6 replies to this topic

[lalaji]

I have seen a diamond with the below dimensions

1.5ct
Table dept 60.7%
Table size 61%
Crown angle 34.5%
Pav angle 41.0%

The cut, sym and polish are excellent.

I heard people saying that large table diamond should be avoided. Is that true for this case? It is graded as excellent by GIA. Does that mean this diamond is at the lower end of the excellent grading by GIA? I heard that big table size will make the stone more brilliant but less firy, Is fire or brillance more important?

thanks

[LaurieH]

Lalaji,

if you're talking about a Round Brilliant, the ideal range* is 55-65%--61% puts you pretty much smack-dab in the middle of that, so you're totally fine!

Here's the rule of thumb--you don't want too small of a table, because it makes the "flash" on the top of the diamond smaller, making the diamond appear (artificially) smaller. Also, then often the crown is higher because of all the larger cuts for the facets, etc. You don't want too large a table, because then while the flash is larger, the other facets are smaller, allowing light to bounce around less, and basically creating a huge "window" into the diamond.

But, as I said...if we're talking a round, you're well within the ideal range. I actually like rounds better when they're in that middle-upper end of the ideal range, but everyone has their own preference. BUt the diamond you're looking at, you have nothing to worry about!

Good luck and congrats in advance!



*Other shapes have different ideal ranges for table percentage

[lalaji]

Hi LaurieH,

Thanks a lot for your answer,

I heard there is something called Towkowsky theoretical ideal cut. which the ideal table size is 53%-58%. I am just wonder if that is the best of the best and the 61% I mentioned is the "Less of the best"?

thank you

[davidelevi]

Couple of points:

1. What Tolkowsky did (in 1919...) was to reflect his taste and knowledge of the way diamonds are (were) cut, which as well as looking nice has to make sense economically, that is exploit the rough without too much waste. There are some good theoretical groundings to Tolkowsky's study, but at the end of the day in his conclusions there is also a reflection of personal taste. Laurie - from her posting - seems to favour diamonds with tables on the larger side; conversely I prefer diamonds with "old cut" attributes, such as high crowns and small tables.

2. Have you actually seen the diamond, or just an ad for it? If you have seen it, have you compared it to diamonds with different cut proportions? Ignore the issues of size, clarity and colour, just focus on the cut. Which pattern do you prefer? Can you see the (supposed) more brilliance and less fire?

At the end of the day, no matter what supposedly absolute metrics people try to invent to measure "beauty", it remains largely in the eye of the beholder.

[denverappraiser]

‘Ideal’ is a tricky word and it’s used very differently by different people. A lot of thought has gone into this in the last decade or so and both GIA and AGS have changed their positions on it significantly. The key problem is that a diamond is a fairly complicate prism and the behavior of light in them isn’t just a function of the angle and size of the facets, it’s a function of the relationships between these angles. Assigning a range for a particular facet in isolation simply doesn’t work. Some stones with a 61% table are lovely and some are dogs. If you’re looking at a GIA graded ‘excellent’, you’re at a good starting place but if you want to dig into it deeper you need a lot more information, not the least of which is to actually look at the stone in a variety of lighting conditions.

The reason the GIA range for ‘excellent’ is so broad is largely a function of taste and partially a function of money. Even if you take money out of the issue, not everyone likes the same things. The heart of the GIA scale was a study where they had a few hundred people look at a few hundred stones comparing one to another and asked which one they preferred. They collected several hundred thousand observations and carefully worked the stats. This is interesting enough data but it has several important scientific flaws, not the least of which is that what they are measuring is popularity, not optics. More popular is not synonymous with better. The solution was to make some broad grades that indicate that, in general, a particular proportion set is likely to be more popular than another and to assign it a name. That's ok and even useful for what it is but it's not what people generally think of when they consider the topic of a 'cut grade'.

Money comes into it because cutters have to deal with waste of both material and time. All they can do is remove material and every time they touch a stone it gets a little bit smaller. In the end they will be selling by weight so there is a constant battle over whether they should do a particular task to ‘improve’ something or just leave it alone and let it be bigger and cheaper. In the end, as I’m sure you know, otherwise similar stones sell for more if they’re bigger so the issue is whether the task at hand is going to improve the stone enough to justify the increase in price (because of the extra work) and the reduction in size. Not all will make the same decisions and not all shoppers are looking at the results in the same way but it’s not correct to describe as one being near the top of ‘excellent’ an another being near the bottom. The scale just doesn’t work that way. In the end it's ALWAYS about the money and the job of the cutter (and the seller) is to maximize the value of the final stone within the limits of the original piece of rough and the costs of whatever can/should/might be done to it.

If you want to play with the scale and how it changes when you tweak one variable or another, there’s a cool utility online at www.facetware.gia.edu.

Tolkowski is a complicated question and Davide gave a good summary above. I would add to this that there are a fair number of jewelers selling stones that are supposedly cut to Tolkowski specs that are far from it. There are labs that grade things to 'Tolkowski Ideal' that would have Mr. Tolkowski rolling over in his grave and that have his grandson, who is a first rate diamond cutter in his own right, fuming over the use of the term.

Edited by denverappraiser, 02 October 2010 - 09:51 AM.

[jan]

lalaji, on 01 October 2010 - 06:49 PM, said:

I have seen a diamond with the below dimensions

1.5ct
Table dept 60.7%
Table size 61%
Crown angle 34.5%
Pav angle 41.0%

The cut, sym and polish are excellent.

I heard people saying that large table diamond should be avoided. Is that true for this case? It is graded as excellent by GIA. Does that mean this diamond is at the lower end of the excellent grading by GIA? I heard that big table size will make the stone more brilliant but less firy, Is fire or brillance more important?

thanks

We tend to get more light return in stones with a 53-58% table. However you need more than a table measurement to do a light performance analysis. You actually need to have the stone in hand to test it. No lab report will tell you how bright a stone is. At best you will only have 4 average measurements from a lab report. Impossible to tell you how all the 57 facets will react as far a light return from a piece of paper.

Edited by jan, 02 October 2010 - 10:08 AM.

[lalaji]

Thanks for everyone's kind help!