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HCA Questions

Discussion in 'RockyTalky' started by headlight, Aug 14, 2019.

  1. headlight
    Brilliant_Rock

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    by headlight » Aug 14, 2019
    Hello PSers!
    So HCA <2 is an acceptable score (and then go from there for assessment) - understood.

    My question then becomes, wouldn't the particular rating for each category of the HCA matter/make a difference in the stone's performance?

    For example, say a stone gets a score <2... yet for what I call the 3 performance categories (Light Return, Fire, Scintillation), doesn't it make a different what those individual scores are?... hence what actually COMPRISES the total acceptable score?... i.e., is it better to get Excellent for a particular category than Very Good? Does that make a difference?

    As example, I have posted the HCA for my stone (as that's the only thing I have to go by as comparison when I see detailed HCA scores referenced for various potential stones in question on this Forum), of which you can see my diamond's HCA is 1.6 (which I was ecstatic about as I had been off this Forum for quite some time prior to getting this diamond and it didn't occur to me to run it through the HCA until after it was purchased, after I returned to participating here, so I definitely lucked out on my HCA!).

    So my stone got Excellent for what I call the "performance" categories. It only received a Good for spread because it is a deeper cut stone (per PS standards... still made GIA 3X but that's a topic I will bring up in another thread lol!). Anyhow, it only received a Good due to its depth.

    I don't know if it is safe to assume that had the depth been better, it would have scored higher for Spread and my total HCA score would've been even lower than 1.6?... I know each spec has an influence on score but given depth is included in providing a score the fact that my diamond's deep(er) depth played a factor in the score, had the depth been better it would've changed the score in a positive way??

    So for my diamond, as example, is it a good thing that what I refer to as the performance categories all received Excellent... or does it not make a difference what the individual scores are as long as the HCA is <2? As comparison, take a stone which has a better (lesser) depth than mine... it would get higher than Good for Spread... and let's say that stone ALSO received an HCA of 1.6... that means it got lower in one/more of the performance categories than my diamond... so does that mean as far as PERFORMANCE (or potential performance) goes, my diamond would fair a little better overall???

    I realize that Spread IS a "performance" factor in a diamond for many/most people (it wasn't for me but that's another story)... but putting a stone's visual size to its actual carat weight aside, where we are just looking at how the diamond performs (or potential performance) hence as to concerning ourselves with its Light Return, Fire, and Scintillation, does that make a difference in whether it gets Excellent, Very Good, Good, or Fair... as long as the HCA calculates as <2?

    OR does it not matter how the score gets to be <2... if it does, great, and then you go by ASET as to making a performance determination???

    Do we know if, IRL, a stone that received an Excellent for Fire, as example, performs better than a stone that received a Very Good, etc?

    This Forum's "mission", as it appears to me, is to assist buyers in sourcing stones of the highest quality and performance, and in the process embraces the use of the HCA as the first step, as a rejection tool. Why then is there negativity toward it from some? Even Mr. Holloway, himself, says it is a rejection tool... he isn't claiming it is the be all, end all, but that it is a useful tool for which to begin the process of weeding out diamonds as the "hunt" narrows toward the best option for a particular buyer based on their goal(s). So why the criticism? There are "a million" stones out there, one has to have a place to start the process!

    Moving on to more questions, I have attached my stones specs and the additional HCA info. On the image that shows the graph of possible cut grades, it appears in the "sweet spot" for both GIA3X as well as AGS0. We all know that due to my diamond's depth, my stone is no way an AGS0! So how can it plot as such?

    Also, in the image for "Looks Like Size", it says it looks the usual size for its carat weight, but we know it doesn't as my 2.01 carat diamond has measurement of 8.01x8.06x5.06. I realize this is still the Beta version of this addition to the HCA. However, when you go to the description of what each Spread means (attached), it does state that it may be a bit smaller due to slightly thicker girdle and/or small table (both of which my stone has), so that is the more accurate assessment.

    I have included my diamond's info as points of reference because, as I stated earlier, that is the only thing I have to use as comparison in learning how all this works as I see the potential diamonds submitted for review by buyers. IMG_2795.png IMG_2798.png IMG_2800.png

    Thanks for reading and thanks, in advance, for your input. Much appreciated! ~ Headlight
     
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  2. OoohShiny
    Ideal_Rock

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    by OoohShiny » Aug 14, 2019
    It's too late for me to think :( :lol: so I'm going to be ultra-lazy and page the man @Garry H (Cut Nut) himself, if that would be ok! :)
     
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  3. sledge
    Ideal_Rock

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    by sledge » Aug 14, 2019
    I'm sure Garry will be here soon to give a much more detailed & better explanation. But in short, the HCA is an easy way to analyze diamond proportions and get a feel if you are in the ballpark or not. Remember, the data we see on the cert is already slightly manipulated (8 actual crowns & 8 pavilions that gets rounded & averaged so we see just 1 value on the cert). Then the HCA makes assumptions, etc on top of that.

