Holloway Cut Advisor "Outdated?"

[RockAndRoll2006]

Hey all. Just checking in, has anyone gotten feedback before that the holloway cut advisor is "outdated," and thus to be cautious when using it? I went to a jeweler (who otherwise seemed quite fair and reasonable) and he encouraged me to use the HCA, but stated that I "things have changed slightly" in grading and what proportions produces greatest fire, light return, and scintillation.

So my question is, has anyone else heard similar or was this guy putting on a show?

 

[SirGuy]

I'm sure someone much more knowledgeable and articulate (like Lorelei or Gypsy among others) will chime in shortly. But I think a main hiccup people have with it is that they use it as a selection tool rather than for exclusion. I think it's more beneficial to use it to say, "These three out of eight were under 2.0, so I'll look at them more closely and ask for IS and such," as opposed to saying, "This one is 0.8 and this one is 0.6, is the latter better?"

AGS Labs has a stricter cutting criteria for grading than GIA; the HCA isn't necessary when looking at those stones graded that way.

At the end of the day, when people discuss images and reports, not much is better than good old Mark 1 eyeball to know how a stone performs in real light.

 

[oldminer]

The HCA is a creation from several years ago when fewer diamonds were well cut for light return and consumers needed a screening tool or a selection tool to help them make a decision. Today we have AGSL and GIA making documents which give consumers a very good screening or selection tool for choosing a diamond. It all depends how picky you are as to whether you are screening further or selecting rather quickly. You can use such reports for extensive screening or you can use them as a rather friendly shortcut to buying a diamond rapidly with reasonable confidence that it will look very pretty and not be subject to any important criticism by family, friends, or even expert jewelers. The HCA gives users an insight into a diamond by creating a numerical score. This is something which the major labs don't currently do. Using the numerical result along with using the most respected reports is a great combination.

 

[metatrix]

Re: Holloway Cut Advisor "Outdated?"

These are the main criticisms I have read about the HCA:

It penalizes steep/deep combos too strictly (i.e. penalizes leakage under the table so slight that it can not be noticed by the human eye); while being too lax on shallow/shallow combos. This may be because:
A) the main philosophy behind the HCA is to heavily penalize steep/deep diamonds that have poor spread and too much leakage despite scoring Ex by GIA standards. This is a significant proportion of diamonds on the market, because it is the best way to preserve carat weight while still getting a GIA Ex cut grade on the certificate (thereby maximizing profit).

B) shallow/shallow diamonds suffer from poor light return, but at least they have excellent spread. This is a trade-off that may be worthwhile for consumers on a tight budget who want a large diamond. Whereas a steep/deep diamond has both leakage and poor spread, so it has no advantage.

The HCA also puts too much emphasis on spread. Almost every diamond you plug into the tool will give a vg or lower on spread. This is mainly because it is so incredibly hard to find diamonds with thin to medium girdles. So perhaps it is not realistic to expect such a high spread given what's actually available on the market.

Finally, because the HCA only evaluates the major facets (and only the averages of those), it fails to pick up on painting and digging. A diamond can be an AGS 0 in proportions and still perform poorly due to painting of the upper girdles. That being said, you cannot design something as simple as the HCA tool that recognizes girdle indexing. You typically need a full sarin or helium report or an ASET image to recognize that. This fault lies with the labs for not providing a girdle profile or commenting on girdle indexing on their reports.

Personally I like the HCA tool but largely ignore the spread component of it. Instead of plugging numbers into the tool blindly and just deciding based on the score, I reverse engineered the HCA tool
using trig and excel while assuming a thin girdle, and used what I learned from that process to create a list of acceptable crown/pavilion/table combos that also falls within GIA EX and AGS 0 proportions. I ignore depth % and judge the cut of a diamond based solely on the table/crown angle/pavilion combination. Then after screening for predicted optical performance based on that, I narrow down the remaining choices based on spread and the ASET. But I ignore the spread/girdle thickness/culet/depth % when I purely evaluating the cut of a diamond. IMO, spread should be part of the value determination rather than an independent factor in the cut evaluation.

