Alternate analysis/valuation: diamond surface area?

[Defender]

As a newbie, trying to make a choice among a wide array of stones with differing weights, I have learned how hard it is to make comparisions based on carat weight alone. I have seen larger carat weights with less surface area, along with lighter stones with more surface area. For example, I have seen 2.4 carat stones with surface area rivaling deeper 3 carat stones. We are talking about nothing new here..it is just a matter of the spread.

In my own silly way, I have started to compare stones by surface area....After all, the "face up" size of a mounted stone is the actual view that most of the world will have.

Of course the brilliance and visual quality of the face up view is the key issue, but the visible surface area is really what the real world sees. So, am I crazy if to make some effort at comparison based on surface area?? .....I have to believe that I am not the first one to try this type of analysis

 

[strmrdr]

nope your not the first...

do a search for spread index
lol

 

[strmrdr]

btw just buying based on the most surface area can get you a bad diamond.
so dont go too far with it.
If it scores 1 to 2 on the hca then its kewl if not then there are other things to check.

 

[kenny]

Wouldn't a diamond cut as flat and thin as a piece of paper have the highest surface area for its weight?

And wouldn't a perfect sphere have the lowest surface area for a given weight?

Neither has any desirable optical performance.

I'm not sure what surface area has to do with bling.

 

[oldminer]

We can grade PERFORMANCE and SURFACE AREA of round, princesss and marquise shaped diamonds. I would suggest you use surface area only to compare diamonds with similar light performance, but it IS a very useful concept which will grow over time. Being able to measure the face-up view of the diamond, the area inside the outline of the girlde has become much more easy with the advent of digital measurement. I don''t believe any other lab offers this service although should I be incorrect, someone will tell you I''m wrong on this. People should consider high performance combined with best visual size when it is possible to do it.

 

[valeria101]

Date: 3/29/2006 12:22:37 AM
Author: kenny
Wouldn''t a diamond as flat and thin as a piece of paper would have the highest surface area for its weight?

But it would have no bling.

Well... keep the other known parameters within reason and that should help avoid monsters.

The fun part is that with fancy shapes (you were looking at emerald cuts, no?) total depth is not the only thing affecting spread allot. So looking at surface area is more practical than looking at the depth % in the hope to guess whether one or another diamond is large for the weight.

With so many diamonds listed online it is quite easy to figure out some reference - what is good or bad ''spread'' for a given shape and weight. Sure enough, it doesn''t make sense to pick the largest regardless (say, 30% deep marquise.. or declare rose cuts the best of them because they are the most flat): a pinch of judgement, and things should work out.

 

[valeria101]

Date: 3/29/2006 7:16:22 AM
Author: oldminer

Being able to measure the face-up view of the diamond, the area inside the outline of the girdle has become much more easy with the advent of digital measurement. I don''t believe any other lab offers this service ...

The diameters give a good hunch: for... marquises or pears is a bit of a pain, but how much precision is needed anyway?

Wondering if some reference for an interval of ''good size for weight'' could be attached to the AGA tables.

I am aware of the inherent approximation, but also believe that any useful result achieved with the readily available data is good to have.

 

[kenny]

I edited my post to try to make it more clear.

When you guys say surface area are you just talking about spread (diameter for a given weight)?

I ask because surface area of a, box, a pyramid, or a diamond would logically mean all surfaces added together.

 

[Defender]

I am not so naive to ignore the other basics of a good stone.

I was not trying to suggest that surface area means everything. I am trying to compare stones of comparable quality--- However since these all have differing proportions, l/w ratios, and surface size, it can be confusing. I know that I am really talking about an issue related to spread, but I was simplistically just looking at surface area.

The best example that I can give is that I was comparing two stones with similar clarity, color, depth, table, and crown. However, the length and width ratios and actual sizes vary from stone to stone. On paper it was hard to see much...Absent the ability to view them both, I calculated the surface area of each and one was clearly larger in face up position. In a mounted stone we all see the apparent size of a diamond in this way, so it seems like another way of judging these things--especially when shopping online.

