Questions about the hca

[strmrdr]

As per request:

Light conditions:
What light conditions does the hca predict performance under?
B-scope – direct
Isee2 – indirect
Hca - ?
Ideal-scope - ?

Garbage in Garbage out:
Lets say for this part of the discussion that the hca does everything it is billed as doing and is 100% accurate.
There are several examples on the board of 3 different sarin machines giving widely different results with the resulting hca scores ranging from under 2 to over 3 depending on which numbers are used.
While there isn’t much you can do about this on the hca level how would you address someone who bought based on hca scores then gets another sarin done and it came out with a less than great hca score?

Range:
Under 2 is considered great but another 1 point jump to 3 is considered not very good at all. What is the explanation for this?

How it works:
While you have dropped hints here and there but I don’t recall seeing a full discussion on what it does and why it does it that way.
That’s one thing that bugs me about it is that it is too magic boxish with trust me for an explanation.


Peer review:
All we ever really read other than here is how widely inaccurate it is can you point us to an independent study that looks into the hca?

There are a couple more but I know you are a busy person so I will leave off here for now.

 

[aljdewey]

Lets say for this part of the discussion that the hca does everything it is billed as doing and is 100% accurate.

Let's not start with that assumption....simply becuase nothing can truly be 100% accurate, nor does the HCA claim to be. It may disqualify stones that perform well, and it may give great scores to stones that end up being duds. It's not meant to be a definitive tool....it's meant to help weed out stones that aren't *likely* to perform well.

While there isn’t much you can do about this (variations in Sarin data) on the hca level how would you address someone who bought based on hca scores then gets another sarin done and it came out with a less than great hca score?

I would address that person by asking why they would do such a thing (buy based strictly on hca scores) when that's not how it's intended to be used? It's not offered as a "selection" tool, it's meant as an elimination tool. That means that it should be used *only* to narrow down the wide field of available stones to a few. It's also expected that you will subject your final contenders to *other* tools/scrutiny in making your final selection. Buying based only off the HCA score is like trying to build a mansion with only a phillips screwdriver.....not enough tools.

Under 2 is considered great but another 1 point jump to 3 is considered not very good at all. What is the explanation for this?

Garry would be the best person to offer explanation here, but I'd respectfully observe that there are SEVERAL increments between 2 and 3.....such as 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9.

All we ever really read other than here is how widely inaccurate it is can you point us to an independent study that looks into the hca?

Most people don't even know what the HCA is. The only dissenters I'm aware of are a handful of folks from the "other network", and they are balanced by a handful of folks here who believe it does offer some meaningful input.

 

[strmrdr]

AL interesting answers :}
Gary laid down a challenge that if someone asked some questions he would answer them in the poll thread so these were really intended for him but I figured I wouldnt specify that bacause it might get some interesting replies:}
Which happened thank you :}

just one comment:
Thanks for confirming my point on the last one about what we hear about the hca.
Your right of course but the question of an independant study still needs an answer :}

 

[Garry H (Cut Nut)]

OK Storm, my first question for you is have you read www.diamond-cut.com.au ? I have been very open there and also on the patent application about how and what and why.

It seems from most of your questions that you either have not, or did not take much of it in.

Please do that first then ask the questions (if any) that remain and I will gladly answer what I can.

As for measurement acuracy, the same applies to all the existing labs.
As for changes in grades that could come about from the Sarin data, this is also true for AGS, EGL, IGI, HRD for crown and pavilion data and for all labs for table size which is one of the least accurate measures (that is why they all round to the whole percentage). As you say GIGO, but at least the gigo is a hole lot better than what we had 15 years ago.

You will be pleased to know I am involved in devising better measruement systems. So is Dave Atlas with the ImaGem team.

Finally have you bothered to ask the same question for AGS 0 graded diamonds that will fall over that precipice of steep crown deep pavilion and get a lower grade when they bring out their new system?
HCA has nothing of the impact on price that AGS 0 has, and as everyone will tell you, HCA is a tool, it does not replace human eyes, it helps narrow the search.

Finally, where are all the great examples of HCA calling bad stones good? Surely that would be a bad thing, worse than calling good stones bad from the perspective of what I set out to achieve.

 

[strmrdr]

Gary,
I have checked out the website on more than one occasion the lighting question is answered there but how does that relate to real world lighting outside the jewlery store and scopes?


The peer review question I dont see an answer too.

I have read what has been released about the new measurement systems but they dont help today. So its still a problem. To be fair its a problem not just for the hca but the others as well.

No I have not talked to AGS and dont know who to talk to if I wanted too.

Im not the one that claimed that the hca called bad stones good Im trying to better understand the hca and where it stands.
I have an open mind about the hca, im just not satisfied that I know enough about it to put a ton of trust in it.

 

[nicknomo]

I am new to these boards, but it has taught me a lot.

