Learning and understand the 4Cs, which essentially outlines a diamond's quality, is paramount in the purchase of a diamond.
GIA (The Gemological Institute of America)
certification is the benchmark of the industry. They have set their standards of diamond grading so high that they have become the largest and most respected nonprofit institute of gemological research and learning. GIA is responsible for the 4Cs of a diamond which includes:
Usually people think of diamonds as white (D-F colors) or near colorless (H-J), but of course there are diamonds of every color including pink, blue and yellow. In white diamonds, though, it’s the absence of body color that makes the stone more valuable.
On the D-Z white diamond grade scale (colored diamonds are graded on a separate color scale), the letter D is the highest, given to those very rare diamonds that are completely colorless. If you compare this stone to just about any other diamond, the Letter-D diamond will be visibly whiter.
At the other end of the spectrum is the letter L. Although antique diamonds with this rating have a tint of yellow that is easy to see, they are still considered white diamonds. Letter-L diamonds are less expensive than diamonds with higher color ratings, which means that improvements in clarity and cut and setting may be affordable. Another tip worth noting is that a Letter-L diamond with blue fluorescence can counter-balance the yellow tint, making the diamond appear whiter.
It might make your color rating selection decision easier to remember that most people can’t tell the difference between diamonds graded G through I, since all stones with those ratings are virtually colorless to the untrained eye. The lower price, on the other hand, can be appreciated by anyone.
Another thought to keep in mind is that diamonds at the lower end of the color scale can be said to have a warmer glow than colorless stones. This is very subjective, of course, but if you prefer the look of lower-color diamonds, you may be able to afford a larger stone and still stay within budget.
As a rule of thumb, yellow gold settings show lower color grade stones off to their best advantage. If you plan to set your diamond in white gold or platinum, however, it’s probably advisable to choose a higher color grade diamond.
GIA’s color-grading scale for diamonds is the industry standard. The scale begins with the letter D, representing colorless, and continues with increasing presence of color to the letter Z, or light yellow or brown. Each letter grade has a clearly defined range of color appearance. Diamonds are color-graded by comparing them to stones of known color under controlled lighting and precise viewing conditions.
Cut is the factor that fuels a diamond’s fire, sparkle and brilliance.
Cut refers mainly to a diamond's proportions, although symmetry and polish are also taken into account, but not to the gem’s actual shape. This is because proportion determines a diamond’s brilliance.
Every diamond starts by being cut from its rough crystal state and its final appearance depends on the quality of that cut. If done well, the stone will be brilliant and reflect a lot of light. A diamond with an excellent cut is a much brighter stone than one with a poor cut.
Cuts are graded from excellent to poor and the proportion of the cut is crucial to its rating. When a diamond is rated at the top end of the scale, it means that its proportions allow nearly all incoming light to reflect, giving the stone fire, brilliance and sparkle.
Whether the diamond is deep-cut, with a smaller top (table) and larger depth, or shallow-cut, with a relatively smaller depth compared to its larger table, it’s the proportions of the cut that will ultimately determine how much light is returned to the outside.
It makes sense that cuts graded either excellent or very good are quite similar in respect to the amount of reflection, brilliance and fire. That being said, however, diamonds with very good cuts tend to be less expensive than those graded as excellent.
You’ll save more significantly when purchasing stones with good or fair cuts, while still enjoying moderate brilliance and fire. Most people will only really notice the difference if a fair cut diamond is compared directly with an excellent cut diamond.
The clarity of a diamond is graded based on the number of inclusions within it, as well as any outer blemishes. Clarity grades range from F (“flawless”) to varying levels of I (“included”), and that means for diamonds an F clarity grade is actually the best possible (though for diamonds F’s are extremely rare).
Inclusions are caused by small fractures or particles within a diamond, and the more inclusions a diamond has, the lower its clarity grade is. Many diamonds have inclusions that can only be detected with a powerful microscope, but if there are multiple inclusions, or large visible ones, that’s when the ability of the diamond to reflect light, and therefore its clarity, is affected.
A diamond absolutely does not need to have a flawless grade to be worth buying. In fact, since most people can’t detect blemishes or inclusions in diamonds, most lower grade clarity diamonds (like Very Slightly Included or Slightly Included) function as beautiful, affordable diamonds. You only need to worry if you’re considering buying diamonds with Included clarity grades. This level of imperfection is often very visible and such inclusions are noticeable even to the average viewer.
Here’s a guide to the specifics of what different clarity grades indicate. For the levels with numbered subcategories, keep in mind that 1 indicates a higher clarity grade, and 3 the lowest.
Flawless (F) – no inclusions or blemishes
Internally Flawless (IF) – no inclusions internally, but contains small surface blemishes
Very Very Slightly Included (VVS1-VVS2) – tiny inclusions small enough to make it difficult for even a skilled diamond grade to detect under 10x magnification.
Very Slightly Included (VS1-VS2) – Has small inclusions that are somewhat easy for a grader to detect under 10x magnification.
Slightly Included (SI1-SI2) – Has small inclusions that graders can easily see with 10x magnification.
Included (I1, I2, I3) – Has inclusions extremely visible under 10x magnification, and often they are visible to the naked, untrained eye.
Because diamonds formed deep within the earth, under extreme heat and pressure, they often contain unique birthmarks, either internal (inclusions) or external (blemishes).
The GIA Clarity Scale contains 11 grades, with most diamonds falling into the VS (very slightly included) or SI (slightly included) categories. In determining a clarity grade, the GIA system considers the size, nature, position, color or relief, and quantity of clarity characteristics visible under 10× magnification.
A carat is the basic unit used to measure the weight of a diamond (not to be confused with karat, which measures the purity of gold). One carat has an equivalent weight to 0.2 grams, 200 milligrams or 0.007 ounces, but since diamonds are usually dealt with in very small amounts, the smallness of the carat-unit makes numbered measurements easier (because the numbers have fewer decimals).
In general, the more carats a diamond weighs, the larger it appears, but this is certainly not always the case. Sometimes diamonds are purposefully cut very shallow. That means that a smaller carat diamond is made to be very wide, therefore appearing to be much larger than it actually is. However, diamonds cut in this manner are not ideal, because when a stone has a shallow cut, the brilliance and light reflection are severely diminished. For a diamond that has the best brilliance, you want to be sure to take the cut (with appropriately proportional width and length measurements) into consideration.
In addition to the carat, there is another unit that’s often used to measure diamonds, called a “point.” One carat consists of a hundred points, so this means smaller diamonds are frequently measured in terms points. For example, a diamond that weighs 0.5 carats can also be said to weigh 50 points.
Vintage 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.)