 

[Lorelei]

I'm sure someone much more knowledgeable and articulate (like Lorelei or Gypsy among others) will chime in shortly. But I think a main hiccup people have with it is that they use it as a selection tool rather than for exclusion. I think it's more beneficial to use it to say, "These three out of eight were under 2.0, so I'll look at them more closely and ask for IS and such," as opposed to saying, "This one is 0.8 and this one is 0.6, is the latter better?"

AGS Labs has a stricter cutting criteria for grading than GIA; the HCA isn't necessary when looking at those stones graded that way.

At the end of the day, when people discuss images and reports, not much is better than good old Mark 1 eyeball to know how a stone performs in real light.

by Oldminer » 15 Jun 2014 11:20

The HCA is a creation from several years ago when fewer diamonds were well cut for light return and consumers needed a screening tool or a selection tool to help them make a decision. Today we have AGSL and GIA making documents which give consumers a very good screening or selection tool for choosing a diamond. It all depends how picky you are as to whether you are screening further or selecting rather quickly. You can use such reports for extensive screening or you can use them as a rather friendly shortcut to buying a diamond rapidly with reasonable confidence that it will look very pretty and not be subject to any important criticism by family, friends, or even expert jewelers. The HCA gives users an insight into a diamond by creating a numerical score. This is something which the major labs don't currently do. Using the numerical result along with using the most respected reports is a great combination.

Hi Sirguy and welcome by the way!

Thanks for your compliment, I think for me the issue is as you mention, I am still seeing consumers use the HCA for selection, not rejection and still there seems to be a belief that a lower score is better, this is something that has been going on for years and is an understandable misconception. Yes as Metatrix mentions, the HCA does penalize steep deep combos, will also ding for steep pavilion angles but I believe this is actually justified in warning the consumer that images with certain proportion combos are essential in order to know how much of an issue, if any, a steep/ deep or shallow/shallow stone has. There might not be an issue at all with some of these proportion combos but all the HCA is doing is alerting the consumer there might be one and emphasizes that final selection should be done with images and buyer preference etc. There are other aspects that the HCA cannot detect such as painting and digging, however it depends on the particular consumer whether this is going to be something they even want to consider when buying a diamond but for those that want to go in depth, ASET is probably the best tool to use but with the top branded stones cut for visual balance, it's not going to be an issue anyway.

But perhaps for the point of this post, I am digressing a bit too much, my opinion is when used in the right way as a first round rejection tool, the HCA is very useful especially for novice consumers. As Oldminer mentions, when used in the right way, the HCA does give a buyer reasonable confidence that the diamond in question has a good chance of being a pretty stone and worth further evaluation and that's an excellent thing.

 

[teobdl]

metatrix doing it like a boss.

I won't comment too much Garry's preference for shallow stones, but I will say that he has also discussed the differential effects of dirt on steep crowns vs shallow crowns. This and probably other factors go into this preference.

I don't know how spread factors into the HCA score algorithm. But I agree that it may be more helpful to remove spread from the HCA itself and given separately as a weight-spread metric (e.g. " your 0.9 ct diamond has the spread of a tolk ideal 0.75 ct diamond) and let the consumer make a decision as a separate value question. HCA score should be given on basis of PA/CA/T% and possibly LGF % (+star%?) if it doesn't make it too complex (or if it's even useful w/ GIA's rounding).

 

[diamondseeker2006]

Most ideal cut stones get VG for spread on the HCA. So as long as you go into it knowing that, it just isn't a problem. I certainly am not going to pay for a .90 ct diamond that has the diameter of a .75 nor would I pay for a 1 ct diamond that had the diameter of a .90. There are better cut diamonds out there so why settle??? I like excellent on the other three measures,though.

metatrix..I think thin-medium girdles are plentiful. Are you saying that you think they are hard to find in GIA Ex or AGS 0 stones?

