The Sidney Thomas Diamond Guide


Throughout history the diamond has dazzled men and women alike more than any other gemstone. Kings and queens wore diamond crowns, and knights decorated their armor with uncut diamonds. Once believed to have magical powers, the diamond gave the wearer strength. It was a symbol of fearlessness and fortune.


Today, the diamond is an international emblem of love, present in many engagement rings and wedding bands. The radiance of a diamond is extraordinarily captivating, making it a choice gemstone for necklaces, bracelets and earrings, as well.

There are factors to consider when selecting diamond jewelry, often referred to as the "4C's": color, clarity, cut and carat weight. The discussion below will provide valuable information about these criteria. Buying a diamond is a very personal decision. That being said, it is up to you to decide which combination of the 4C's makes up the ideal diamond for you.



Carat weight is fairly straightforward. Diamonds are weighed in carats, which are made up of 100 points. For example, a three-quarter-carat stone is 0.75 carats or 75 points. The supply of high-carat diamonds is limited, therefore, as the weight of a gemstone increases so does its value. However, carat weight refers to the weight of a diamond, not the size. In other words, two differently-shaped gemstones of the same carat weight can have different dimensions and one can look larger than the other.


Most diamonds contain inclusions, or very tiny natural characteristics. Surface blemishes can also exist. A trained gemologist determines the clarity of a diamond by using 10x magnification. The size, number, position, type and color of these inclusions determines a diamond's clarity grade. Color is important because dark inclusions detract from the gemstone's beauty more than gray or white. The smaller and fewer inclusions, the more valuable the diamond. The most well-known clarity grading scale is through the Gemological Institute of America (GIA). Here is how diamond clarity is graded:

Flawless: No inclusions or blemishes under 10x magnification
IF: Internally flawless with surface blemishes
VVS1 – VVS2: Very, very slightly included; inclusions are minute
VS1-VS 2: Very slightly included; inclusions are minor
SI1-S1 2: Slightly included: inclusions are noticeable
I1, I 2, I 3: included; inclusions are observable


FL : Internally Flawless FL  IF

VVS1 VVS22 : Very, Very Slight Inclusions VVS1  VVS22
Very, Very

VS1 VS22 : Very Slight Inclusions VS1  VS22

SI1 SI2 : Slight Inclusions SI1  SI2

I1 I2 I3 : Eye Visual Inclusions I1  I2  I3
Eye Visual



White diamonds are graded on their lack of color. The GIA's diamond color grading scale has a range from D to Z. D is colorless while Z is highly colored, usually tinted yellow. D, E and F graded diamonds are considered colorless. G, H, I and J are considered near-colorless as color is unnoticeable to the untrained eye. In general, the more colorless a diamond is, the higher its value.


Diamond Color D-F Colorless D–F

Diamond Color G-J Near Colorless G–J

Diamond Color K-M Slightly Tinted K–M

Diamond Color N-R Very Light Yellow or Brown N–R
Light Yellow
or Brown

Diamond Color S-Z Light Yellow or Brown S–Z
Light Yellow
or Brown


Fancy Diamonds

Natural colored diamonds such as yellow, pink and brown are referred to as "fancy diamonds" and are not graded using the GIA scale, since they are prized for their color.


Cut is often confused with diamond shape. Diamond shape refers to the appearance of a diamond. Round, pear, princess are all examples of diamond shape. Cut determines a diamond's reflective qualities, also known as, sparkle, fire or brilliance. The better a diamond is cut, the better its brilliance, and the higher its value.

Diamond cut affects the way light enters a diamond. A well-cut diamond will reflect more light on the top of the gemstone, resulting in a more brilliance. With a poorly-cut diamond, light will escape through the bottom or sides and the gemstone will have less sparkle.

Cut Too Shallow
Light escapes
through the bottom

Cut Too Deep
Light escapes
through the sides

Perfectly Cut
More light, more
brilliance on top



Although diamonds are the hardest substance, they do need care. For diamonds that are worn daily, wash with jewelry cleaner and dry with a lint-free cloth weekly. Brushes can damage the mounting, so use them sparingly. Avoid wearing a diamond in swimming pools as chlorine can harm a gold mounting. Sidney Thomas recommends that a diamond be inspected and cleaned periodically by a trusted jeweler. This service is always complimentary if you purchase your diamond ring at Sidney Thomas.


When choosing a diamond, be sure to review its diamond certificate, which guarantees the quality of the gemstone. It is a grading report from a diamond lab which details the characteristics of a diamond, including the 4C's.

Diamond Shapes

Sidney Thomas carries a range of diamond shapes including round, princess, pear, cushion, oval, emerald, marquise and radiant.


Conflict Diamonds

As one of America's foremost fine jewelers, Sidney Thomas shares the concern of all regarding conflict diamonds. We support the Kimberly Process and purchase diamonds only through legitimate dealers in open transactions. We will only source through legal and established diamond dealers. As part of our purchasing process, we buy diamonds from manufacturers who have documentation verifying that the merchandise was obtained through legitimate channels. Additionally, the US Customs Service is actively enforcing the Kimberley Process requirements as diamonds enter American ports.

Lab-Grown Diamonds

Learn more about Lab-Grown Diamonds