Find your diamond
Find your jewelry
shape
carat
color
clarity

Naive question on light properties of diamond

bose

Rough_Rock
Joined
Jul 21, 2016
Messages
22
i have read some posts on ideal proportions of diamonds and light properties, as well as on testing diamonds with HCA (to weed out) and idealscope.

my question is: suppose you have two GIA XXX diamonds next to each, one is very good in HCA/idealscope, the other one not so much. suppose all other properties are the same (say F colour, VS2 clarity, 1 carat size, to be concrete).

is the difference between these two obvious to the (average) naked eye? will the better one sparkle more? a lot more?

i'm just trying to get a sense of how important the HCA/idealscope results really are in practice (for someone interested in buying a ring).

thanks!
 

Rockdiamond

Ideal_Rock
Trade
Joined
Jan 7, 2009
Messages
8,173
Great question Bose!!

It's a question of degree. There's a lot of combinations that get "dinged" on HCA that can look amazing in real life- well cut stones that are slightly different than what HCA will grade as under 2- different, but still super well cut.
There's also badly cut stones. You're not going to find many badly cut GIA EX Cut grade stones- they do exist, but they're quite rare.
 

John Pollard

Ideal_Rock
Trade
Joined
May 1, 2008
Messages
3,559
Rockdiamond|1469212177|4058382 said:
You're not going to find many badly cut GIA EX Cut grade stones- they do exist, but they're quite rare.
Admittedly, what I consider badly cut isn't in-line with the opinion of many jewelry professionals, but over the years I've found it to be in-line with the opinion of many or most consumers spending thousands of dollars on a diamond. In that sense, I see plenty of badly-cut EX.

Context: Unlike top color or clarity grades (think D-E or VVS1-VVS2) the industry's top cut grades embrace a wide range of looks. Using GIA as an example, "D color" is pretty much D color wherever you look. However the single grade "GIA EX" embraces a wide range of different makes and performance levels.

Makes: Ideals, 60-60s, shallows, deeps and transitionals are all possible within EX. Setting performance aside, all can be extremely beautiful. Their different parameters translate to different balances of brightness vs fire in overall optics, the median size of visible scintillation and other (arguably subtle) details. Assuming top performance in all, a viewer's eye for detail and personal preferences will determine which, if any, are favored over the others.

Performance Level: If I were to plan a single diamond for my wife I would ensure that it was cut with the optimal physical geometry, angles (and 3D precision, but that's another topic) for top performance within its make. Unfortunately, that's not the way diamond output occurs. Every crystal is planned for best yield within a grade. And, with such a wide range of angles capable of achieving "EX" there's no motivation for mass-producers to produce at the high end of performance. Simply put; what "EX" will get us the best yield? For the world at-large that might not matter, yet it does to some.

Examples: Below are ASET renderings for 4 practical diamond proportion-sets. All 4 would earn GIA EX from their basic proportions. And while they'd all sparkle nicely under bright jewelry store spotlights, those at the bottom would look notably smaller at the edges and center in normal and low lighting conditions. You must decide if that matters to you or not.


You may have seen Pricescope consumer enthusiasts here requesting ASET or Ideal-Scope images to better assess basic diamond performance. These light-return images are a definite asset (haha) and are something of a prerequisite for meaningful feedback here.

With that said, there are components observed in live performance which 2D ASET and H&A images do not reveal. In that sense, while the input here may be interesting to consider, your eyes will always be your best ally.

aset-taxonomy.jpg
 

flyingpig

Ideal_Rock
Premium
Joined
Nov 7, 2015
Messages
2,171
bose|1469210272|4058373 said:
is the difference between these two obvious to the (average) naked eye? will the better one sparkle more? a lot more?
Yes. The difference maybe subtle at first. But if you own an ideal cut diamond and wear it often, you slowly learn how a diamond should perform in different light conditions. Before you know it, next time you walk into a mall or even boutique store, you will notice your ideal cut stone just trumps anything they can offer.
 

Madison2

Brilliant_Rock
Joined
Jan 27, 2012
Messages
507
flyingpig|1469228057|4058452 said:
bose|1469210272|4058373 said:
is the difference between these two obvious to the (average) naked eye? will the better one sparkle more? a lot more?
Yes. The difference maybe subtle at first. But if you own an ideal cut diamond and wear it often, you slowly learn how a diamond should perform in different light conditions. Before you know it, next time you walk into a mall or even boutique store, you will notice your ideal cut stone just trumps anything they can offer.
+1
Yes, absolutely can relate to what flyingpig is saying. I own a ideal round brilliant diamond ring and most recently while in St. Martin on vacation, whenever I went into a boutique or jewelry store, I was told "your diamond is gorgeous, beautiful, etc. even customers who were in these stores saw my ring on my finger were staring at my diamond and many said to me, you have a beautiful diamond.
I would go into coffee shops and even there where the lighting was dim, the server said to me at check-out, wow your diamond is gorgeous.
I wear it proudly and I am most grateful that I got the best cut round brilliant diamond and went through the process of HCA/Aset Images to confirm I was getting the best cut diamond for my budget.
 