I hope people realize that the HCA is not used at all on AGS ideal cut stones since they are basically pre-screened to have optimal light performance. With those, I like to see the magnified stone image and the idealscope image (and hearts image if available).

We use the HCA to narrow down GIA excellent stones. Many of us consider up to 2.5 or so on the HCA subject to seeing the idealscope image. I had a 35 ca, 41 pa stone that had an excellent idealscope image in spite of having higher than 2 on the HCA.

 

[metatrix]

Re: Holloway Cut Advisor "Outdated?"

What I would like to see incorporated into the tool (as a separate score perhaps) is the size of the table reflection (calculated based on table % and pavilion angle). The size of the table reflection increases with a steeper pavilion angle and with a larger table. If you have both a big table and a steep pavilion you could end up with a massive, unsightly table reflection. This is especially problematic in a large diamond or in a diamond with poor optical symmetry.

I did not know that light performance when the diamond is dirty played a factor in the HCA's preference for shallow/shallow diamonds. That's very interesting and cool because how your diamond performs when it is grimy is such an important practical consideration yet almost nobody pays attention to it when buying. It would be neat if the HCA tool gave a score for how much the optical performance deteriorates as the diamond accumulates skin oils on the surface.

As far as incorporating lower girdle length and star length, I think the best way to do that is for the tool to simply give a verbal statement (with diagrams for illustration) regarding the optical character of the diamond (i.e. pin flash vs broad flash). It's a matter of personal preference after all.

A small star % in combination with a large range in girdle thickness usually makes me suspicious of painted girdles, especially in AGS stones without an ASET image. Another reason to ask for an IS and/or ASET image before you buy.

 

[Karl_K]

I hope people realize that the HCA is not used at all on AGS ideal cut stones since they are basically pre-screened to have optimal light performance. With those, I like to see the magnified stone image and the idealscope image (and hearts image if available).

I use it on AGS0 diamonds every time I look at a report.
Well sorta, I have doing this for so long that I can look at the cp angles and table% for most combinations and know what the hca will say. For less common combos I do run the hca itself on them.
The ags system is not perfect and the hca serves as a check and balance.

The hca is best at telling you if the crown pavilion angles compliment each other, that is fundamental, if they don't the diamond will not work without a compromise such as painting or digging which impacts scintillation to a large degree.

It does have its limits, shallow stones for pendants and ear rings get good scores, it is overly harsh on 41 degree pavilions.
It does not consider all the facets but that is fine because it is not a selection tool.
Properly used and applied it is still a good tool that answers a fundamental question about a diamonds potential.

 

[metatrix]

Re: Holloway Cut Advisor "Outdated?"

I think the most important thing about using the HCA is understanding what is behind the score. You need to understand the relationships between crown angle, pavilion angle, and table. If you understand how those three measures interrelate to affect light performance and why, then there is very little mystery to the HCA tool. Instead of focusing so much on the actual numerical score, you should pick the combo of angles and table that gives you the look and spread that you are after, based on your priorities and preferences (i.e. the inescapable trade off between brightness, contrast pattern, fire, and spread).

My personal ideal is a 40.8 pavilion with something like a 34 crown angle and 56 table, for a good balance between brightness and fire. Then for minor facets I like a 75% girdles and 55% stars because I like fat arrows, lots of contrast, broad flashes of fire, a concave table, and a small table reflection. And I like classic girdles with no painting, because I like a consistent, crisp contrast pattern around the girdle. Even slightly painted girdles mess with the contrast around the arrow heads. Oh, and a thin girdle for max spread!

 

[Texas Leaguer]

Like Karl and others have said, HCA is still a good tool if used appropriately and if the limitations are understood. I think one thing that gives rise to the "outdated" question are statements such as these on the results page of the tool itself:

Even though HCA grades cut more effectively than systems like the AGS, it does not yet factor in symmetry and minor facets.

