HCA tool below 1

[Getupkid]

Why is there a note one the hca tool that says “Scores of 0-1 are often good for earrings and pendants, but usually not as good for rings.” Why would a diamond with more light return, fire and scintillation not be good for a ring?

 

[rockysalamander]

Read this. https://www.goodoldgold.com/consumers-guide-hca

PS'ers that use HCA, and many don't, simply use it as a rejection tool to narrow the pool of candidates. It is true, however, that there are also quite a few angle combinations under 1.0 that won't make GIA or AGS's top grade. In any case, once you see a number under 2.0, the real analysis begins. You have to look at inclusions, other angles, IS, ASET, H&A, etc. and overall performance to determine which are worthy of pursuit -- it still may not be worth buying in the end.

 

[uffda]

Read this. https://www.goodoldgold.com/consumers-guide-hca

PS'ers that use HCA, and many don't, simply use it as a rejection tool to narrow the pool of candidates. It is true, however, that there are also quite a few angle combinations under 1.0 that won't make GIA or AGS's top grade. In any case, once you see a number under 2.0, the real analysis begins. You have to look at inclusions, other angles, IS, ASET, H&A, etc. and overall performance to determine which are worthy of pursuit -- it still may not be worth buying in the end.

That's a lot of reading! I skimmed through it pretty good but still wonder if a diamond that scores 0-1 on HCA, has a decent IS and ASET, and no "deal breaker" inclusions should be avoided?

 

[OoohShiny]

HCA is a rejection tool, not a selection tool. The aim of it is to enable internet shoppers to narrow down the vast list of stones for sale in the world - anything under 2 on the HCA is worth consideration and, if IS/ASET/clarity all check out on paper, the stone in question can be inspected in person, either in a shop (if ordered from a shop) or at home (if ordered online from a vendor with good returns policies).

 

[rockysalamander]

HCA is just for widdling out a large pile of choices into a smaller pile of choices. Once the stone is under 2.0, you then ignore the HCA from that point on. A good IS or ASET trumps the HCA. The particular angles will generate differnt 'looks' for diamonds (e.g., 60/60, firey, white light return, tall crown, flat-top). Most PSers will tell you about these differnces.

 

[John P]

Why is there a note one the hca tool that says “Scores of 0-1 are often good for earrings and pendants, but usually not as good for rings.”

Scores 0-1 are regularly returned for shallower basic geometry. Diamonds with shallow angles show more darkness from obstruction when viewed close-up (shadow created by the viewer's head). This is especially true when pavilion angles descend beneath 40.4 degrees. Earrings and pendants are not typically viewed up-close like diamonds in rings - so viewers' heads typically stay farther away - so there will be less darkness caused by obstruction when mounted that way.

Why would a diamond with more light return, fire and scintillation not be good for a ring?

As others mentioned, the HCA is a rejection tool. It gives interesting hypotheses, but contextually the tool is drawing a "chalk outline" of the diamond's table and averaged 2D crown-pavilion relationship, and using this imagined outline to predict how basic light return will happen. In a macro application the 0-2 (etc.) numerical result is reliable. However, the further micro speculations HCA makes about fire, scintillation, etc. are generalizations. The "chalk-outline" may correlate to a basic geometry assumed to promote or reduce dispersion, but the HCA has no idea about 40 of the diamond's 57 facets, nor does it account for degree of 3D cut-precision, brillianteering/indexing details or other factors which influence character.

Bottom line? Exactly what the creator stipulates: "Remember my Cut Adviser is a rejection tool to weed out potentially poor performing diamonds." After that, seek more actual information on candidates you decide to pursue.

 

[Karl_K]

Sir John is correct when the pavilion angles get below 40.45 there is a cliff where obstruction greatly increases. It is some what increased at 40.5 but with tight cutting to make sure they don't drop off the edge can be great.
That is why many systems stop at a 40.6 pavilion for most combinations.

The greater viewing distance in ear rings and pendants compensates for this.
Garry the inventor of the HCA likes these diamonds(so do I) and includes them in his potentially good diamond range.
Other grading systems are ring centered and downgrade them.

 

[Karl_K]

As an aside there are 2 cliffs for diamond pavilion mains for a modern RB less than a degree apart:
40.45 obstruction and 41.38 color retention.

 

[Getupkid]

So a diamond with a pavilion angle at 40.8 that is below 1 on HCA still might be alright at close distance?

 

[flyingpig]

So a diamond with a pavilion angle at 40.8 that is below 1 on HCA still might be alright at close distance?

Even 40.6 is just fine. 40.5 or 40.6 is shallow WITHIN the ideal range.

When Garry says “Scores of 0-1 are often good for earrings and pendants" and "shallow stones", he is talking about really really shallow stones with 40.0 PA.

Fast forward to 3:30. That is a shallow stone. Notice the first stone at 3:23. That has 40.5 PA, which is considered ideal, not shallow.