The HCA makes a great deal of sense to me, maybe because I like to read about physics.. optics were never my strong point, but basically there are some things that can either reflect light or let it pass through, based on a very small change in angle of incident. The angles at which the crown and the pavillion are aligned will be the difference between a light beam being reflected at the crown, back at the crown from the pavillion, or passing right through the stone.

I'm sure some simple 3d modelling and ray tracing could provide some very interesting results, which would probably be the most accurate way to judge a diamond. The amount of light reflected back could very easily be judged based on the specs given by an AGS report... That at least can be purely mathematical... I'm not sure how the HCA works, but I would guess it's on the same principles.

I'm not sure how easy it would be to calculate fire and scintillation, but I would guess it would be a few degrees harder.

Beauty though is something different altogether. If you want maximum light return you buy a mirror. It seems really need a mixture of a lot of things for a diamond to truly be excellent.. Of course some people have different tastes, so any scale will never be absolute...

With all of that being said, this is IMO a very logical approach. Even your eyes can play tricks on you with the lighting in stores and such. It's a good reference at the least. You could probably weed out a lot of bad stones with this chart.

EDIT: I just want to add that of course it's not going to work 100% perfectly. The supplied values can only be approximations and it only uses a limited amount of information. I don't want to imply this should be the basis for a purchase decision. I do think that it is probably worth taking a look at, and something to consider... especially when you cannot see the stone.

 

[Garry H (Cut Nut)]

At the Moscow conference my peer's did not criticize HCA.
The only presentation directly one the topic was by Bruce Harding (aka Beryl here on Pricescope). He presented a brief paper on Slope parametric systems and praised HCA.

I attempted years ago to publish in Gems & Gemology, but I did not have the time for the to and fro. What would have been published is what i put on www.diamond-cut.com.au and the process you have gone through has happened many times here and on the other board.

Unlike Brillianscope and I-See2 etc who have been very secretive (they only released patent info) about how what and why, I have bared all

With regard lighting in real world - where i had populations of real diamonds with known proportions (mainly the better zones) I have shown hundreds of diamonds to my staff, suppliers and customers. I do this in a jewellry store with halogen spots on high light colored ceilings with some natural daylight, and also next to a large window in shaded daylight. If the daylight is inadequate and also in addition I use office fluoro strip lighting. These tests have been over many years (more than 10) but particularly around the 2000-2001 period. they were to test the Firescope / ideal-scope as much as they were to test the HCA. The fact that what I arrived at is also similar to what MSU, GIA WLR and new research from AGS and GIA is not because I am a rocket scientist, it is because it reflects the nature and physics of the problem.

That all said - I am happy with HCA?
No!

It is not a cut grading system, it should be used for seletion / rejection for closer inspection.

I have a plan to enlarge it to fancy shapes however, and improve its accuracy. That is a tickler

HCA's main use should astually be by cutters for planning the cutting of rough, and we have made a few steps in that direction

 

[Serg]

----------------
On 6/30/2004 12:17:41 AM nicknomo wrote:


Beauty though is something different altogether. If you want maximum light return you buy a mirror. It seems really need a mixture of a lot of things for a diamond to truly be excellent.. Of course some people have different tastes, so any scale will never be absolute...

----------------

Why does mirror make maximum light return?

 

[strmrdr]

Another question:
Assume that the measurements are spot on for this exercise.
Lets say I have a diamond with a 34.4-34.6 crown angle. average 34.5 with most of them being at 34.5 with one at 34.4 and one at 34.6.
60% depth
The paviallin is 1/2 at 41.2 and 1/2 at 40.7 with a 40.9 average.
Using the average it comes out as 1.4HCA.
But using the average for the crown and what 1/2 the pavilian is its a 3.1HCA
using the others its a 1.2HCA.
So over all what is the performance of this diamond?
Is it a 1.2 1.4 or a 3.1 or someplace in between?

No other information or scope pictures are availalbe is this a buy or pass?

 

[nicknomo]

Mirror's reflect almost all of the light that hits it from pracitcally every angle, that's how you see your reflection.

 

[nicknomo]

Well, that's just information you obviously can't know when you don't have the stone in front of you. Of course with limited data, you have to assume that the angular symmetry is very good, and their isn't a large difference.

It would be more likely that a stone with ideal/excellent symmetry would have proportional angles. There is certainly less of a possibility that if the stone's size proportions were not symmetrical. Of course there are plenty of ways the angles can still have a sizeable percentage difference with ideal symmetry.

But there are obviously a lot of other factors, including how the facets are cut. However, there is no way you can really judge that... You would need an exorbitant amount of information before you can classify a stone based on anything more.

I really think the next step is 3d imaging.... If you can get an accurate 3d mockup of the diamond, you'd have an amazing way to grade the cut.... It would just be difficult to find a way to get an exact 3d model of the diamond that doesn't cost a fortune.