bose

Rough_Rock
Joined
Jul 21, 2016
Messages
22
thanks a lot for all for your answers! particularly for John's detailed one. that's helpful to know, i think i will look for a great cut then. it's too bad that jamesallen cannot provide IS images for any of the 4 diamonds i inquired about...

still interested in any further opinions!
 

LLJsmom

Ideal_Rock
Premium
Joined
Oct 24, 2012
Messages
9,257
Yeah. The bummer is that for an inexperienced person (I consider myself that compared to so many PSers who have been looking at diamonds for years.) he/she will only notice the details of how a diamond performs after wearing it for a pretty long while. You see after days and days Of wearing it in different environments the spots on your stone that don't light up the way you want it to. Picking the best cut stone when you first buy by using all the resources out there (ASET images and opinions of experienced PSers) is the best way to minimize the likelihood of finding that your GIA 3X isn't so great after wearing it for a year. Investigate all your options. You want to see a light show? Check OECs old European cuts and August Vintage rounds, cushions, Canera antique cushions... Those cuts will blow your mind. Just saying. If I knew hen what I know now....
 

ChristineRose

Brilliant_Rock
Premium
Joined
Aug 5, 2012
Messages
926
AGS used a formula to determine the 0 grade. There's a lot to it, but the short part is that face up, white light return has to meet a certain high threshold.

GIA got a whole bunch of diamonds and showed them to a whole bunch of people, and asked them which ones they liked best. They made maps of the proportions of the diamonds, and any diamond that falls into the right proportion gets an Excellent.

So both start with a range of proportions, but the ranges came from very different places.

There are big problems with GIA Ex. One is that just because somebody liked a diamond, it doesn't mean you will like it. The range is so large that it's almost a given that they'll be a GIA Ex which you think is "worse" and one that you think is "better" and this is obviously not something you can tell from the grade. The cuts are unpredictable--there are a lot of things that go into a diamond. For instance, you might sacrifice brightness for flashes of color, or for a pattern (150 years ago diamonds were expected to look like a weird crystal flower).

Another problem, which is perhaps the biggest, is that the majority of diamonds now are cut to be right on the border of the GIA Ex range so you're looking a lot of diamonds cut to fit the taste of someone who likes something other than maximum light return.

If you wish to buy online to save money, you should learn to use tools like the Idealscope. Or you could work with one of the high end dealers who can walk you through all these nuances. If you just want the best possible face up white light return you can look for an AGS 000 in your price range and not worry too much about it.
 

flyingpig

Ideal_Rock
Premium
Joined
Nov 7, 2015
Messages
2,171
https://www.youtube.com/watch?v=cY8hbvtdXMs

The diamond on the right has the following proportions: 58/61.6/35/41. This is actually more than just decent for a common GIA XXX. When you look at the individual numbers, all fall within the orthodox ideal ranges of 54-58/60-62.3/34-35/40.6-41. However, 35 crown and 41 pavillion are not complementary and HCA shows this with a score greater than 2.0 (also it is outside AGS ideal proportion range). Look how the contrast (arrows) pattern is irregular and washed out; very typical of 35/41 combo. Because of this, the diamond lacks bold fire from the arrows in spotlighting condition, and lacks clear contrast/brightness pattern in regular office lighting condition. I am sure it is still beautiful in real life; it is a diamond and it is still GIA XXX. But right next to an ideal cut stone, it is not thrilling. In term of where it places in the AGS ASET chart John provided you, I would say maybe AGS1. But I am not an expert.

To make things more complicated, 35/41 combo can be good, dependng on the acutal angles. GIA rounds numbers alot. That is where the IS image is helpful and you cannot fully rely on HCA.
 

Rockdiamond

Ideal_Rock
Trade
Joined
Jan 7, 2009
Messages
8,173
As John said- his opinion ( which is informed and certainly valid) is not in line with many other professionals. The reason is that there is personal taste involved. There are truly well cut diamonds that one person prefers and another will not.
Put another way: you may very well prefer a diamond that some others would not. For example- some people like well defined hearts and arrows patterns and others do not.
By all means look in person if you can.
 

bose

Rough_Rock
Joined
Jul 21, 2016
Messages
22
the youtube video flyingpig posted is exactly what i was hoping for! it shows clearly that there can be a noticeable difference between GIA XXX diamonds. thanks a lot!
 

flyingpig

Ideal_Rock
Premium
Joined
Nov 7, 2015
Messages
2,171
If you find it useful, then..
https://www.youtube.com/user/DiamondInfoMan
GOG has very informative videos.