 

[Phatkid77]

Is there anywhere you can pump numbers in like he’s doing for a rough idea of ideal scope image?! That’s cool

 

[Mlh]

Very helpful! Thank you!

 

[sledge]

Is there anywhere you can pump numbers in like he’s doing for a rough idea of ideal scope image?! That’s cool

Gotta have the software....$$$

 

[Garry H (Cut Nut)]

The software costs $325 and is worth at least $10k in the right hands.
The main reason HCA favors shallow diamonds is it is the only grading system in the known universe that grades spread rather than a straight rejection system (although GIA's rejection system is totally screwed up - hence 65% deep diamonds scoring Ex cut).
But I also believe that slightly shallower than Tolkowsky make brighter diamonds. Did a test with a new staff member yesterday with a very shallow and a H&A Tolkowsky and she picked the shallow as brighter.

 

[Phatkid77]

The software costs $325 and is worth at least $10k in the right hands.
The main reason HCA favors shallow diamonds is it is the only grading system in the known universe that grades spread rather than a straight rejection system (although GIA's rejection system is totally screwed up - hence 65% deep diamonds scoring Ex cut).
But I also believe that slightly shallower than Tolkowsky make brighter diamonds. Did a test with a new staff member yesterday with a very shallow and a H&A Tolkowsky and she picked the shallow as brighter.

Gotcha. Thanks. Guess I’m person I’ll find out soon!

 

[Garry H (Cut Nut)]

Gotcha. Thanks. Guess I’m person I’ll find out soon!
Can you do a test for us and come back and answer when you get the stone:
1. You and anyone else interested to look at the diamond - measure your close up focus distance with a ruler
2. when it comes see how close you need to be before it starts getting dark.
We should also have some idea of the viewing environments and what clothes color you are all wearing. Shaved small head or big boffy dark hair etc.

 

[Garry H (Cut Nut)]

Can you do a test for us and come back and answer when you get the stone:
1. You and anyone else interested to look at the diamond - measure your close up focus distance with a ruler
2. when it comes see how close you need to be before it starts getting dark.
We should also have some idea of the viewing environments and what clothes color you are all wearing. Shaved small head or big boffy dark hair etc.

 

[AV_]

how close you need to be before it starts getting dark

This is one thing that could be scored, if, one day, you could bring yourself to put even more time in the HCA. Then, it might come to thowing in minor facets - even more work that does not pay!

 

[Garry H (Cut Nut)]

This is one thing that could be scored, if, one day, you could bring yourself to put even more time in the HCA. Then, it might come to thowing in minor facets - even more work that does not pay!

How might the head obscuration be scored?
And yes, doing minor facets is a lot of work for no reward.
Currently we are working on Looks Like Size for any and all other diamond shapes though. this will not be a grading system per se, but it will enable a much better way to stop people cheating so much on fancy shapes.
Of course for any company wishing to take advantage of that will also need to supply or enter an .stl file - and making those available means we can do wonderful things to assess any diamonds beauty!

 

[flyingpig]

AGS and GIA: Persistent contrast is bad. Shallow diamonds look darker from "normal viewing distance". Lets punish all MRB diamonds with shallow pavilion less than 40.5 PA.

Garry Holloway : Persistent contrast is not necessarily bad. A diamond with shallow pavilion can be a reasonable option for earrings and pendents. In fact, shallow pavilion may contributes to bigger spread. Not all diamonds are used for rings.

I agree with @Garry H (Cut Nut) in this regard.

 

[diamondseeker2006]

@Garry H (Cut Nut) Would you please give me examples of numbers on what you think is a good pendant stone? I have never been totally clear on what you meant. So 40.6 PA or lower? What about the CA, table, and depth? Are 60/60 stones closer to what you mean?

 

[Garry H (Cut Nut)]

@Garry H (Cut Nut) Would you please give me examples of numbers on what you think is a good pendant stone? I have never been totally clear on what you meant. So 40.6 PA or lower? What about the CA, table, and depth? Are 60/60 stones closer to what you mean?

HI DS and all,
AGS apply 8 inches or 20cm as 'close inspection' distance. I think that is OK for young buying diamonds, but most diamond 'enjoyment' is experianced from around 14 plus inches +35cm.

Re the best pavilion angle - please stop using PA without reference to crown angle. You must remember the relationship between crown and pavilion angle - it is about 5:1. I did this 20 years ago:


Pretty much most diamonds with HCA scores under 1.0 will be better as pendant / E/R diamonds.
Diamonds that score Big under 1.0 or Bigger under say 1.5 are likely to be great pendant diamonds. GIA VG cut quality diamonds that score well on HCA are likely good too. Diamonds with larger table sizes and good HCA scores (maybe even over 61%) can appear really bright and in smaller earring and pendant diamonds this is an advantage.

But it can never be really a simple formula.

 

[AV_]

How might the head obscuration be scored?

I suspect that you could set a benchark for the 'dark' state of a shaded diamond, then vary the diameter of the relevant ASET area [to represent different viewing distances] until the given stone turns dark. I am not sure how these diastances are good or bad - I am fond of facets lookig like srads of mirror some of the time.

