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Why this article?
This article is for anybody looking to buy a loose diamond (either by itself or with an engagement ring as a “build your own” set) online at one of the many online diamond vendors.
If you’ve been around my site before, you’ll see that I generally recommend buying from James Allen. For an explanation of why that is, see here: James Allen vs. Blue Nile and here: Truth About The Diamond Pro. Likewise, you can read my individual site reviews for James Allen and Blue Nile.
What Carat Weight Range Should I Choose?
This is probably the most important question you will ask yourself when buying loose diamonds, because compared to all the other factors, carat weight has the greatest effect on a loose diamond’s price.
Additionally, carat weight is of supreme importance because this is what will primarily determine the size of the diamond you buy. What are your fiance-to-be’s expectations? Is she expecting a 2 carat diamond? Will she be disappointed with a 0.50 carat diamond?
These are crucial issues, so make sure to do your research thoroughly before you buy. If you can’t speak to her about it, try to speak with her friends or family. In most cases, the answer will be “the larger the better,” but it’s always good to know what her minimum expectations are.
What Shape Should I Choose?
The second most important issue you’ll have to figure out when buying a certified diamond is what diamond shape is your girlfriend expecting? The answer to this question is purely a matter of aesthetics. There’s no calculation you can make that will tell you what she wants.
For this question, more than any other, try consulting her friends. Very probably, she’s mentioned it before to one of them. If you simply can’t get the answer, and you absolutely do not want to ask her, then the safest bet is the Round Brilliant.
The Most Common Shape
Rounds are the most common diamond shape by far. Most sites have a 30-day return policy, so if you order it close enough to the proposal date, and you get it wrong, you can always send it back and buy what she really wants.
Keep in mind, however, that shape can affect a loose diamond’s price. All else being equal, round brilliant loose diamonds cost more than the other shapes (generally called “fancy shapes”).
The reason for this is that round brilliant certified diamonds have a much lower yield-from-rough than the other shapes.
What Diamond Cut Quality Should I Choose?
The first two questions simply set the stage for the real technical decisions. Now that you know how big of a stone you need and what shape it should be, you need to decide on the Cut Quality.
Cut Quality will also have a notable effect on the price of loose diamonds. Choosing a cut quality can be tricky, however, since cut grades are not standardized at all across the different vendors.
Some vendors only offer a cut grade on their round diamonds and base them on the certificate’s cut grade (with the exception of AGS, the labs do not offer cut grades on fancy shapes).
Choosing Between Certificates
Other vendors disregard the certificate’s cut grade altogether on rounds and fancy shapes, and use their own matrix of cut grades based on the diamonds’ measurements.
Combining these different strategies in a meaningful way is difficult to say the least. Whenever possible, you should use the certificate’s cut grade over and above the individual site’s cut grade.
My advice for cut grade is this: If you are looking for a round brilliant diamond, only search for “Ideal/Excellent” grade diamonds. If you are searching for a fancy shape, however, then it might pay to either include “Premium” or to disregard the cut grade altogether.
This is not to say that cut grade is not important – on the contrary, it’s of utmost importance. It’s simply saying that many vendors don’t correctly report fancy shape cut grades, so why filter out many results from your search which might be great choices.
What Color Grade Should I Choose for loose Diamonds?
More so than a Diamond’s Clarity, a Diamond’s Color has a serious effect on both a loose certified diamond’s appearance and price. For recommendations as to the best color to choose for the best value, see our article about diamond color.
It is important to remember that different shapes reflect color at different strengths, so your choice of optimal color balancing the diamond’s appearance with the diamond’s price will depend greatly on what diamond shape you’ve chosen.
What Clarity Grade Should I Choose?
As opposed to Color and Carats, I like to think about Clarity not in terms of a sliding scale of grades, but as a binary grade. What I mean by this is that all I care about when evaluating clarity is whether or not a loose diamond is clean to the naked eye.
If it’s any cleaner than that, it’s just going to cost you more money without giving you anything back in return. You’re better off buying the lowest possible clarity grade that is still clean to the naked eye and using the money you saved to either buy yourself a larger diamond or a diamond with a higher color.
Evaluating Clarity Online
With most vendors, this isn’t possible because you can’t see the diamond before you buy it. James Allen, however, lets you get beyond this hurdle. With their “Virtual Loupe” you can evaluate a loose diamond before you buy it. Brian Gavin & Zoara also offer high quality photography.
If you have any doubt as to whether or not a stone’s inclusion pattern will be clean to the naked eye or not, please feel free to email me a link to the stone and I’ll be happy to take a look for you and give you my educated opinion.
For an informative overview of the different clarity grades, take a look at this diamond clarity chart.
What about Fluorescence, Polish, and Symmetry?
These will also affect a stone’s value (but not necessarily its appearance) to some degree, although much less so than the factors mentioned above. For an in-depth discussion of each of these three factors, please see these individual articles: Fluorescence, Polish, and Symmetry.
Which Diamond Lab’s Certificate Should I Look for with my Loose Diamond?
You should stay away from IGI, EGL, and HRD Certified diamonds because I have found in my professional experience that their results cannot be relied upon due to their consistent inconsistency in grading.
Feel free to read the articles I wrote on each individual lab linked to above.
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