrez... your EC size note just got into the geometry homework of my little cousin here

it sounds that a rad with twice the mass of yours, would have 1.25 times the size (area face up, given the same depth percentage, whichever it is).

 

[Nicrez]

interesting...goes to show how sometimes the cut can make the size, and NOT the carat weight....hmmmm....

As for Gem Cad, I have put that on my Wish List, but sadly it's is only populated by me. Come anniversary, birthday, Christmas or Groundhog's Day, I will be releasing the list to my loved one, so he can choose how best to make me happy. Gem Cad is just below diamond tiara...

 

[valeria101]

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On 4/30/2004 4:52:24 PM Nicrez wrote:



interesting...goes to show how sometimes the cut can make the size, and NOT the carat weight....hmmmm....

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Well, somewhat. It is easy to workout the tradeoff of depth for carats: not a linear function, but easy enough to get a ballpark rate for each reasonable weight interval.

Between 2.5-3.5 cts, about 4% variation of depth 'compensates' for 0.3 cts - for what is that worth. However, keeping that depth reasonable (65%-75%, I guess), there is just not much room for such trade-off

but a good half a carat gets easily hidden by cut.

I wander where size differences start to show - I am definitely blind to splits of a milimeter