Usually, when it comes to buying a diamond, most guides will explain the 4 Cs involved. Carat, Cut, Colour and Clarity.
Carat
Firstly, the carat is simply the weight of a diamond. One carat is equivalent to 0.2 g of diamond. Although the carat is the most commonly referred to feature of a diamond, is it actually the least important feature among the four Cs. Unfortunately, the price of a diamond is most influence by its weight. In reality, one should first consider the other qualities of a diamond before then selecting diamonds based on their weight.
A large diamond with high amounts of impurity will be less appealing than a smaller diamond will good colour and clarity.
Cut
Of the 4 Cs, only the cut of the diamond can be determined by man. The cut strives to allow the most amount of light to enter the diamond and reflect back out of it to create the sparkle unique to each diamond. The cut is a test of skill of the craftsman that performs it. If the cut is too deep or too shallow, less light will reflect through the diamond, resulting in a less brilliant appearance.
There are many types of cuts out there, princess, pear, oval, round, heart and many more. If a diamond is well cut, it should glow like fire regardless of the type of cut. The type of cut is more of a personal preference and also depends on the setting you like to have on your ring band.
Understandably, a well-cut diamond will be more valuable than one of the same carat, clarity, and colour but poorly cut.
Colour
The colour of diamonds commonly varies from colourless to many shades of yellow. Typically, the more colourless the diamond, the rarer and thus more valuable it will be. Colour in a diamond occurs due to the fact that different types of gases were trapped within it during its formation. Some diamonds also come in green or blue (a very famous blue diamond is the Hope diamond), and these diamonds are exceedingly rare and extremely precious.
The colour of a diamond is rated using alphabets. Colourless diamonds are usually denoted D, E, or F, with D being the highest quality, followed by E and F. G, H, and I are the nearly colourless to white diamonds. J, K, L, and M are yellow diamonds that range in colour from palest to strongest yellow.
Yellow coloured diamonds are commonly mounted on gold ring bands to hide their yellowish hue.
Clarity
Clarity refers to the impurities or inclusions inside a diamond. Clarity is rated according to the most common scale as shown below.
F – Flawless, perfect clarity
IF – Internally flawless, meaning perfect on the inside, but with minor blemishes on the outside
VVS1, VVS2 – Very very small inclusions that can only be seen under greater than 10 x magnification. Both VVS1 and VVS2 inclusions are invisible to the naked eye, but with VVS2 more visible as compared to VVS1.
VS1, VS2 – Very small inclusions. VS inclusions are also invisible to the naked eye and barely visible under magnification. VS2 inclusions are more visible than VS1.
SI1, SI2, SI3 – Small inclusions that cannot be seen by the naked eye, but readily observed with magnification. The visibility is greater with increasing number.
I1, I2, I3 – Inclusions visible to the naked eye, again visibility is greater with increasing number.
Few people are lucky enough to ever own a flawless or internally flawless or even VVS diamond. Most people wear diamonds with clarity grades of VS or S since most people are only concern with having the inclusions being invisible to the naked eye.
In fact, it may be advantageous to buy diamonds of clarity grade I1 or I2 is the inclusions could be properly hidden from view by its setting. In this way, you could possibly buy a larger diamond at a lower cost.
Read about the other 2 C's of Diamond Wedding Bands.