The key to buying a diamond is a combination of having technical knowledge, being market savvy and most importantly, developing an “eye”. The most important rule to remember is that the right diamond should jump out at you from the moment you see it. In the diamond industry, all diamonds are graded according to the 4-Cs. Understanding the 4-Cs and the diamond industry will allow one to become a savvy diamond buyer.
Of the 4-Cs, clarity is the hardest to determine by the average consumer and one of the reasons to buy from a trusted jeweller. Grading starts at IF (internally flawless), followed by VVS1 and VVS2 (Very very slightly included). These two grades are very uncommon and for the money, isn't a good value to buy a stone in. You can never differentiate a diamond between VVS1 and VS1 even under 100X magnification. The price difference could be thousands of dollars. People who want the best quality and value usually buy in the VS1 or VS2 level. SI-1 and SI-2 are the next level. SI stands for slightly included with SI-1 being clearer than an SI-2 stone. If you see a stone that's a lot of inclusions under a microscope but isn't visible to a naked eye, this is an SI-2 stone. Any stone that's flaws visible to a naked eye will be an SI-3 or sometimes labelled as an I-1 stone. The rapport will grade these stones down to an I-3. These are usually the stones that are advertised for $399 a carat. For engagement ring quality diamonds, it's recommended not to go below an SI-2.
Of the 4cs, Colour is the most visible to the buyer. The colour chart starts at D, with D/E/F being the most pure and the most white of all the diamond colours. The second category is G/H/I, which is considered the near colourless category and will have a varying hint of colour. When the majority of the diamonds were formed, gaseous elements such as nitrogen were trapped in the carbon lattice thus causing variation in the diamond colours. Within the J/K/L range, the buyer will be able to see varying degrees of yellow in the stones. Although colour is graded down to Z, the rap sheet stops at M. For engagement ring quality, anything below the colour “I”. isn't recommended. The lower colour stones are usually made for other purposes.
Because the prices for colour do vary greatly, it's imperative for the buyer to be able to differentiate between the colours. The only way to truly grade the colour is to compare the stones upside down, against a white background and compare it to a master set of stones. For example, to see an E color stone, it must be compared against a D and an F stone. it's impossible to see colour set in a mounting and empirically state the exact colour. For people who want the best value and quality, buying a G colour stone is ideal. A G colour stone is noticeably whiter then the H. it's priced in the near colour-less category of stones, where the savings will be greater. To go with a high colour and lower clarity combination, such as an E colour but good SI-2 clarity will also yield a good value.
Carats or the weight of the diamond is the 3rd determinant of price. 100 points equal a carat. Is impossible for human eye to see. Though a diamond can be 1 carat in weight, it can look bigger or smaller than its carat weight states. So when buying a round diamond of 1 Carat size, look for stones that are at least 6.2mm in diameter. Also, because the jewellery industry has a tolerance level of 5% difference on stated carat weights on jewellery, this is why buying from a trusted jeweller is key. it's impossible for any one to eyeball carat size, you can't tell the difference between a 1 CT tennis bracelet or a .90CT bracelet. There is a big price differential.
Cut is the most technical of the 4-C’s. The fact of the matter is that one can see a diamond that's cut well versus one that's cut poorly. The cut states that the crown (top of the diamond), pavillion (bottom of the diamond) and the girdle (thin middle ring that divides the crown and pavillion) should've ideal range that the diamond should be cut.
The last C is the certs that diamonds carry and is the final component that affects diamond pricing. Many stones that are above .75CT are certified by independent laboratories. The certificates will plot a mapping of the inclusions, give dimensions and measurements of the diamond, state the polish and symmetry, fluorescence. State if a diamond has been enhanced. Although there are many labs that certify diamonds, the most popular on the market are certified by GIA or EGL. GIA (Gemological institute of America) has predominately been very strict or rather on the conservative side of their grading. GIA diamonds tend to sell at a premium. EGL (European Gemological Laboratory) is also very popular but sometimes have struggled with their consistency. Thus their stones will usually sell 5 –. 10% less then a stone with the same grade from GIA. GIA stones aren't necessarily better stones then EGL certified stones. Plenty of beautiful stones get sent in to be processed by EGL as they do GIA.
The price difference for clarity and colour affects the prices exponentially. Buying a high colour is where the buyer’s dollar will be well spent. Clarity is impossible to see without a microscope but a diamond of high colour can be seen from across the room. If there are two diamonds that have the same level of quality, acceptable price points and even the same grading from the laboratories, then let your eye be the final judge. After all, you're ultimately buying a diamond for its beauty and sentimentality. While only considering the technical jargon, let your heart be the final judge.