Currently we are working on Looks Like Size for any and all other diamond shapes though.

Measuring such impressions is too much for yours trully [I already have at least two metrics in mind & I am smiling into my coffee] Yet, I am intrigued by possible classifications calling cut diamonds one way or another after the impression they give - their pattern of reflections looks like a sort of 'colour' to me [color theory on the screen, as for light in painting] & would be very tempted to make the categories utterly not rankable, that's what prices are for thereafter.

I do not know if such a cavelier take makes sense, unless cut diamonds were comissioned like art is.

 

[Johnbt]

"AGS apply 8 inches or 20cm as 'close inspection' distance. I think that is OK for young buying diamonds, but most diamond 'enjoyment' is experianced from around 14 plus inches +35cm."

I suppose it's because we were 68 and 63 when we were engaged in April, 2018 and our friends are older with old eyesight, but the vast majority of people who have looked at the ring held it 20 to 24 inches away.

Sure, unscientific, but I guess they could see the 1.5 carat WF stone with an HCA of 1.0 just fine. IIRC, I tried it on the improved HCA once and got a 0.9.

My wife wanted a ring that would look good across the office, the room, the restaurant... or the mall for all I know. She's still very pleased with attention it gets.

 

[diamondseeker2006]

HI DS and all,
AGS apply 8 inches or 20cm as 'close inspection' distance. I think that is OK for young buying diamonds, but most diamond 'enjoyment' is experianced from around 14 plus inches +35cm.

Re the best pavilion angle - please stop using PA without reference to crown angle. You must remember the relationship between crown and pavilion angle - it is about 5:1. I did this 20 years ago:


Pretty much most diamonds with HCA scores under 1.0 will be better as pendant / E/R diamonds.
Diamonds that score Big under 1.0 or Bigger under say 1.5 are likely to be great pendant diamonds. GIA VG cut quality diamonds that score well on HCA are likely good too. Diamonds with larger table sizes and good HCA scores (maybe even over 61%) can appear really bright and in smaller earring and pendant diamonds this is an advantage.

But it can never be really a simple formula.

This is a post I will save and repost when this comes up! I sensed that a larger table might be better for earrings and pendants. I just didn't know what angles to look for. But now I understand how the HCA can be used to identify good prospects! Thanks so much, Garry!

 

[Mlh]

Which would be better for a ring... an hca score under 1 that signals big or bigger ? Not sure what the distinction is. Just looked up a super ideal out of curiosity. It came out .90 bigger. Thanks.

 

[mission1]

As I understand it, all other things being equal, Bigger in a sub 1 would tend to be shallower than Big and therefore may be darker close up. However, as is often said on the PS threads, HCA is a rejection tool and you can’t say which is the better diamond just from two low scores.

I compared a 0.5 score side-by-side with a 1.0 score......the arrows were *maybe* marginally darker close up in the 0.5, but I do mean maybe and marginal!

 

[Garry H (Cut Nut)]

This is a post I will save and repost when this comes up! I sensed that a larger table might be better for earrings and pendants. I just didn't know what angles to look for. But now I understand how the HCA can be used to identify good prospects! Thanks so much, Garry!

Thanks DS. Nice.
I would just add that once you get over say 70 points you dont want too large a table as you start to loose scintillation that is one of the 'messages' that says to folk - hey look at me!
For rings of say 1ct 54 to 59% is good.
For rings over 2ct keep it 58% or less.
For earrings and pendants I would add 1-2%.
But this is a feeling - not researched, so please don't take this as gospel elitism new rules

 

[Garry H (Cut Nut)]

I suspect that you could set a benchark for the 'dark' state of a shaded diamond, then vary the diameter of the relevant ASET area [to represent different viewing distances] until the given stone turns dark. I am not sure how these diastances are good or bad - I am fond of facets lookig like srads of mirror some of the time.

Apart from this topic http://www.diamond-cut.com.au/14_spread.htm which continues to favour shallower stones, the other 3 factors do waht you suggest by design AV.

 

[Garry H (Cut Nut)]

Measuring such impressions is too much for yours trully [I already have at least two metrics in mind & I am smiling into my coffee] Yet, I am intrigued by possible classifications calling cut diamonds one way or another after the impression they give - their pattern of reflections looks like a sort of 'colour' to me [color theory on the screen, as for light in painting] & would be very tempted to make the categories utterly not rankable, that's what prices are for thereafter.
I do not know if such a cavelier take makes sense, unless cut diamonds were comissioned like art is.

The market pricing is great for the informed, but first times have no idea that a radiant for example can spread 5% bigger than a round or 40% smaller.
As for art - Sergey and the Cut Group have an unrequited plan to hold a diamond cut competition. We had hoped a decade ago to get support from the Indian gem and jewellery association but the leadership changed.
India would be the perfect place to start something like this as there are so many engineers etc involved in planning the cutting of each piece of rough diamond. They could moonlight or work from within their company.