 

[Paul-Antwerp]

Storm,

That is exactly why the HCA is a sorting/elimination tool, and not a decision-making tool.

The HCA works with limited data and averages, and presumes the best possible for the non-entered or non-available information. Like you say, one can have great average angles with a lot of deviation. The HCA-score will be based on a symmetrical stone.

Now, you can definitely have a mediocre stone with great average angles, you cannot have a great performer with bad average angles. So, the HCA weeds out the bad performers.

Therefore, a high HCA-score gives you a higher chance of getting a great performer, but no certainty. One should also check other tools and of course look at the stone itself.

We should however take care that the success of the HCA does not bring about abuse. One could imagine dealers starting to offer asymmetrical stones with great HCA-scores at unbeatable prices, since these are in fact not good performers. Not the fault of the HCA, but of the people using it.

Live long,

 

[Serg]

----------------
On 6/30/2004 3:09:50 PM nicknomo wrote:

Mirror's reflect almost all of the light that hits it from pracitcally every angle, that's how you see your reflection.----------------

This statement is same for 90 degree prism.
But 90 degree prism has bad LR.

Is direction for LR important?

If we speak about spot light I think small mirror has very bad LR to eye.

 

[strmrdr]

----------------
On 6/30/2004 3:09:50 PM nicknomo wrote:

Mirror's reflect almost all of the light that hits it from pracitcally every angle, that's how you see your reflection.----------------

Not true.
a flat mirror has rather large loses for light that hits it at an angle and not all mirrors are as good as others.

Perrform this experment:
Take a mirror and a flashlight and put the mirror in a darkened room and surround it on 3 sides by white posterboard.
Now shine the flashlight into the mirror at various angles and note the light return on the posterboard.
A highly direction and bright flashlight works best for this.

Flat mirrors have a very narrow range of angles that they return the max amount of light at.


Another experment shine a real bright light at a mirror from 3 feet away. A 250W or better flood is good.
Monitor the temperature of the mirror but dont burn yourself and wear sun glasses.

 

[nicknomo]

To both strmrdr and serg:

I think we are knit picking here. I have a 10" dobsonian reflector, which will reflect the faintest light source back when the angle of incident is roughly 90 degrees perpendicular.

If you are implying that your kmart wall mirror will not reflect as much light as my dobs, then duh.

It is a basic principle that an ideal mirror will reflect light off of it's surface at the complementary angle.

If you want to challenge my statement about angles, once again I think you then fail to see the obvious. A good mirror will reflect light even at a steep angle. Of course the amount of light reflecting the mirror will always be less then what is returned, and this is usually due to the graining or "size of the bumps" on the mirror. Unless your angle of incident is very small angle, on a fine grain mirror you will get a miniscule amount of light loss. Mirrors don't necessarily have to be made out of glass either. They can technically be made out of anything. Anything moderately reflective can be classified a mirror. Hence, the most light return you are going to get will always come from a mirror... unless there is something obscure that I don't know about.

Besides, it was a joke. I guess it was a bit too complicated to be funny to anyone other than me.

 

[Serg]

----------------
On 7/2/2004 11:29:48 PM nicknomo wrote:

To both strmrdr and serg:



Besides, it was a joke. I guess it was a bit too complicated to be funny to anyone other than me. ----------------

Nicknomo,

My and strmrdr statements are quite different.

My statements: "6mm perfect round mirror has worse LR to eye than 6mm good round diamond."
It is not joke.

But "6mm perfect round mirror has better GIALR than any good 6mm round diamond."

Do you agree It is important point for discussion?

 

[nicknomo]

Serg,

I'm sorry if I confused your statements. It was late and I didn't make a distinction.

Anyways, I meant MY statement was a joke.

As for a round mirror vs a round diamond, everything except the light hitting a table would be reflected away. I would think that the number of photons reflected by that small table area on an ideal mirror might still be more than all of those from the entire diamond. Of course, I see what you are trying to say.

I think though you misunderstood my statement,though. I wasn't thinking of a mirror with a round brilliant cut. I was thinking, just a mirror. The type that is intended to reflect light back at you.

You see a 6mm half circle hollowed out mirror to exact & perfect proportions would send back much more light than a diamond ever could. If you put such a mirror in direct sunlight, it would burn a hole through your eye at the right focal length.

You see, this is how you know you've made a bad joke

. What I was saying was that light return isn't the only aspect of beauty when it comes to diamonds. If you want something that will reflect the most light back at you, you can find a mirror that does an amazing job at that. Of course that doesn't look "pretty", it's not eye captivating, and for lack of better words its boring.

I'm sure you probably realize this, so once again any joke that requires explaining is a bad one. I don't mean this in a derrogatory sense, as I'm not insinuating it has anything to do with your intellect... rather just my delivery.