    It does a good job, but it can't catch everything. It also doesn't require every buyer to "nerd out" on diamond data.

    I'm running short on time, but I responded earlier with some information you may find interesting. Stone gets a wonderful 1.5 HCA score, but performance images show leakage.

     
  4. yssie
    Super_Ideal_Rock

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    by yssie » Aug 14, 2019
    @headlight Are you familiar with Myers Briggs?

    The HCA is a lot like it, only it’s aiming to assess and characterize diamond personality rather than human personality.

    I just landed and need to get to my hotel. But I understand what you’re asking, and I appreciate that you’re questioning the bigger picture rather than settling for losing yourself in the weeds. I’ll elaborate on my own thoughts tonight.
     
    


    


  5. headlight
    Brilliant_Rock

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    by headlight » Aug 14, 2019
    Thanks so much for all this!
    It’s interesting you referenced the CA/PA of the 35/40.8 because I saw this concern referenced on a thread the other day and it caught my eye given it’s my diamond’s stats, as well, because just last night I was doing some “investigative work” lol and came across an AGS0 stone that had the same CA/PA (i.e., apparently that combo does work in some instances!).
     
  6. headlight
    Brilliant_Rock

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    by headlight » Aug 14, 2019
    Thank you!... I will look that up!
     
  7. HDer
    Brilliant_Rock

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    by HDer » Aug 14, 2019
    Mind if I add a question to this thread? I noticed now that there's a h&a checkbox. Checking it will lower some diamond's HCA by a few tenths. Any reason why?
     
  8. headlight
    Brilliant_Rock

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    by headlight » Aug 14, 2019
    Great question... I would think that a score would be penalized for NOT being H&A (as mine is not H&A).
     
  9. yssie
    Super_Ideal_Rock

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    by yssie » Aug 15, 2019 at 12:18 AM
    Okay, I'm settled! Time for tea and some eleventh hour musings ::)

    Here's a summary of the Myers Briggs personality assessment:
    http://www.humanmetrics.com/personality/type

    The very short version is that there are four 'categories', and your answers to various questions ("how would you react to X", "do you prefer A or B", etc.) determine how strongly you associate with one end of the spectrum or the other within each of those four 'categories'. Each 'category' is a scale - you can be extremely extroverted, extremely introverted, or somewhere closer to the middle. Taking the assessment yields four letters that represent your dominant traits; most versions also tell you how extreme your results are in each 'category'.

    I went to a Catholic high school. Our religion teacher had us all take this Myers Briggs test at the beginning of our final year. Most of us scored similarly to our friends. Near the end of class our teacher asked us what the best score was... the best score, it turns out, is to have no score at all. To be right smack in the middle of the scale in all four 'categories'. Perfectly balanced, just as Jesus was (religion class!). The worst score? Well, we all agreed that a little skew makes us human. Actually, we all agreed that a little skew adds variety and to a group, which makes us all more interesting... but extreme skew in any category (or categories!) is probably Not Good.

    So takehomes?
    1. Personality tests are flawed! "Do you prefer to interact with a small group of friends or are you a social butterfly?" Not an actual question, as far as I recall, but they're a lot like this... and the answer is pretty much always "it depends"! Sometimes I love being the center of attention. Sometimes I need to find a bathroom to hide in for a bit. Preferences are very contextual.
    2. There's really no "best". Once you get away from the extremes - once you get within a certain bound of "acceptable" in each 'category' - everyone's a little different, and our similarities and differences make our relationships interesting and attractive.


    Back to HCA. HCA judges diamonds based on proportions from reports, scans, wherever you choose to get those proportions. As @sledge explained - HCA takes a subset of relevant numbers, those numbers are averaged and rounded, the backing data has accuracy and precision limits... When we say "look for HCA under X" what we're really doing is deciding where unattractive extreme should start. There's no best HCA score. HCA under 2 is the norm; I personally cap it at 3 as I think 2 is too restrictive - and what I'm doing by saying that is asserting that variance in diamond personality that result in variance in HCA scores under 3 can all be "interesting" and "attractive". Of course there are going to be flavours I like better, just as there are some people I like more than others...

    Let's use this question as an example:
    Do we know if, IRL, a stone that received an Excellent for Fire, as example, performs better than a stone that received a Very Good, etc?

    Let's say that "Good", "Very Good", and "Excellent" are all within the bounds of "acceptable" in each category - Fire, Scintillation, etc. "Excellent" certainly seems better than "Very Good", but the thing is - you personally shouldn't necessarily be aiming for the Jesus of "four Excellents". What you personally should aim for depends on your preferences and your context. I happen to adore RBs with high crowns, small tables, and short mains. My dream diamond doesn't get "Excellent" in a single HCA 'category'. That's because it's an extreme personality - it's less balanced, and HCA is doing more work than Myers Briggs in that HCA is positing a comparative declaration of whether or not the stone has achieved exceptional balance of a given characteristic compared to other characteristics... but I happen to find it more interesting and attractive than more balanced stones. And Very Good is still within my bounds of acceptable.

