Whose Diamonds Look Biggest?

[Superidealist]

I've searched the inventories of several online vendors and compared the spread index of their diamonds to see who cuts closest to the "ideal" of 6.50mm.

The results below show the spread indices for all diamonds between 0.50 and 1.50ct for A Cut Above, Diamond Ideals H&A, Dirt Cheap Diamonds Signature, Nice Ice, and SuperbCert and a representative selection of diamonds of the same size from Blue Nile Signature and Hearts on Fire.

 

[Superidealist]

.

 

[Superidealist]

.

 

[Superidealist]

.

 

[Superidealist]

.

 

[Superidealist]

.

 

[Superidealist]

.

 

[Superidealist]

.

 

[moremoremore]

got a lot of time on you hands, huh?

 

[verticalhorizon]

This is the geekiest thing I've ever seem on PS to date.

I love it!

 

[moremoremore]

LOL...rolling....Luv ya superidealist....

 

[noobie]

Very interesting Dave,




I note that none of the average diameters are above 6.5 mm. Is there anything else that you draw from these numbers? Looking at the graphs, I infer some things, but would be interested to hear from the "experts" and vendors. I guess most of them are in Las Vegas right now, maybe they will comment when they get a chance

 

[verticalhorizon]

It's interesting to see that HoF, one of the most expensive brands, averages the smallest for its carat weight and the largest deviation from ideal.

 

[fire&ice]

I think you may need to enter the twelve step spreadsheet progam with my husband. Step away from the spread sheet.

that said, I am surprised at how many diamonds are below the 6.5 mark. We make such a big deal about it. Maybe it really is just an average.

 

[hoorray]

Ahh the creative mind with insomnia.....interesting stats. I think the variance of some versus the tightness of the spread of others is interesting. Although none of the spreads are so wide that they're really far off the mark.

 

[pricescope]

Couple of days ago we ran some stats on the diameter of all 1ct round diamonds listed in the web.

About 1/3rd of all 1ct rounds have diameter less than 6.3mm.

 

[chialea]

wow, thanks, this is really interesting. at the very least, it lets you know who you have to be more or less careful about that sort of thing with

now if only I can figure out how to explain to my mother than hearts on fire is really not that special, and not worth the premium (given that she has an engineering type for a doting husband)... I guess my SO and I are just going to have to buy an amazingly sparkly engagement ring! no choice here at all. it's a public service.

 

[bling]

awsome! i love it...

 

[Hest88]

Interesting charts, DR. Can you narrow it down to a simpler chart, just plotting a more narrow field of, say, between .95 and 1.25?

 

[Paul-Antwerp]

Very interesting, although a bit rough.

First, one should be aware not to pay too much attention to that exact 6.5-score.

A 1.00 Ct-diamond weighs on average 1.0045 (between 1.00 and 1.009). Therefore, you come to a "ideal"-score of 6.5/1.0045 being 6.47, if all other presumptions are correct.

Also, the hidden weight in the smaller stones probably has a bigger impact on the score (being percentage-wise bigger) than in the biggest stones.

At least, in the variance, this shows a clear difference between the true super-ideals and the wannabees. After all, if you want to buy a brand, you do so because of consistency, and it seems clear that this is seriously lacking with some.

Just for fun, I quickly calculated the same for 7 Venus-by-Infinity-stones, without selecting them. Result: 5 times 6.47, once 6.49 and once 6.51, with weights ranging from 0.71 to 1.58. I must admit that I was not surprised.

Live long,

 

[aljdewey]

I'm a bit fuzzy on the information contained in these graphs. From what is plotted, it appears that you are saying that vendors are offering stones of 1.2 and 1.3 carat weight that only measure 6.5mm?




I find that hard to believe. I must be reading these wrong. My 1.24 ACA diamond meausures 6.97.

 

[dsong1]

I'm confused on how to read this. How do I know where my diamond falls for a 1ct?

 

[pricescope]

AL, Dsong1, it is not a diameter but Superidealist' spread index = (average diameter)/(carat weight)^(1/3)

I agree with Paul, although it is fun, do not be too obsessed with this. Table size difference from 54 to 58 can affect spread quite a bit as well.

 

[valeria101]

----------------
On 6/2/2004 12:01:24 PM leonid wrote:



Table size difference from 54 to 58 can affect spread quite a bit as well.----------------

How does this happen?

I thought that between two diamonds with identical depth, culet, girdle and diameter, the one with the smaller table is lighter, a bit.

