Graduated Milgrain Diamond Engagement Ring in 14k White Gold Blue NileGraduated Milgrain Diamond Engagement Ring in 14k White Gold Blue Nile

How to Buy a Diamond Online (Tips and Tricks)

If you want to buy a diamond online rather than at a brick-and-mortar store, you’ll need to be well-informed about these stones. These 7 top tips can help.

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HomeDiamond AdviceDeciding Where to Buy a DiamondHow to Buy a Diamond Online (Tips and Tricks)

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There are several reasons to buy a diamond online rather than through a brick-and-mortar retailer or broker. You can shop from the comfort of your couch and face less sales pressure. Online retailers also have thousands more stones "in stock" than your local jeweler. However, shopping online means you'll need to be more informed about diamonds. After all, you won't have a salesperson to answer your questions in real time. In this guide, I'll reveal the secrets to buying a diamond online.

The Four Cs of Diamond Grading

Everyone's diamond education starts at the same place. It doesn't matter if you take a friend's advice or jump on the web and start your own research. You'll run headfirst into the Four Cs of diamond grading — color, cut, clarity, and carat.

Developed by the Gemological Institute of America (GIA) in the 1950s, this system simplified an inherently complex subject. It set the standard for communicating diamond quality in an easy-to-understand manner. Retailers began to use this system to classify and value their diamonds. As a result, consumers were comfortable they had enough knowledge to make an expensive purchase.

However, the Four Cs system is a dramatic over-simplification. Most consumers assume that diamonds with the same color, cut, clarity, and carat weight are the same, so they just shop for the stone with the lowest price that has the grades they want. Unfortunately, diamond quality doesn't work that way. Consumers often make critical mistakes, especially in the areas of cut and clarity, when they buy a diamond online.

Professionals in the diamond industry know how to look beyond the grades. They know how to find the idiosyncrasies in every stone.

buy a diamond online - solitaire Engagement Ring Blue Nile
1-ct round brilliant cut in 6-prong solitaire. © Blue Nile.
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at Blue Nile

Imagine the Four Cs in Terms of Rarity and Beauty

Before shopping online, think about what diamond qualities are most important to you. In other words, prioritize the Four Cs according to your needs. This will give your search a better starting point.

The cut should rank first or second, whatever your other priorities are. Simply put, cut plays a major role in the beauty and performance of every diamond.

What Makes a Diamond Rare?

I like to think of clarity and carat weight as being two characteristics responsible for the rarity of the stone. Clarity and carat have little effect on the beauty of the diamond. However, they're better indicators of how rare a particular stone is in relation to other stones available on the market. Diamond isn't a rare mineral in the Earth, but diamonds with high clarity and/or in large sizes are harder to find for sale.

What Makes a Diamond Beautiful?

Color and cut both have a great effect on the overall aesthetic beauty of a diamond. Viewers will easily notice these two characteristics.

Cut describes not only the shape of the stone but also the positioning of the facets — those flat surfaces cut into the diamond. If done well, this positioning will emphasize the stone's brilliance or brightness. A diamond's dispersion or "fire" (the spectral colors it may show) and its scintillation or "sparkle" also depend on the cut.

buy a diamond online - Graduated Milgrain Diamond Engagement Ring in 14k White Gold Blue Nile
This updated 2-ct oval brilliant-cut center diamond stands out among diamond accents along the shank and milgrain details. © Blue Nile.
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at Blue Nile

Color measures the degree or lack of color that a diamond displays. Diamond color will most likely be the first quality a viewer will notice. For white diamonds, stones closest to colorless receive the highest color grades. 

buy a diamond online - J color diamond Blue Nile
J color diamond. © Blue Nile.

Now that you have a general understanding of the Four Cs, let's cover the best tips and tricks that will help you buy a diamond online.

Tip 1: Don't Buy "Off the Numbers"

White, round brilliant-cut diamonds are one of the most popular color-and-shape combinations. So, I'll start with them as an example.