    Does a stone that receives "Excellent" for Fire perform better than a stone that receives "Very Good"? Well, if you compared those stones in-person,
    A) The "Excellent" scorer is probably predisposed to show more coloured light return across a variety of lighting conditions. Probably. It's not guarantee of actual behaviour - actual behaviour depends on a lot more factors than HCA intakes, and actual behaviour is contextual. Is more colour better?
    B) Brightness and fire can't coexist - white light return is higher-energy, and will drown out any single wavelengths (ie. single colours) that your pupil might have otherwise caught. To see colour you've got to limit brightness. Is less brightness in favour of more colour better? How much do you compromise? Do you prefer to compromise more or less than other people?

    The recommendation to use HCA as a blunt rejection tool is to prevent reading too much into each of those 'categories' - meet your stone, then find out more about its personality. Look at lots of stones and you'll find that you gravitate toward certain flavours that are represented by similar HCA scores. A lower HCA score isn't better.


    IMO if you're asking these sorts of questions about HCA you've passed its utility. It really is a blunt rejection tool - it'll help you cut through gobs of inventory quickly, but it isn't designed for fine-grained selection. I agree that the categories raise more questions than they answer - what is the proper way to use HCA? Are you supposed to be comparing strictly between stones? Or is it balancing different characteristics within a given stone? Is top grade (Excellent) in say Fire supposed to represent a quantitative measure of outputted dispersion (tons of it, vs. a little less of it) or a qualitative determination of how enjoyable that fire is (ex. Taking combative brightness into account)? The answers, of course, are "it depends" - enjoyability (heh) of fire also depends on facet size, which is primarily driven by stone size not optical symmetry... some RBs just sparkle more than others in every way, and are objectively more pleasing, but that isn't reflected by 4x "Excellent" vs. 4x "Very Good"... I would be interested in @Garry H (Cut Nut)'s thoughts. Full sentences kindly requested ::)
     
    Last edited: Aug 15, 2019 at 12:39 AM
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  10. Garry H (Cut Nut)
    Super_Ideal_Rock
    Trade

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    by Garry H (Cut Nut) » Aug 15, 2019 at 12:28 AM
    Also late for a meting. sorry.
    Did you buy a D Flawless Supa dupa ideal branded cut ?
    Everything about diamonds involves a trade off.
    Your extra girdle thickness will have little to no detriment to how the diamond looks and performs.
    And the other answers should help.

    The H&A's lowering is like the other symmetry raising lowering features - I added it because top sym helps the overall loss when a stone even with Ex sym can have a leakage spot here and there.
     
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  11. HDer
    Brilliant_Rock

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    by HDer » Aug 15, 2019 at 1:32 AM
    Thanks Garry. When would it be appropriate to check the H&A checkbox? Only when the scope image looks "excellent", or would it be appropriate even when the scope image looks "very good" according to these reference charts? https://ideal-scope.com/reference-chart-ideal-scope-images/

    I'm asking partly because different vendors seem to have different standards as to what they consider to be H&A.
     
  12. headlight
    Brilliant_Rock

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    by headlight » Aug 15, 2019 at 2:27 PM
    This is fascinating... I have a lot of family coming for the weekend and I think I'm going to have everyone do this lol!!!
    I like your openness to embrace stones that may fall a little outside the uber-ideal proportions as well as the recognition that there are different "looks" that appeal to different viewers. You do know what that sounds like, don't you... the "philosophy" of the GIA Cut Grading System lol! While it certainly has it's "flaws", I get the concept. I just think they need to make a revision... no shame in that... technology advances us and we need to change with the times. But that's a conversation for another thread of which I am planning to start in the coming days regarding some thoughts I want to throw out there about the GIA Cut Grading System.
    Anyhow, I do also feel that every stone has its own personality and those personalities will appeal differently to individual consumer preference. That's where I struggle a bit when certain stones are rejected here that probably are IRL very beautiful. I recently saw a video with Jonathon when he was still at GOG saying that selecting diamonds is about trade-offs (for most of us... I'm anxiously awaiting pics of Running With Scissors custom cut stone that I know will be TDF!). Even my long-time local jeweler I work with who is an AGS store and sells AGS stones and uses all the scopes, he feels that each stone should be assessed on its own merit, even if it doesn't totally fall within every narrow parameter range. But, again, he is selling diamonds in person (which has its own inherent plusses and minuses) which is a very different process than purchasing online.
     
  13. headlight
    Brilliant_Rock

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    by headlight » Aug 15, 2019 at 2:29 PM
    Thanks, Garry! YOU are "supa dupa" :)
     

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