The cut of a diamond is by far the largest factor that determines its beauty. The better the cut, the better the brilliance and sparkle of the diamond. If the stone is cut is too deep or too shallow, light that enters the diamond will leak through it. This is why poorly cut diamonds often look darker and lack life.

physics of light travel within a gemstone

Cut is said to be the most important C as it has the greatest bearing on the gem’s appearance. Personally, I fully agree with this statement. After all, why would you even want a diamond that is dull and lifeless?

Cut is a Pre-Requisite For Selecting Any Diamond

Cut grade is the objective assessment of the gem’s proportions and finishing. In grading reports, the cut grade is assigned as a combined rating of these 2 aspects. Using the GIA system as an example, diamonds can be classified into various grades such as Excellent, Very Good, Good, Fair, and Poor. As much as your budget allows, you should ALWAYS strive for a better cut grade in a diamond.

Ok, I know you are probably thinking… “Why are you telling me this? I know that cut is important. As long as I choose a GIA triple excellent diamond, wouldn’t all my problems be solved?” Here’s what most people don’t know. While the GIA grading system can provide a fairly good assessment of the diamond’s brilliance, GIA also allows a wide range of proportions to exist within their triple excellent ratings.

This means that 2 diamonds with GIA triple excellent ratings might not necessarily look and perform the same. Ultimately, the subtle differences in proportions and facet alignment will affect the stone’s interaction with light. To help you decide which diamond has better performance, you need to go beyond what the grading report says and perform a deeper analysis.

You can find examples of truly well-cut diamonds at and to help you benchmark and compare diamonds.

Using the Holloway Cut Advisor (HCA) as a Weeding Tool



The simulation software used in the video can be found here => Holloway Cut Adviser
Click this link to learn how to use the HCA tool.

size of a 1 carat diamond compared to a 0.5 carat diamond

A Comparison of 2 Diamonds

Before you get too carried away by numerical numbers, there’s something I want to tell you upfront. Numbers and cut grades indicated on a grading report are not cast in stone and they are only meant to be used as a guideline.

Why? Even if the HCA tool returns a similar result for 2 diamonds with similar proportions, they would still handle light differently in real life. For more details, read this article to find out why the HCA software can often lead to disastrous shopping outcomes.


Generally speaking, I would recommend you to reject stones that score higher than 2.0 on the HCA. A diamond with a score of less than 2.0 passes the first test and warrants a closer examination. Remember, the Holloway Cut Advisor is a “rejection” tool and not meant to be used a “selection” tool.

So, what’s next after you narrow down your initial selections? How do you take the analysis of your shortlisted diamonds to the next stage? Thankfully, there is a simple tool called the Idealscope which allows you to determine a diamond’s optics in an objective manner. Find out more on the next page…

Related Articles

Sharing Is Caring ! Share on Facebook0Share on Google+0Tweet about this on TwitterShare on LinkedIn0Share on Reddit0Share on StumbleUpon0


  1. Ben-
    March 3, 2015 at 4:08 pm

    Hi Paul,

    Thanks for what may be the *best* diamond learning site out there, no joke. I’ve been researching about a month now, and I wish I had found your site earlier! On the other hand, I’m just glad I haven’t bought anything yet. I’ve already avoided many, many pitfalls, and am now aware of more due to your site. This brings me to my question:

    I’m now using the HCA to reject what seem like “good” stones based on the GIA report. I’ve rejected numerous Triple Excellent stones and am beginning to wonder if finding a 0-2 HCA is out there. I’m using mainly James Allen because I want to see the 360 views.

    I’m looking for an eye-clean (SI1, H-I, 6.5 to 6.8 mm) stone that has an HCA of 0-2 and shows a nice scope image. If we email or PM I will share my budget with you.

    Can you help?!!

    The good thing is I am not in a rush and have time, so I’m starting early. But I also have a science background and so am unwilling to succumb to marketing tactics!


  2. Alex Lane-
    September 22, 2015 at 2:03 pm

    Thank you so much for your insight! I am getting close to proposing and trying to find the right ring. I have no idea what I am looking at. I saw one that I liked a lot and it seemed like a good price, but I can tell now that the diamond was too deep. I’ll have to use this as a reference guide.

  3. Fancy Cut-
    August 8, 2016 at 1:30 am

    I am having a hard time finding a well cut heart shape diamond. Base on your suggestions, HCA tool has “rejected” most of the diamonds with fish-eye problems. I am not sure if there is another set of criteria when it comes to heart shape diamonds, or it is just hard to find.

    Would you kindly provide some guidance?


  4. Paul Gian-
    August 8, 2016 at 7:39 am

    The HCA tool is not applicable to heart shaped diamonds. To find out more about choosing well cut hearts, read this:

  5. Marina Battifora-
    February 1, 2017 at 11:58 pm

    I am about to buy a 2ct marquise diamond. You said that CUT is very important but they don’t specify the cut in the marquise. The one I’m looking is G/SI1, no fluorescence, GIA, in my area. I cannot afford Allen’s prices so could you tell me what I should look for in the diamond?

  6. Paul Gian-
    February 2, 2017 at 2:16 am

    I’m afraid you are just setting yourself up for disappointment if you shop with this kind of mindset. Read this:

Leave A Comment