Quick and Easy Buying Guide
Carat weight: 1 carat = 200 milligrams = 6.5 mm diameter. Doubling weight doesn't double diameter.
Diamond clarity: FL/IF/VVS/VS = super expensive, near perfect. SI = best value if you can check a photo for obvious inclusions (defects).
Color: D-G = colorless, expensive, only if you have money to burn. H-J = best value. Can go lower in gold metal settings than white metal.
Cut: Better cut ratings let more light into a diamond, making it sparkle more. Very important property, don't skimp here.
Set a budget and minimum cut (Premium). Go J color for gold and I/H for white metals. Go searching for SI1/SI2 clarity diamonds at James Allen. Pick a diamond with small/no inclusions. Choose a ring setting and buy it risk-free (60-day returns).
1.38 Carat Diamonds
Diamond carats, points and normal units of milligrams can all be converted between - this 1.38 carat diamond for example weighs 276 mg. What many people don't realise is that a 7.28 mm wide diamond can be a range of weights, not just exactly 5 carats, because the diamond can vary in depth.
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Some online retailers provide, amongst other diamond properties, a property called the cost per carat, which gives consumers another way of thinking about the value of a diamond. Girdle thickness is a diamond property which many people never even think about, but which can critically affect how big the diamond appears to be.
God forbid that this should be a problem for anyone, but it may be that the diamond, once it actually put on the fiance's hand, may appear to be too big and unwieldy. Make sure to take this into account when you're shopping around.
Depending on personal preference, people may choose to get a smaller diamond in order to get a higher colour grade, such as d, e or f. It's heartening to know (if you're a billionaire) that there are actually very large diamonds which are colourless, such as the centenary diamond, which is a grade d colour diamond that comes in at the whopping weight of 273 carats.
People say the four cs for a reason - diamond carat size is just one of the four cs and the others are arguably just as important in determining how 'attractive' and 'good' a diamond is.
I prefer liberty to chains of diamonds. Mary Montagu .