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diamond ring

Costco makes purchasing the highest quality diamonds easy by offering only the industry's highest quality diamonds at the lowest possible price. Our long-standing relationship with our suppliers guarantees we get the best selection at the best value. Costco's experienced buying team works with our suppliers evaluating and hand-selecting each diamond for its quality and brilliance. Our gem laboratory or an independant laboratory then inspects every diamond to ensure it meets the strictest quality standards in the industry in carat, cut, colour and clarity. You can be confident your purchase is as special to us as it is to you.

Buying Diamonds at Costco

Each piece of jewellery is thoroughly scrutinized for diamond quality, as well as overall manufacturing and craftsmanship. Costco’s team of Gemologists, all of whom have graduated from a GIA program, inspect for diamond colour, clarity, cut, and carat weight. When purchasing diamond jewellery from Costco, you can be assured you will receive quality jewellery at an unparalleled value.

We guarantee that all diamonds supplied by Costco Wholesale have a clarity to be "VS2" or better and colour to be "I" or better as outlined by the industry standard in the Gemological Institute of America (GIA) grading guide. Costco only sells diamond cut grades that range from Very Good to Excellent.

Although treating diamonds is an accepted practice among many jewellers, Costco sells only natural and untreated diamonds.


All diamond jewellery items from Costco come with some type of certification or documentation. Depending on the characteristics of the item, it may come with one or more of the following reports:

Costco Article of Description

When you purchase an article of jewellery with a diamond of less than 1.00ct, you will receive an Article of Description written by one of our Gemologists, with a degree from GIA, detailing your jewellery piece.

GIA Diamond Grading Report

When you purchase an article of jewellery with a 1.00ct centre diamond or larger, you will receive a Diamond Grading Report from the Gemological Institute of America (GIA) detailing and mapping the diamond.

Jewellery Grading/Gemological Report

When you purchase an article of jewellery with a 1.00ct centre diamond or larger, it will also include a Jewellery Grading/Gemological Report describing the jewellery piece.


The most important characteristic of a diamond is cut, which refers to its basic shape and the quality of its proportions. When evaluating the quality of a cut, the diamonds facets and surfaces are examined to determine how well they reflect light. The more brilliant and luminous the diamond, the better the cut. The grading scale for the cut of a diamond ranges from Poor to Excellent

Diamond Cut Shallow

Cut too shallow light escapes through the bottom.

Diamond Cut Deep

Cut too deep light escapes trough the sides.

Diamond Cut Perfect

Perfectly cut more light, more brilliance on top.


The second most important characteristic of a diamond is colour, which refers to its natural hue. It’s incredibly rare for a natural diamond to be colourless, almost all diamonds have some type of inherent colour, no matter how faint. During inspection, a diamond is assigned a letter to describe its colour grade, these letters range from D (colourless) to Z (pale yellow). The closer a diamond is to being white, or colourless, the higher the value.



Near Colourless

Near Colourless

Slighty Tinted

Slighty Tinted

Very Light Yellow or Brown

Very Light Yellow or Brown

Light Yellow or Brown

Light Yellow or Brown



Most diamonds contain flaws that make them unique. Flaws are considered to be any blemishes or internal inclusions. Since a diamond is a natural stone, flaws are quite common and expected. Most minor flaws are usually not visible to the naked eye, and do not affect the beauty and brilliance of the diamond. The fewer and smaller the inclusions, the rarer the diamond. Each diamond is given a Clarity Grade that ranges from Included to Flawless. The closer a diamond is to Flawless, the higher its value. To determine a diamond's clarity, it is examined under 10 x magnification by a trained eye.


FL - Flawless
IF - Internally flawless with minor surface blemishes


WS1 / WS2
Very Very small inclusions (not visible to the naked eye)

VS1 - VS2

VS1 / VS2
Very small inclusions (not visible to the naked eye)

SH - S12

SH / S12
Small inclusions (not visible to the naked eye)

11 - 12 - 13

11 / 12 / 13
Inclusions (visible to the naked eye)


The weight or size of a diamond is measured in carats (ct.).
One carat = 100 points.
Half carat = 50 points.
Quarter carat = 25 points.
The heavier and larger the diamond, the more rare it usually is.


Diamond Cut Shallow

2 cts.

Diamond Cut Deep

1.75 cts.

