How much more $ is a better HCA rating?Urgent advice needed

[Rockdiamond]

Re: How much more $ is a better HCA rating?Urgent advice nee

Karl- the problem I see is using anecdotal evidence to draw global conclusions
.
IOW- someone posts "I saw a stone with twining wisps and it was cloudy, therefore stones with twining wisps are cloudy"
If someone is trying to buy a diamond , sight unseen, off a list, then percentages might matter.
However percentages mean nothing if a person is examining individual examples.

What percentage of SI2 diamonds is eye clean?
Clearly, the answer will depend on where one is looking. I see a lot of eye clean SI1 and Si2 diamonds- in sizes above 2cts- sometimes much larger.
But no matter what the answer is, it's irrelevant to any single example.
Or, to use Karl's analogy- If someone just won $25,000 playing craps, they don't really care what the odds are going to be the next time they place a bet.
For someone who's found an eye clean SI stone, the percentage of Si stones that are eye clean is irrelevant.
Imo, warning them after the fact can place a doubt in someone's mind needlessly.

With regard to the dreaded "leakage" in GIA EX cut grade diamonds- and how it relates to cfl lighting: Is there any diamond that performs equally as well in any lighting condition?
IMO, no.
Therefore warning about how a GIA EX cut grade stone might have dark areas under the table in cfl is also, IMO, a misplaced warning unless it's placed in context.

 

[Karl_K]

Re: How much more $ is a better HCA rating?Urgent advice nee

David you can twist my words anyway you want but that is not what I said.

Nelly,
Sorry for the drama in your thread. David and I tend to lock horns over his agenda from from time to time.
The simple fact is no one here can give you rock solid advice about this stone without looking at it in person.
There are too many questions that can not be answered online about it.

Karl

 

[Rockdiamond]

Re: How much more $ is a better HCA rating?Urgent advice nee

Karl- I agree with your statement- no one who has not seen a given diamond can give accurate advice about that specific diamond
This holds true in all cases
Nelly- what this means is that you need to use your eyes - and your judgement about the different sellers
My only "agenda" in this thread is to prevent you from getting discouraged about a diamond based on insufficient evidence

 

[denverappraiser]

Re: How much more $ is a better HCA rating?Urgent advice nee

[quote="crbl999|1318455104|3038814

When you're in-store be sure to compare several stones in different types of lights - there is a surprising variety in-store! Have them clean all the stones (and then be sure not to touch them without tweezers!), then take them around and look under the spotlights in the counters of course, in the diffuse back-office lights, in a beam of direct sunlight by a window.

This is never a good test because most of the best cuts perform badly in such lighting

I haven't read this entire thread but I have to disagree with you here Garry. It's correct that most stones perform badly under these conditions but the point of the testing process is not to see how a stone performs under conditions that make it look it's best (at least these isn't the customers objective. It may be the dealers'). The goal is to see how it looks in as many circumstances as possible and, to the extent possible to replicate how it will look under 'normal' wearing conditions. This includes looking at it under crappy light.

 

[denverappraiser]

Re: How much more $ is a better HCA rating?Urgent advice nee

With regard to the dreaded "leakage" in GIA EX cut grade diamonds- and how it relates to cfl lighting: Is there any diamond that performs equally as well in any lighting condition?

Foilback rihnestones have 0% leakage in all lighting conditions. This is not evidence that they are 'better' than diamonds.

 

[Budgiesmuggler]

Re: How much more $ is a better HCA rating?Urgent advice nee

Nelly have you tried asking any of the Aussie jewelers whether they can order you the US stone based on the report number? I've found that the Aussie online sites have the same stones as some of the US sites, so this may be possible.

 

[Garry H (Cut Nut)]

Re: How much more $ is a better HCA rating?Urgent advice nee

[quote="crbl999|1318455104|3038814

When you're in-store be sure to compare several stones in different types of lights - there is a surprising variety in-store! Have them clean all the stones (and then be sure not to touch them without tweezers!), then take them around and look under the spotlights in the counters of course, in the diffuse back-office lights, in a beam of direct sunlight by a window.

This is never a good test because most of the best cuts perform badly in such lighting

I haven't read this entire thread but I have to disagree with you here Garry. It's correct that most stones perform badly under these conditions but the point of the testing process is not to see how a stone performs under conditions that make it look it's best (at least these isn't the customers objective. It may be the dealers'). The goal is to see how it looks in as many circumstances as possible and, to the extent possible to replicate how it will look under 'normal' wearing conditions. This includes looking at it under crappy light.

Hi Neil,
Try it with various cuts on a sunny day - often the worst cuts perform best.

 

[denverappraiser]

Re: How much more $ is a better HCA rating?Urgent advice nee

I have, and I agree, but that doesn't mean it's not a fair test just because it doesn't lead to the popular conclusion. Overall, AGS0 and GIA excellent stones look better under most lighting conditions than, say, AGS7 and GIA-fair, but calling the conditions that favor the outliers somehow unfair is in itself being unfair.

 

[Garry H (Cut Nut)]

Re: How much more $ is a better HCA rating?Urgent advice nee

I have, and I agree, but that doesn't mean it's not a fair test just because it doesn't lead to the popular conclusion. Overall, AGS0 and GIA excellent stones look better under most lighting conditions than, say, AGS7 and GIA-fair, but calling the conditions that favor the outliers somehow unfair is in itself being unfair.

I made this demo using a very small (1.8 degrees which is much larger than the sun) light source with DiamCalc.
I tilted the stones by 2 degrees so there was no table flair. They are mostly DC default stones all at 1ct size.
I am sure you would agree that all these stones would have 10 to 20% less light return than rounds and would not look as bright?

Because these cuts all have more internal bounces they have more sparkles, some of which will even appear brighter than in rounds.
Of course cuts like baguettes may only have one very bright flash because they have less virtual facets.

So I believe looking at any cut in direct sunlight has no validity as a test of anything other than a way to represent virtual facet numbers.

BTW if I really wanted to make this point - I would have represented just various round proportions - some of the very deep and very shallow stones just go crazy!
If the round and other shapes shown is not convincing - I will make movies Neil.
Of course actually looking at or filming real stones is better - but it is bad for eyes and bad nearly impossible for a camera to capture also. I did make a movie some years ago to show this effect https://www.pricescope.com/node/110155 but I hope you agree DiamCalc is a better more controlled way to show these effects.