A Comprehensive Guide to Buying a Diamond

Updated May 9, 2019 to add tips from a professional jeweler.

My engagement ring. (Photo: Arctic Weddings Iceland)

Before my husband and I got engaged in 2017, I told him I wanted to be involved in the engagement ring selection process. In part because it’s my personal belief that the ring is symbol of the pact between two adults, and thus the burden of decision ought to be shared, but also because jewelry is a great passion of mine (not so much his) and I knew I wanted a part in it. And while there’s been an uptick in gemstone engagement rings (I’ll be writing another piece on selecting a gemstone engagement ring), this is going to be a guide in selecting a natural diamond.

The anatomy of a diamond

Pay attention to certification

Before you spend any kind of real money, make sure you know if the diamond is certified and by which entity. A certified diamond ensures that your purchase will retain its value, but not all certification is created equal. The two largest certification labs in the US are the GIA, the Gemological Institute of America, and EGL-USA, European Gemological Laboratory’s USA arm. But if value is your goal, we recommend only considering GIA stones, as it is the gold standard of grading systems not just in the States, but globally.

The GIA possesses the strictest criteria and is responsible for establishing the four “C’s,” which is now the primary diamond grading system used worldwide. Paying for GIA certification is more expensive for retailers, however, which is why you often see EGL certification used for diamonds one carat or less, but don’t be fooled. Even though EGL uses the same terminology for grading stones as the GIA, their criteria and implementation is more lax.

What also sets the GIA apart is that every stone is anonymized and graded separately by multiple expert gemologists, who then agree on a finalized grade, so it’s harder to “game” the process. Each diamond is also given a micro-laser inscription with its own report number so GIA-certified diamonds can be tracked. If you have your diamond’s report number, you can even log onto the GIA’s database to view your report.

Know your four “C’s”

They are carat, cut, clarity, and color. Now here’s why each are significant, and how you can save on each of these:

Carat is unit of mass used for measuring diamonds and other precious stones. Technically, a carat amounts to 200 mg of weight, and despite what you might have heard, the cost of the carat is the same regardless of your cut. Carat weight also is critically important into determining the unofficial fifth “C”… cost. As your carat weight goes up, so does the price-per-carat, which means the price-per-carat for a two-carat is less than a three-carat stone. You’ll save significantly by going just shy of a full carat weight, so if you’re looking for a two-carat, you’ll save by getting a 1.90 carat, and the weight difference is practically imperceptible.
Cut refers to the balance of a diamond’s polish, symmetry, and thus, its ability to refract light. Of all the “C’s,” cut is arguably the most significant for aesthetics. Sometimes, it’s worth sacrificing on weight for a better cut, since a well-cut diamond has brilliance and fire, whereas one that’s been poorly cut looks dull in comparison. The quality of the cut also factors into the price-per-carat of the stone. In our opinion, it’s actually the most important of the “C’s.”
Clarity comes on a scale set by the GIA and refers to the number of inclusions within or blemishes on the surface of your diamond. The placement and size or these imperfections, or lack thereof, can impact the cost of your rock, but in our opinion, it’s the least important if the “C’s” so long as the stone is eye-clean. However, inclusions can negatively affect the quality of your diamond and even the durability of the stone. If you’re curious to know more about inclusions, you can check out this guide.
- FL - Flawless is the rarest (and needless to say, priciest) on the scale. It means that even under 10x magnification under a loupe by a trained eye, there are neither inclusions nor blemishes visible.
- IF - Internally Flawless is also quite rare, and it means while there are blemishes on the surface of the stone, there are no visible inclusions visible under 10x magnification.
- VVS1 and VVS2 - Very, Very Slightly Included 1 and 2 means that only under 10x magnification are extremely slight inclusions visible. VVS1 means the inclusions are located in the bottom half of the stone (the pavilion) while VVS2 means the inclusions are in the top half (the crown).
- VS1 and VS2 - Very Slightly Included 1 and 2 means that the inclusions are a tad bigger, but are still generally invisible to the naked eye. According to Lumera Diamonds, only one in 100 untrained eyes can detect a VS2 inclusion.
- SI1 and SI2 - Slightly Included 1 and 2 is the next step down, but the inclusions are still quite difficult to see, and then only under extremely close inspection. SI1 is also the last grade on which the stone can be eye-clean, which means the inclusions are invisible to the naked eye.
- I1, I2, and I3 - Included 1, 2, and 3 means the inclusions are more noticeable with 1 being the least to 3 being the most included.
Color refers to the scale of the presence of the color yellow in the rock. While fancy diamonds are a whole thing on their own, when it comes to choosing a colorless diamond, the lack of any yellow is actually what’s prized. The color scale set by the GIA has been widely adopted and ranges from grades D to Z, though D through M are going to be what you most commonly come in contact with along your search. Price note: There’s usually a seven percent to 10% price difference from one color to the next.
- Colorless: D, E, F
  - D, E, and F diamonds are in the top tier of colorless diamonds, and between then, there is only a subtle difference in color that is only noticeable when they are compared side-by-side. Ideally, these stones should be set in platinum or white gold, or at least with prongs made with these metals, since a yellow or rose gold will reflect into the stone. If you’re paying a premium for the color, make sure it really pops.
- Near Colorless: G, H, I, J
  - This next level is a great deal, especially G and H colors, since they’re still relatively colorless and differences are only noticeable when they’re held up to a colorless stone.
- Faint Color: K, L, M
  - The color becomes more noticeable in the next range. If you have your heart set on a yellow gold setting, consider a diamond from K, L, or M as they’re warmer and will complement the metal. Also, set into yellow gold, the stone actually appears whiter and you’ll definitely save money on the rock itself.