Let's say you find two round, brilliant-cut diamonds, both with Excellent cuts, the best grade. Will they perform the same way? Not necessarily.

Diamonds with the same cut grade can still differ dramatically in how they handle light, which is what makes diamonds beautiful. Round diamonds of the same cut grade can also have huge price variations, as much as 20-30%, based on their "make." A stone's "make" refers to the overall quality and character of the cut. Nevertheless, their grade reports look identical. Why?

A grade report can't capture the make, even if you know the optimal proportions and percentages for a specific cut and/or shape, like a round brilliant. In fact, in the trade, this is known as buying "off the numbers," over-relying on the grade report. In my experience, consumers who buy off the numbers generally end up paying more. Due to overconfidence in their "research," they pay for things that don't matter or that they don't truly understand.

The Numbers Don't Always Add Value

Take another example. I once helped a friend make an engagement ring using a stone he provided. He was totally convinced he got an "amazing" deal on a modified cushion cut. He bought it online for 20% cheaper than anything comparable.

When I compared the stone to the numbers on the grade report, two issues jumped out at me. First, the "make" of the stone was fair, not excellent. The document indicated that the girdle was "very thick." Second, based on the stone's weight, 1.62 carats, the face-up size seemed small. I decided to investigate further.

The gem cutter left at least 0.25 carats of weight in the girdle to preserve weight. Thus, the diamond weighed 1.62 cts "face-up" but looked and measured like a diamond around 1.30 cts. The cutter did that because there's an inflection point in price above 1.50 cts. If he left the girdle thick, eventually, someone like my friend would pay more for that stone than for a better cut cushion of the same face-up size that weighed 1.35 cts.

Simply stated, an uneducated consumer will pay substantially more for an inferior 1.62-ct diamond than a superior 1.35-ct diamond. A dealer, betting on that fact, stocked the stone. He then sold it to my friend at a "big discount" to comparable stones.

My friend paid for 0.25 carats of weight that he literally can't see. It adds no value to the face-up size of the stone. In fact, that weight negatively impacts the stone's optical performance, yet it still got a cut grade of Excellent. (For a way to help spot "invisible weight," see Tip 6).

Tip 2: Your Metal Color Choice Can Affect Your Diamond's Color

If color is one of your top priorities, carefully consider the metal setting for your ring or other jewelry piece. If you want a white gold or platinum mounting, it may make sense for you to buy a white diamond with a high color grade, as close to colorless as your budget will allow. However, if you choose yellow or rose gold, keep in mind that the diamond, once set, will reflect the metal color. Colorless stones won't look as colorless as they should.

In my opinion, putting a colorless diamond (grades D, E, and F) into yellow or rose gold is a waste of money. Instead, consider buying a white diamond with a lower color grade. The reflection of the yellow or rose metal color will have less of an impact on the color of these stones. In fact, stones with lower color grades may actually appear whiter in yellow or rose gold settings. A less expensive J or K color would display just as beautifully as a more expensive F or G color.

Emerald Cut Diamond Engagement Ring in Platinum Blue Nile
1-ctw emerald-cut diamond engagement platinum ring. © Blue Nile.
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at Blue Nile

Tip 3: Ask the Online Retailer About a Tinge or Modifying Color

Some diamonds have a secondary modifying color not indicated in the grade report. This can cause what dealers call a "tinge." Usually, stones with a brown, green, or gray tinge are less desirable.

Before you buy a diamond online, contact the retailer and ask them if the stone shows any indication of a tinge or modifying color.

Tip 4: Your Diamond Shape Choice Can Affect Your Diamond's Color and Performance

If you choose a fancy cut diamond, which means anything other than a round, be aware that certain shapes display the color differently than rounds.

For example, the long slender facets of an emerald-cut diamond will wash out the stone's color, unlike the "busier" faceting patterns of rounds, cushions, marquises, and ovals. With an emerald cut, you could find a nice, white stone graded as low as an L color.

Shapes such as ovals, marquises, pears, and sometimes hearts can show a "bowtie effect." These shapes may have a dark, bowtie-like area across the center of the stone. This is caused by the depth and positioning of the facets.