Diamond Cut Perfect

1.5 cts.

Diamond Cut Perfect

1.25 cts.

Diamond Cut Perfect

1 cts

Diamond Cut Shallow

0.75 cts.

Diamond Cut Deep

0.50 cts.

Diamond Cut Perfect

0.25 cts.

Diamond Cut Perfect

0.10 cts.

Diamond Cut Perfect

0.05 cts

Diamond Shape

There are 8 standard shapes, or cuts, for diamonds, each with their own unique characteristics. Most people have an opinion on which shape is the most beautiful or valuable, but in the end, the only opinion that matters is yours. Choosing the shape of a diamond is a matter of personal preference.

Six of these cuts are considered Brilliant, and these include: round, princess, oval, cushion, radiant, pear. Brilliant cut diamonds have a larger amount of facets, which are intended to maximize light reflection and brilliance. Their exceptional sparkle is the reason brilliant cut diamonds are so very popular. The emerald and square emerald cuts have larger, wider facets that really showcase the colour and clarity of a diamond. Their particular beauty and appeal lies in their transparency and depth.

Diamond Round


Valued for its exceptional shine, the round brilliant is the most popular shape for diamonds, particularly engagement rings. It gets its intense beauty from its unique multi-faceted cut. Achieving this intricate cut requires more time and expertise, which is reflected in its higher price.

Diamond Princess


With its crisp lines and fiery brilliance, it’s no mystery why the princess diamond is so very popular. This square brilliant shape consists of multiple sparkling facets. Although it may be a classic, the princess cut also has a very contemporary appeal.

Diamond Cushion


The elegant cushion diamond gets its name from its pillowy shape, which is square with gently rounded corners. It has a very luxurious, old world feel to it, which may be why it is sometimes referred to as an old European mine cut. The brilliant cushion cut has large facets that give it wonderful radiance and a very substantial appearance.

Diamond Oval


With its lovely elongated shape, the oval diamond offers a refined, graceful look for a woman’s hand. This special brilliant cut has an extraordinary sparkle and expansive surface area, which gives it a larger appearance than other shapes of the same size.

Diamond Emerald


Nothing compares to the old world glamour of an emerald diamond. Its clean rectangular shape really showcases the diamonds colour and clarity. Unlike other multi-faceted shapes, the appeal of the emerald cut lies in its openness and depth.

Diamond Pear


The pear diamond has a lush teardrop shape that is both dazzling and feminine. This beautifully faceted brilliant cut features one rounded, well-balanced end and one pointed end. It offers a very bold and unique look.

Square Emerald

Square Emerald

The regal square emerald cut is one of the rarest diamond shapes, and it is admired for its ability to showcase a diamond's depth and clarity. It has a lovely square shape with softly rounded corners and large, elegant step-cut facets. Much like the emerald cut, the beauty of the square emerald cut diamond lies in its transparency.

Diamond Radiant


The gorgeous radiant diamond owes its remarkable sparkle to its highly-faceted brilliant cut. Incredibly luminous and fiery, the rectangular radiant is an exquisite blend of the princess and emerald shapes, and is a fashionable choice in engagement jewellery.

Diamond Care & Maintenance

Although diamonds are one of the hardest substances on earth, they are still vulnerable to damage such as abrasion, chipping, and breakage—that’s why it’s important to wear and store your diamond jewellery with care. Avoid all harsh chemicals such as bleach, ammonia, chlorine, hair spray, and perfume, as they may cause permanent damage to diamonds and metals. Avoid direct exposure to dirt, oils, and lotions, which can create a cloudy film on diamonds, as well as settle into the crevices of jewellery mountings. We recommend having your jewellery inspected every 6 months by a qualified jeweller for any needed maintenance or repair.


We recommend having your diamond professionally cleaned and inspected once every six months by a qualified jeweller. This should include checking the mounting for loose stones, prong repair and inspecting the general condition of your jewellery.


To avoid dirty build-up from cosmetics, natural oils, dirt, soap, etc., periodic cleaning is suggested. This will keep the surface of your diamond brilliant and shiny. You can use professional or home-made cleaner. Diamond Cleaning Solution: 1 part ammonia to 6 parts water; gently hand-scrub with a soft-bristle brush.


Accidents do happen and we strongly recommend that you insure your diamond against loss, theft, and damage.