This statement was most probably written before the AGS Light Performance grading system was released in 2005.

Also on the results page is this statement that seems to imply that the tool has not been updated in over a decade.

HCA scores were adjusted Dec. 15, 2001 and Feb. 6, 2003.

It would probably be beneficial for Garry to update the messaging on the tool.

As Dave Atlas suggested, when HCA was first introduced, it was an innovative tool that was indespensable for getting a handle on cut quality. Things have changed alot since then, making it much less relevant if advanced information is available on a given diamond.

 

[RockAndRoll2006]

Thank you all for the reply! Looks like all have very similar opinions, which I will take into consideration as I go about using the HCA!

 

[Gypsy]

This isn't the first time I've seen this posted. There appears to be a vendor that says this to most people.

I don't have anything to add to what's already been posted, personally.

But here is this information John Pollard has posted in the past, that I find helpful.

HCA usage warnings here: https://www.pricescope.com/wiki/diamonds/holloway-cut-advisor

In Context

Just imagine that you're trying to get to know someone's looks and personality...

An HCA score is merely like having a chalk outline of the person.
Grading report numbers are like having the person's height, weight and clothing measurements.
An ASET or Ideal-Scope (for RB) image is like having a still photo of the person.
An AGS Platinum "0" in performance is like a panel of judges confirming that the person's personality and looks are solid.
A 3D scan in sophisticated cut-calculation software is like having a video interview with the person.

Eventually, it's a lot of great information. All told it's enough for an experienced cut-specialist to make very detailed performance predictions. But in the end, a live date (dinner & a movie?) will be how you finally judge total personality and looks as you, individually, perceive them.

 

[TC1987]

The HCA is a creation from several years ago when fewer diamonds were well cut for light return and consumers needed a screening tool or a selection tool to help them make a decision. Today we have AGSL and GIA ...

True, but many "outdated" diamonds from the dark ages are still out there, in pawn shops, at estate sales, on Craigslist, so the HCA is still useful and still needed. Pricescope deals mainly with some elite fraction of the diamonds available for sale. But many of the Fair / Good / Poor cuts and the ones with EGL reports are still out there for sale elsewhere.

 

[OoohShiny]

This isn't the first time I've seen this posted. There appears to be a vendor that says this to most people.

I don't have anything to add to what's already been posted, personally.

But here is this information John Pollard has posted in the past, that I find helpful.

HCA usage warnings here: https://www.pricescope.com/wiki/diamonds/holloway-cut-advisor

In Context

Just imagine that you're trying to get to know someone's looks and personality...

An HCA score is merely like having a chalk outline of the person.
Grading report numbers are like having the person's height, weight and clothing measurements.
An ASET or Ideal-Scope (for RB) image is like having a still photo of the person.
An AGS Platinum "0" in performance is like a panel of judges confirming that the person's personality and looks are solid.
A 3D scan in sophisticated cut-calculation software is like having a video interview with the person.

Eventually, it's a lot of great information. All told it's enough for an experienced cut-specialist to make very detailed performance predictions. But in the end, a live date (dinner & a movie?) will be how you finally judge total personality and looks as you, individually, perceive them.

Great info, thanks very much

 

[MrsT]

Re: Holloway Cut Advisor

[quote="metatrix|1402857132|3693705"

I did not know that light performance when the diamond is dirty played a factor in the HCA's preference for shallow/shallow diamonds. That's very interesting and cool because how your diamond performs when it is grimy is such an important practical consideration yet almost nobody pays attention to it when buying. It would be neat if the HCA tool gave a score for how much the optical performance deteriorates as the diamond accumulates skin oils on the surface.[/quote]

I'm trying to purchase a new diamond and one of the issues I have with my existing stone is it is always dirty around the edges. My stone must be cleaned daily and the edges always look cloudy. This is on an AGS ideal signature cut. Can you enlighten me regarding this issue and what makes one diamond do better with grime over another?