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This is usually seen as one of the most important characteristics for ladies but it is also one of the least understood factors. And, believe it or not, it is actually the least important characteristic when evaluating a diamond’s beauty. Intertrade Associates’ recent survey found that 84 per cent of respondents would prefer a smaller diamond ring if it was of a higher quality.

This was in line with further questioning that showed that 86 per cent didn’t want a showy engagement ring at the expense of quality. Carat weight refers to the actual weight of the stone (one carat= 0.2 grams) and this doesn’t always relate to the physical size or diameter you see. As a diamond increases in weight, it also increases in volume in every direction. So some of the increase or decrease in diamond weight will be seen in the diameter and some will be in the depth. If the stone is poorly cut, it will have more of the weight in the depth and so have a smaller diameter.

Xennox - Carat Weight Explained

For example, a poorly or averagely cut one-carat diamond can have the same diameter as a 0.90ct perfectly cut diamond. Not only will the one-carat diamond look the same size as the perfectly cut 0.90ct diamond, but it will also sparkle significantly less. Ultimately, the larger stone has lost its brilliance because light is being lost through the back of the stone. This situation is quite common for discount and chain stores, because they think clients will only focus on the weight of the diamond and not its diameter (or physical size). Always choose a diamond that has the correct diameter for its weight. A 1.00ct diamond, for example, should measure 6.5mm in diameter, and a 0.50ct diamond should measure 5.1mm in diameter.
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It is always better to go for a slightly smaller, more perfectly cut, diamond, over one that just weighs more. The diamond with the better cut will give you many more years of enjoyment and compliments as it sparkles from across the room. The second reason carat size should be the least important factor on the shopping list is that, as I mention in chapter 6, diamonds are not priced like the tax system, where every dollar over a certain amount is charged at a higher rate. With diamonds, once you hit certain key points like the 1ct mark, a bigger than expected jump occurs, as the whole weight of the stone is charged at the higher rate. Why is this great to know? If you drop in just under one of these price barriers, the price could be significantly less, even though the difference in the diameter may only a few tenths of a millimetre smaller. This leaves either more money in your pocket for the proposal or more money that you can use to put into the cut or colour quality (the things you can see with your eyes). The difference in size between a 0.90ct and a 1.00ct, for example, is 0.3mm, but the difference could be between $1500 and $2000.

Does ten points make a difference in the size?

Yes and no. The answer really depends on the size of the diamond you’re talking about. Under a carat, ten points is usually a noticeable difference. However, between one carat and two carats, there usually needs to be at least a 20-point difference to justify the extra expense. Once you get to two carats, the difference required jumps to 50 points or 1 carat. Once over three carats, clients jump to five carats – which is why a four-carat diamond is not as common as the five-carat size.

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