CUT refers to the overall shape (round, oval, princess cut, etc.) and also to the mathematical nature of the proportions and symmetry. For round diamonds, there is an 'ideal' cut, which is dependent on the exact angles and percentages of different parts of the diamond relative to one another. It's these angles and proportions that determine how much of the light entering the diamond from the top is refracted back to the eye--that's what makes diamonds sparkle!
A point of interest: The first "ideal" cut for a diamond was discovered in the 1950s by a fellow named Tolkowsky. It is still often referred to as a Tolkowsky cut. Other mathematical models have produced different "ideals" for diamonds, but ultimately, a diamond will need to resonate with YOU to be chosen.
Based upon the physics and angles of light traveling through diamonds, the light is refracted (bent) at a specific angle upon entering the surface, then reflected off the back facets, then refracted again as it travels back to the surface of the diamond and eventually makes it back to your eye. Lots of complex angles and facets to take into consideration.
When considering the purchase of a round diamond, I suggest comparing an ideal or premium (close to ideal) cut diamond to any other diamond you are considering. Most often you will see a slight increase in the sparkle factor although you will also pay a bit more for that too because there is usually more weight lost to achieve the ideal proportions. So all other factors being equal, the price per carat will be a bit higher for an ideal cut.
Meanwhile, before the "ideal" cut was used, a number of older cuts including the mine cut, the European cut, and the transition cut were used to beautiful result. Many prefer these older diamond cuts, as they can produce greater flashes of color across their surfaces. Again, the right diamond for you will be a very personal decision.
Note: In other diamond shapes, such as oval, pear, emerald cut, princess, etc. there are no universally accepted standards for an 'ideal' cut in those shapes. However, the GIA does grade these stones for polish and symmetry and a well cut stone will be visually appealing.
COLOR more correctly refers to the absence of color. The color grading system that is now universally used throughout the world was originally developed by the Gemological Institute Of America several decades ago. They created the "4 C's" to put an end to the confusion of every major diamond house using its own proprietary grading system and thus confusing jewelers and consumers alike.
Because diamonds are so valuable, it’s essential to have a universal grading system for comparing their quality. In the 1940s and ’50s, GIA developed the 4Cs and the GIA International Diamond Grading System™ to objectively compare and evaluate diamonds.
Note: the GIA maintains an excellent educational website at gia.edu. Highly recommended to learn tons of stuff about diamonds and how they are graded and evaluated.
Also highly recommended: Get their free app there, GIA 4Cs Guide. For iPhone or iPad. Here's the link: https://itunes.apple.com/us/app/gia-4cs-guide/id469023195?mt=8
Now everyone is 'on the same page.' The color grade for a diamond starts with the letter "D" and continues down the alphabet all the way to "Z." The grades D, E, and F are considered 'colorless'. The grades G, H, I, and J are considered 'near colorless', K, L, M, are called 'faint', and so on down the line …
CLARITY grading in diamonds was also established by the GIA. Clarity grading is conducted under 10X magnification for the top eight grades ranging from 'flawless' (FL) down to 'slightly included' (SI). Lower grades, where some inclusions are visible to the 'naked' eye (without magnification) are labelled "I" grade, meaning 'included' and accompanied by a number 1, 2, 3, etc. depending on how many inclusions, or flaws, and how visible they are.
The diamond jewelry we create at Uniquely Yours tends to have very high color and clarity graded diamonds, which isn't something you'll find in "mall" jewelry.
Again, I would refer you to the excellent information available at the GIA website or in their app.
CARAT refers to the weight of the diamond.
Diamonds and other gemstones are weighed in metric carats: one carat is equal to 0.2 grams, about the same weight as a paperclip. (Don’t confuse carat with karat, as in “18K gold,” which refers to gold purity.)