 

[pricescope]

Valeria101:

----------------
I thought that between two diamonds with identical depth, culet, girdle and diameter, the one with the smaller table is lighter, a bit.
----------------

Diamond..........#1..........#2
Weight:..........1 ct.......1 ct



Table:...........58%........54%
Diameter:........6.51 mm....6.47mm
Depth:...........3.92 mm....3.99 mm
Crown Height:....14.4%......15.8%
Crown Angle:.....34.5°......34.5°
Pavilion Depth:..43.1%......43.1%
Pavilion Angle:..40.75%.....40.75%
Culet:...........Pointed....Pointed
Girdle:..........1.0%/2.7%..1.0%/2.7%

 

[squirerad]

Very very interesting

. However, I have to say that the human eye cannot differentiate sizes from 6.439 mm to 6.497 mm.

More importantly, if one uses more scientific rigors one will find that there is NOT any statistically significant difference between the most "ideal" (SuperbCert) to the least (Hearts on Fire).

The average diameter would be the MEAN and the smallest average deviation represents the STANDARD DEVIATION, which would produce the following spread results:

SC 6.473-6.509
ACA 6.478-6.516
NI 6.445-6.515
DI 6.446-6.512
BN 6.422-6.512
DCD 6.398-6.506
HOF 6.373-6.505

As you can see, taking the measurements to just one standard deviation yields no statistically significant differences in the spread of the different brands, i.e., the spread results overlap. SO those who have purchased with any of the brands above should be comforted that their diamond is just as good (in terms of spread) as any other brand.

squire

 

[Superidealist]

----------------
On 6/2/2004 10:53:26 AM leonid wrote:

Couple of days ago we ran some stats on the diameter of all 1ct round diamonds listed in the web.

About 1/3rd of all 1ct rounds have diameter less than 6.3mm.
----------------

I think this speaks to the quality of diamonds at the sites listed above, since none of the 720 diamonds sampled had a spread index of less than 6.35mm.

 

[Superidealist]

----------------
On 6/2/2004 11:22:19 AM Paul-Antwerp wrote:

Very interesting, although a bit rough.

First, one should be aware not to pay too much attention to that exact 6.5-score.

A 1.00 Ct-diamond weighs on average 1.0045 (between 1.00 and 1.009). Therefore, you come to a 'ideal'-score of 6.5/1.0045 being 6.47, if all other presumptions are correct.

Also, the hidden weight in the smaller stones probably has a bigger impact on the score (being percentage-wise bigger) than in the biggest stones.

At least, in the variance, this shows a clear difference between the true super-ideals and the wannabees. After all, if you want to buy a brand, you do so because of consistency, and it seems clear that this is seriously lacking with some.

Just for fun, I quickly calculated the same for 7 Venus-by-Infinity-stones, without selecting them. Result: 5 times 6.47, once 6.49 and once 6.51, with weights ranging from 0.71 to 1.58. I must admit that I was not surprised.
----------------

I agree, no one should take this too seriously. At best, it is a very crude indication of cut quality.

When I started out doing this, my purpose was to see if there was a difference in the spread index of diamonds just shy of and just above the 1.00ct mark. That is, to see if cutters were cutting deeper to break the 1ct barrier. Unfortunately, as you can see from the first graph, there is almost no product out there in the 0.90 - 0.99ct range, so that fell by the wayside.

Still, I think it does show something about the different lines.

If people were wondering why Infinity and Good Old Gold weren't included, I couldn't find enough of the Infinity stones to make what I thought would be a representative sample and, while there were plenty of stones listed on Good Old Gold, as anyone who has ever visited Jonathan's site will know, it takes forever for each diamond's page to load.

This is actually an extension of a similar project I did two years ago. At that time, I compared about 20 diamonds each from several vendors. Paul will be happy to know that Infinity was included and did quite well in the comparison.

 

[Superidealist]

----------------
On 6/2/2004 3:14:49 PM squirerad wrote:

Very very interesting

. However, I have to say that the human eye cannot differentiate sizes from 6.439 mm to 6.497 mm.
----------------

Differences become increasingly significant as carat size increases.

 

[Superidealist]

----------------
On 6/2/2004 11:11:57 AM Hest88 wrote:

Interesting charts, DR. Can you narrow it down to a simpler chart, just plotting a more narrow field of, say, between .95 and 1.25?
----------------

If you're interested, let me know and I'll be happy to email you the file.