For a newbie, it illustrates spread in a very basic way, when you see that some 2.5 carat stones appear as big as other 3 carat examples

 

[kevinyonker]

The HCA grades spread.

 

[oldminer]

We can now measure, with great accuracy, the square millimeter area enclosed within the girdle plane of a round, marquise or princess cut diamond. In time, all the other shapes will also be able to be measured.

This measure of visual size, when combined or put into a ratio with carat weight will yield information that previously was not generally available. People have been asking for years, "Which diamond looks larger?" We really had no way to know when it came to marquise shapes or when comparing a marquise to a round or a princess. Now we have a relatively easy way to discern the visual size answer.

Up to now, people relied on "depth percentage" to give a pretty good clue about viausl size alogn with lenght and width measures. However, the new cutting of AGS 0 princess cuts results in diamonds which depth percentage does not well describe if non AGS 0 princess cuts are being compared. The bulge of the pavilion differs and weight to spread relationships are altered. For this reason it will be much better to get square millimeter size and make some ratio to weight.

 

[valeria101]

Date: 3/29/2006 9:51:27 AM
Author: kenny

When you guys say surface area are you just talking about spread (diameter for a given weight)?

I ask because surface area of a, box, a pyramid, or a diamond would logically mean all surfaces added together.

Err.... vertical projection on the girdle plane

 

[denverappraiser]

If we were to start from scratch and try to design a diamond grading system without the benefit of knowing how GIA has done it and describing things in a way that the consuming public seems to value, the item to be maximized would seem to be beauty/sq.mm. Weight would be irrelevant. Beauty is a tad difficult to define and it’s not generally the same throughout the stone in any case so there would need to be some sort of beauty distribution variable as well. It also seems like a problem that the expected incremental cost for an extra few sq.mm.’s of beauty on a 15mm stone is quite a bit more than it would be on a 4 mm stone so we would need some sort of variable for that. It might be an entertaining academic exercise, sort of like non-Euclidian mathematics but something tells me that the diamond world is unlikely to adopt it. How about:

Face up area
Outline
Brilliance
Scintillation
Dispersion
Distribution
Hue / Saturation (including fluorescence)
Transparency
Durability
Symmetry
Neil Beaty
GG(GIA) ISA NAJA
Professional Appraisals in Denver

 

[valeria101]

Date: 3/29/2006 5:00:41 PM
Author: denverappraiser

If we were to start from scratch and try to design a diamond grading system without the benefit of knowing how GIA has done it and describing things ...

They did rounds... thre''s more.

And it looks like the one lab that looks interested in grading the cut of everything (AGS) would not allow comparing shapes into the design of their grading.

... perhaps there is still room for indie cut grades after all

 

[denverappraiser]

I think color and clarity would both be done quite differently as well.

For example, for most customers, clarity is only relevant to the extent that it affects the beauty of the stone and within the lower grades, I1 & I-2, the difference between the worst and the best within a grade can be visually very important while the difference between IF and VS-1 is irrelevant. I don''t think the current method accurately tracks what customers find makes one stone more valuable than another.

Neil Beaty
GG(GIA) ISA NAJA
Professional Appraisals in Denver

 

[valeria101]

Date: 3/29/2006 5:19:53 PM
Author: denverappraiser


I don''t think the current method accurately tracks what customers find makes one stone more valuable than another.

So agreed!

The Net makes for a mine of buyers'' opinions much along these lines. Hope someone would find the matter interesting enough to add the evidence up in an inspiring two lines

 

[Defender]

The focus on carat weight can make things a bit silly for the average ring shopper. I think that some people worry about getting a stone that may meet their fiance''s expectations based on carat weight, rather than dealing with the actual visible size of the stone.

Folks do not discern these things unless they get educated.... or hang around a place like Pricescope!