Tip 5: Trust Your Eyes

Professional gem graders evaluate diamond color by viewing the diamond through the girdle. Thus, the color on the grade report is the "body color" of the stone. However, most consumers are interested in the "face-up" color, which isn't recorded on a grade report.

When judging the face-up color for yourself, trust your eyes. 

If clarity is one of your top priorities, prepare yourself for high prices. Clarity is responsible for the biggest price jumps between grade levels. Since a diamond's clarity is graded under 10X magnification, you'll need a loupe or microscope to tell the difference between a VVS1 from a SI1 grade. However, you'll see the price difference with the naked eye just fine.

As with face-up color, when judging diamond clarity for yourself, trust your eyes. Look for "eye-clean" stones, diamonds that look clean to the naked eye.

(That said, I've had the privilege of sitting with several clients who always dreamed of owning a particular clarity grade. Anything less just wouldn't do). 

Tip 6: Check the Diamond's Dimensions

If you're looking for the largest diamond you can afford, find out what that diamond's dimensions should be at that specific carat weight. Consult this chart. For example, a 1.00-ct round, brilliant-cut diamond, if cut to its best make, will measure 6.40 mm across the top of the stone. If you would rather have a 1.50-ct, emerald-cut diamond, then it should measure approximately 7.50 x 5.50 mm.

Once you know what the dimensions for your stone should be, you're better able to judge if the cutter added "invisible weight" to the stone.

Some people prefer an emerald cut with a long, rectangular shape. Others prefer something shorter and almost squarish. Checking an emerald cut's length-to-width ratio is a good way to search online for the type of shape you want. This ratio is determined by dividing the stone's length by the width. (You might find it written as L/W or L:W).

If you prefer a longer emerald cut, you'll want to look at ratios from 1.50 to 1.60. For a shorter stone, look for something under 1.45. (A ratio of 1 is, of course, a square).

Consumers are often unaware of the length-to-width ratio's significance. Some grade reports may not include it. However, some online retailers like Blue Nile will let you filter your diamond searches by L/W ratio.

Three-Stone Emerald Cut Diamond Engagement Ring in 18k Rose Gold Blue NIle
5/8-ctw three-stone 18k rose gold engagement ring with emerald and oval-cut diamonds. © Blue Nile.
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at Blue Nile

Tip 7: Use the Services a Retailer Provides Before You Buy a Diamond Online

Inspect the diamonds you find online from all the angles the retailer provides. Thanks to improvements in internet speed and video compression, online diamond retailers like Blue Nile provide magnified 360° videos of some of their diamonds. These videos will give you a good idea of the diamond's performance. While it's not the same as seeing it in person, it's certainly the next best thing!

Blue Nile also allows you to filter searches for stones in their inventory that have full 360º views. This is a great benefit to consumers.

Many online jewelers also offer the ability to chat online with a diamond expert. If you'd like someone to walk you through your options, you can schedule a virtual appointment at no extra cost. Check out this link to Blue Nile's virtual appointment page for more details.


I hope these tips and tricks will help you buy a diamond online. There are real opportunities for you to find a stone at a great value. Remember, determine what diamond qualities are most important to you and start your search there.

Jake Talve-Goodman, GG

Jake Talve-Goodman GG serves the St. Louis, Missouri community as a gemologist, designer, and appraiser. His passion for gemstones and minerals began at an early age of 8 after finding a significant crystal specimen in the playground of his elementary school. After graduating from the Gemological Institute of America with the Graduate Gemologist designation, he spent years working for private boutique jewelers and inside of a gemological laboratory inspecting salvaged jewelry items for repair and resale from the insurance industry.

Today, Jake operates The Concierge Gemologist, a professional jewelry service that meets clients in the comfort of their own home, around their banker’s desk, or lawyer’s office. The Concierge Gemologist provides appraisals according to the standards defined by the Uniform Standards of Professional Appraisal Practice (USPAP) to ensure the highest degree of service in the industry.

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