Have a good one,
Nick

 

[Serg]

----------------
On 7/3/2004 12:29:08 PM nicknomo wrote:

Serg,


I think though you misunderstood my statement,though. I wasn't thinking of a mirror with a round brilliant cut. I was thinking, just a mirror. The type that is intended to reflect light back at you.

You see a 6mm half circle hollowed out mirror to exact & perfect proportions would send back much more light than a diamond ever could. If you put such a mirror in direct sunlight, it would burn a hole through your eye at the right focal length.


Have a good one,
Nick

----------------

Nick,

I sure I understood your statement correctly. I speak about simple mirror too.

I think to catch the sun accidentally by diamond much more easy than by 6mm mirror.
Do you agree?
It is not attack to you.
It is attack to standard simplification about 100% LR and maximum LR by mirror. Many people use similar "joke-simplification".
May be I am fighting with windmills .

 

[nicknomo]

Serg,

Well when you say accidentally what do you mean? With an ideal mirror, light will simply return from the surface at an angle complimentary to angle of incident. This is very different from a diamond which has a much more complicated system for the light path. A mirrored shape diamond could never have such an effect, if this is what you are implying. A mirror can't catch light at all. When you have a bad mirror, it will simply diffuse the light, but this will not produce anything close to the same effect.

It's an apples oranges comparison really.

I don't think you will be able to get me to budge on the light return though. The light on a mirror is very well preserved in angle, frequency and amplitude. A 6mm perfectly crafted concaved mirror (which would be very hard to make btw) will be glaring white in sunlight. Of course, when you angle the mirror away you would see the dull sides of the mirror... Does this mean it has bad light return? No, it just means it isn't partially transparent. If it was transparent, then immediately you are losing light. However, this is the appeal of a diamond. This is why people pay $10,000 for a diamond, instead of getting a a 20$ piece of pyrex.

Light going into the diamond is allowed to pass through, while also being reflected, refracted while producing a sparkling and beautiful effect. Of course you want good light return on a diamond, otherwise it will be dull. However, if it had 100% light return it would probably be worth as much as the pyrex.

Either way, charge on Don Quixote.

 

[Serg]

Nick,
What is LR for you.
1)Is it light going out from diamond?
Or
2) Is it light going to your eye.

If first, Mirror has 100% LR.
If second Diamond has better LR than mirror

 

[nicknomo]

Well, I am talking about a little of both. In regards to light return to the eye, I am comparing the two at their optimum anngles between light source,mirror and the eye. I've mentioned in the previous posts how the mirror is limited in how it reflects light back. Basically, light return from the mirror

I was comparing the two positioned "face up" with the light source being similarly angled to the persons line of sight.


Of course this is only if we are talking about a perpendicular angle of incident. Otherwise the light return to the eye could potentially be worse, since the mirror would perfectly reflect the light at the proper angle, which under many circumstances wouldn't be at a persons eye. As I've said, a mirror works in a very simple manner... and I do think that a diamond can "capture light" from many more angles for obvious reasons. I've stated this from other posts.

If you have a high degree of ambient light, or multple light sources (i.e. lots of flourescent ceiling lights), then your odds of getting a lot of light exiting the mirror towards the eye would be very good.

However that is getting overly complicated. Light is reflected very well from the mirror, and can be angled so that light from any light source will hit the eye brighter than a diamond can (no matter which way you angle it).

 

[Garry H (Cut Nut)]

Unfortunately nick it is nowhere near that simple.
for instance:
The higher light return from a mirror pointed directly at a light may cause an intensity that is more than the threshold of the eye to be an advantage. Further more the facets of the diamond may take light from many sources and no light from non light sources and create a patchwork that, with only a small part of the light return, can be more bright to our eyes (remember we have 2 of them) where as the mirro is likely to only shine the light in one eye.

It can get very complex.

 

[nicknomo]

The higher light return from a mirror pointed directly at a light may cause an intensity that is more than the threshold of the eye to be an advantage.

Yes, clearly so. I've never stated that a mirror was nice to look at, especially if it's reflecting light from the sun.

Further more the facets of the diamond may take light from many sources and no light from non light sources and create a patchwork that, with only a small part of the light return, can be more bright to our eyes (remember we have 2 of them) where as the mirro is likely to only shine the light in one eye.

It can get very complex.

Well yes it can get very complex, even with mirrors. A hallowed out oval or half circle mirror could potentially be made to deliver light to both eyes, but then you would be constricting where a light source can be in order to get a reflection.

I really don't know why such a big fuss was made over my joke. Who would ever do something as silly as wearing a mirror on their ring finger?

The truth is though, that a mirror has the potential to return light in a manner far superior to any diamond. If you wanted to go outside and blind yourself with glaring white light, then a mirror would be your best choice. That was the joke I made, and it is silly but true. I'm a little baffled by everyone's need to try and combat this fact.