FYI. These videos online are made by diamond vendors. The main purpose is to promote their business. In some videos, diamonds are strategically selected, and lighting conditions are manipulated to highlight the product they want to promote. Often, difference is rather exaggerated. Just be selective. No attack on GOG, otherwise I would not have posted the link. This just applies all "education" videos for all industries, made by sellers
 

fair75

Rough_Rock
Joined
May 28, 2015
Messages
87
Real-life light performance of a diamond depends on a lot of factors and certain personal tastes, like what others have said. But one thing that always stays true is the optimal ranges of cut. Many people would say that crown angle between 33.5 and 35.5 & pavilion angle between 40.6 and 41 are ok, as long as ideal scope and ASET scope images are good. That is true to some extent. If you prefer maximum brilliance, then fire in a diamond would be sacrificed and vice versa. A super-ideal diamond means that it will have the best BALANCE of fire, brilliance and scintillation if it is cut within certain parameters. CA 35 and PA 41 can result in a beautiful diamond, but only if it is precisely cut. The reality is most of the diamonds with that combo are poorly cut, and PA 41 is the point where light leakage starts to occur. Moreover, some people argue that a shallower crown angle like 33.5 is ok with good scope images and a complimentary pavilion angle. While that can be true, but people need to realize that shallow crown angles will for the most part reduce fire you see in a diamond, provided that everything else is equal. With that said, if you are the kind of person who wants more fire, then you certainly wouldn't want a diamond with a shallower CA.

You may have seen a lot of diamonds online that are steep and deep but are still considered GIA triple excellent, including CA >= 35 and PA >= 41 when you search for diamonds. That is because the most important factor most cutters consider is profit. So they would try to push the envelope and still get GIA triple excellent. So my personal preference is to stay in the optimal ranges of CA 34-35 and PA 40.6-40.8 when I buy diamonds. Surprisingly, I noticed that diamonds with ideal CA and PA don't cost more than many steep-and-deep ones. You just need to do your homework before purchasing.
 

bose

Rough_Rock
Joined
Jul 21, 2016
Messages
22
thanks! and good point, a video from an unbiased source would definitely be more trustworthy...
 

Rockdiamond

Ideal_Rock
Trade
Joined
Jan 7, 2009
Messages
8,173
bose said:
thanks! and good point, a video from an unbiased source would definitely be more trustworthy...
This is a great point bose.
I have yet to see a video about diamonds that did not have an agenda. Including mine.
People are warned about deceptive store lighting. The first video posted did show what the producer wanted. But I would never look at a diamond under those conditions.

Fair75- part of the debate that I find fascinating is what the balance between fire and brilliance should be.
It's like trying to decide exactly how spicy a sauce should be. Sure, there are tolerances. But within those tolerances there's acceptable variation. Spread is also a critical aspect.

The point about cutters motivation- does anyone believe cutters who do everything to get their stone to super ideals don't have profit in mind?
Not that it's a bad thing and I'm all for the best cutters getting top dollar. But looked at critically, maximizing profit is an essential element for any cutter. The best ones have additional motivations which I totally respect- but everyone has to consider bottom line.
 

flyingpig

Ideal_Rock
Premium
Joined
Nov 7, 2015
Messages
2,171
Rockdiamond|1469375836|4058820 said:
The first video posted did show what the producer wanted. But I would never look at a diamond under those conditions.
Yea. I agree. I was a bit hesitant of posting this video for the exact same reason. Those conditions are hard to reproduce in real-life and that's not how we view diamonds. I posted, however, because, at least, the producer did not choose a stone with completely trashy proportions. Yeap, I have seen videos where producers pick stones that barely make to GIA X ( overly large table, shallow crown, ) and put them under light conditions that highlight the contrast only, and say "look how dark it is"... The common GIA X shown in the video is a reasonably good stone, at least based on the proportions/report.

My point was that a normal person can notice difference between an ideal cut diamond and a common GIA X with non-ideal proportions. And the video visualizes it, although somewhat unfairly..
 
Be a part of the community It's free, join today!
    Three-stone engagement ring upgrade
    Three-stone engagement ring upgrade
    Vintage OEC Bracelet
    Vintage OEC Bracelet
    June’s Birthstone Trinity
    June’s Birthstone Trinity

Need Something Special?

Get a quote from multiple trusted and vetted jewelers.

Holloway Cut Advisor



Diamond Eye Candy

Click to view full-size image.
Top