If having the best-priced nearly colorless, eye-clean two-carat stone to the untrained eye possible, aim for a 1.90 carat, ideal cut, H color, SI1 stone.

What to know about each shape

Round Brilliant

Most common shape out there which means there’s the greatest inventory
The only shape for which the GIA has a measurable cut standard for symmetry
Can possess the most brilliance (AKA dispersion of white light) and fire (AKA flashes of color) of all the cuts, thanks to 58 well-placed facets
Commands the highest price tag due to the amount of raw stone that must be lost to achieve the shape

Princess Cut

This cut is great for using a greater percentage of the raw stone while still being able to retain considerable fire and brilliance
A forgiving cut for inclusions, as the facets are good at hiding them
The corners are the weakest part, so should be protected by prongs
You can get more stone for the price with a princess cut, since there’s less waste

Cushion Cut

A brilliant cut, cushions are real sparklers as they can have considerable radiance, though not as much as a round
They’re also a cheaper cut compared to the round, even though they’re an older shape
They show a lot of their color, so if they’re best in the colorless and near colorless range
Elongated cushions can make your fingers look longer

Asscher Cut

The Asscher has a clean geometric shape with a visible “X” in the center
A step-cut, the Asscher carries most of its weight below the table (top surface of the diamond), so from the top, it can look smaller than other cuts
The Asscher has 58 facets while the Royal Asscher has 74 facets, which means the latter has increased flashes of color, but overall, the Asscher is not one of the more sparkly cuts
It’s a less common cut, and thus, more expensive than other shapes

Pear Shape

A graceful fancy shape, pears have been making a comeback in recent years
The facets are placed to optimize scintillation, so a well-cut pear can have quite a bit of radiance, but it also shows more color than a round
When selecting a pear, symmetry (i.e. even shoulders, belly, and wings) is crucially important
Make sure the table and culet (the bottom point in a diamond) is centered
While bowties (a bowtie-shaped darkness in the stone, common also in oval shapes) are hard to avoid, the darker the bowtie, the less optimum the cut
The point is the most vulnerable part, so make sure it’s protected in the setting

Radiant Cut

Radiant cuts have an eight-sided outline and has and mix of step cuts in the crown and brilliant cut facets in the pavilion for maximum sparkle
Shows a lot of color, so is great for fancy diamonds, but less so for colorless stones
Watch out for uneven corners or an off-center culet in a radiant
Radiant cut can come in a square or rectangular shape, the choice is up to you

