Diamond Comparison

Diamond Comparison – The Fifth C

Diamond Comparison

Before deciding upon a specific stone, its very important to perform a Diamond Comparison side by side, because you could end up paying more than you need to, for a stone that is lower quality than you are expecting! Whilst diamond certificates give all the gemmological information you need when doing diamond research, the grading  system could end up penalising you without you even knowing it!

The one question that crops up time and again is:

How can the price of diamonds that have identical grades vary by as much as 20%?

The logical conclusion for most consumers is usually this; if diamonds with identical grades are really the same, why not just make a spreadsheet to compare them and then buy the cheapest stone? Many very smart people make the mistake of buying the certificate instead of actually performing a proper Diamond Comparison of the stones side by side with their own eyes!

Comparison of Cushion cut diamonds

Diamond Comparison of Cushion Cuts

The problem with grades on diamond certificates (whilst being correct in gemmological terms) is the fact that within each grade the range is far too broad to make a proper financial comparison. This means that more often than not, buying the certificate has two major negative consequences.

  • You could end up with an inferior stone
  • You could spend too much for it

How The Experts Buy Diamonds

Lets start with how the diamond trade determine a diamond’s price. Nature produces diamonds with a very broad range (range being the important word) of colour and clarity combinations. The problem that the Gemmological Institute of America (GIA) faced in 1953 when they invented the current diamond grading system was (and still is) where to draw the line to mark the change between grades? And this is exactly the reason why there is a pricing problem.

The GIA had to choose where to draw the line, so they determined that almost all retail diamonds would fall into seven broad grades of colour and clarity:

Colour D, E, F, G, H, I and J
Clarity IF, VVS1-2, VS1-2 and SI1-2

Each grade changes the price by roughly 15% and as this price increase is potentially a substantial amount of money, a consumer must be able to see a meaningful distinction in quality between grades (as well as within each grade). But even the best certificates can not provide the consumer with these distinctions because natures range doesn’t line up into these neatly defined categories because the lines are artificial (ie, man-made). Nature will create diamonds that are almost into the next grade up and of course, some that are almost into the next grade down. Some diamonds are right on the line between two grades providing a huge financial pitfall even for savvy consumers and experts!

Diamond experts instinctively sub-grade diamonds within each existing colour and clarity grade when deciding what the diamond is really worth. There is roughly a 10% price difference within each grade, and that’s for both clarity and colour, because you will get a good and bad sub-grade within each colour and clarity grade. E.g. a Good F colour which is almost an E, an average F colour, and a bad F colour which is almost a G. There are obviously dozens of possible combinations of prices of stones, some stones with good clarity and bad colour or bad clarity and good colour and so on, so any diamond within these grades even when honestly priced can vary between 5% to 20%.

So if you do Buy The Certificate in an attempt to get the best diamond at the best price, the likelihood that you will end up with a stone at the bad end of both colour and clarity is almost certain, and whilst the stone might cost 20% less, it may well be a stone that you wouldn’t have bought if you had compared several stones side by side.

Why you need to Compare

Here are three example diamonds that will illustrate why you should never Buy The Certificate and why you should always view a range of diamonds side by side to perform a Diamond Comparison. In this example you will see a good VS2 versus a bad VS2, and the bad VS2 versus a good Si1, all these stones are G colour and all have a GIA cut of excellent to maximise their brilliance (so if you compared all three side by side with your eye, at first glance they would all look fabulous).

Good VS2 Round Diamond

Good VS2 Round Diamond

The above stone has three tiny imperfections circled in red in the image on the left taken from the GIA certificate. The only reason that this stone is not a VS1 is because of this group of imperfections that are reflecting in the facets and because under magnification and from certain angles these three marks actually look like seven marks instead.

Bad VS2 Round Diamond

Bad VS2 Round Diamond

The above stone is the bad VS2, it has many more imperfections around the edge and far more serious imperfections in the centre (which is called the table). If you compare the stones you will see there is a huge range between them even though they are the same grade. We would almost certainly reject the bad vs2 when compared side by side with the good vs2. But some online diamond retailers might price all stones of the same grade (good or bad) at the same price, others might discount the bad stone that experts wont buy. This entices consumers into buying a stone at the bottom of a grade believing they are getting a great deal for a stone at the top end of that grade. Either way the consumer loses.

Good Si1 Round Diamond

Good Si1 Round Diamond

The above image shows the good Si1, a full grade down from the VS2 and a lot less expensive. It has a similar cluster of imperfections in the table as the bad VS2. In fact both stones are right on the mad-made line between VS2 and Si1. The si1 is remarkably similar to the VS2. When you compare the bad vs2 and si1 side by side they look pretty much the same gemmologically, but when you compare the price, the difference in cost is incredible. For example, a 1ct VS2 would be around £1000 more expensive than a 1ct Si1. A 2ct VS2 would be roughly £5000 more expensive than a 2ct Si1 and the difference in price at 3cts is roughly £20k!

Perhaps the Good VS2 versus the Good Si1 is worth that difference, but no diamond expert would pay a significant difference for the bad vs2 than for the good Si1. But that is more often than not what a consumer gets when they Buy The Certificate. So, with the crazy range of possible combinations of colour and clarity grading, the important question that a consumer must ask is:

How do I know that I’m getting what I think I’m paying for?

How the Diamond industry works

Diamond cutters understand everything that we have described above, and they bear it in mind when deciding how to sell their stones. They sell to two different markets; first they sell to professional dealers or brokers (like us) where all such buyers are experienced. Every stone is examined under 10x magnification before a penny is parted with, and the only way that the diamond cutter will make a sale on a stone at the bad end of any grade is to discount it. Second, they supply lists of certified stones to online retailers like bluenile or 77diamonds (not the stones themselves, just a list of stones).

Now imagine for a minute that you are a diamond cutter, and you have hundreds of certified diamonds. Some at the top end of each grade and some at the bottom. Now ask yourself which half of your stones you would keep to show your repeat trade customers who will personally perform a side by side Diamond Comparison, and which half you will list for sale online, to be sold to an inexperienced one-time consumer who cannot perform a Diamond Comparison before buying? So just how are the diamonds you see listed online actually priced? The answer is All over the place! The point is that there is no way to know from the certificate which is which!


You don’t need to buy a diamond, unseen, from an online diamond retailer or drop-shipper to get the best prices. You can get the best of both worlds at Daniel Prince. Whether you prefer to compare with your own eyes or to buy online, as diamond brokers (not owners), we only recommend diamonds that we would buy ourselves! We (or our trusted associates) personally perform a Diamond Comparison of several stones that are chosen especially for you because our number one priority is to make you a happy (and repeat) customer by guiding you towards the right stone at the right price.

Now that you understand the financials, and potential pitfalls, when choosing a diamond, remember to also be a romantic because this purchase is one of the most emotionally important in your life. It is also as much about the perfect ring design and the craftsmanship as it is about the diamond, and you should also budget for a high quality custom engagement ring to not only show off your diamond but to protect your investment!

We would be delighted to show you a range of stones handpicked just for you to illustrate the 4C’s and answer any questions you may have. Just contact us to book an appointment!


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