Emerald Cut

Another step-cut fancy shape, the emerald cut isn’t great at hiding inclusions, and is best with a higher clarity stone
It also shows more color than a round, so for a colorless stone, you’ll want something higher on the scale
Because of the fewer number of facets and its shape, the emerald cut gives off less scintillation, but has a really clean look
The elongation of the emerald cut can make it appear larger than a round or Asscher of the same carat weight, but it’s also one that carries a considerable weight below the table, so will look smaller than say a radiant or oval
The shape has a classic-yet-modern minimalist appeal, and it works in nearly every setting, though we recommend going with a solitaire or side diamonds and no halo

Oval

The oval shape is cut for maximum brilliance and fire and a great, timeless alternative to a round
Just like with the pear, you’ll want to watch out for a bowtie in the oval shape, as it can mean a poorer-quality cut
This is another cut that does well with hiding inclusions and blemishes
The oval holds more carat weight on the top, so can give the appearance of being a larger stone
The elongated shape can be slimming on fingers

Marquise

The marquise shape has 56 facets and possesses plenty of fire when cut well
Its elongated shape can also be slimming on fingers, and can give the appearance of a larger stone than squatter shapes
Bowties can also be an issue with marquise shapes, so be wary when you’re shopping for one
Like ovals, there are a variety of length-to-width ratios out there, so it depends on what your preference is
It’s definitely a rarer cut, so if you’re on the market for something more unique, the marquise might be what you’re looking for

Tips from a professional jeweler

While having a GIA report is great in hand, it often doesn’t give you a clear idea of what the diamond will look like IRL, so Ashley Zhang of Ashley Zhang Jewelry recommends seeing the product before you buy and also seeking help from a professional.

“I would recommend working with a jeweler or an expert because you cannot tell everything about how a diamond looks in real life just off a report alone,” she tells us. “Two diamonds of the same report grades can look completely different and can be priced differently. That’s why I tell people not to buy online. ” Working with a pro also comes with the added benefit of having access to diamonds that are otherwise not available to those outside of the industry.

Another argument for seeing a rock in person is so you can see how much it really sparkles. "Measurements such as the spread [of the table] and depth [of the stone] can have huge impacts on how the stone looks in person and reflects light,“ Zhang says. “This can also greatly affect the price.”

Questions to ask yourself about the setting

When choosing a setting, here are a few questions to ask yourself before you buy.

Are you looking for a four-prong, six-prong, or bezel setting for your stone? Sometimes the best setting will be dictated by the shape you select.
What kind of metal do you want: white gold (14K, 18K), platinum, palladium, yellow gold (14K, 18K), rose gold, or something else?
Are you planning to wear a band with your ring? If so, consider a flush fit engagement ring that allows your band to sit flush against your engagement ring, or a curved wedding band that will complement your stone.
Do you remove your ring often? Ask your jeweler about creating a ring with comfort fit, which means the ring will be rounded on the inside, so it slides on and off your finger smoothly.
Are you considering side stones? If so, know that while they add to your overall carat weight, they will cost additional. There’s also a huge variety to select from, so consider one that complements your center diamond.
Do you want a pavé band or would you prefer something channel set? If so, do you want it to go halfway, two-thirds, or all the way around? Graduated stones or all the same size? Know that an eternity band (one that goes all the way around) cannot be resized, and your finger can swell and change sizes throughout your life.
Do you want any additional detail on your ring such as milgrain beading, filigree, and accented gallery for your diamond, or a cathedral setting?
To halo or not to halo? The eternal question. Pros of a halo is it can make a center stone appear larger, and thus pack a greater overall wow factor. However, a con is that it can detract your attention from a truly spectacular center stone. Additionally, the halo trend comes and goes, and so your ring can look dated from time to time, but a solitaire will never go out of style.

Feature Photo Credit: Ashley Zhang Jewelry