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Generally speaking 'the larger the stone the greater the price per carat'. The reason for this is that larger stones, particularly of good quality become rarer and more difficult to source. You may also note from your searching that a premium is paid for stones that are 1 carat or more in weight. This is a market characteristic which is a simple case of 'supply and demand'. You may often find that diamonds just under the carat mark (0.90 - 0.99) are considerably cheaper than a whole carat but look almost identical in size!
F - Internally flawless - Has no inclusions when examined by an experienced grader using 10 X magnification.
VVS1 - VVS2 - Contains minor inclusions that are difficult for even experienced graders to see under 10 X magnification.
VS1 - VS2 - Contains minute inclusions when observed with effort under 10 X magnification.
SI1 - SI2 - Contains inclusions that are noticeable to an experienced grader under 10 X magnification, although still not visible to the naked eye.
The 4 Cs
Colour - Clarity - Cut - Carat weight
So why certified stones and why the GIA?
Can you tell the difference between a diamond and a cubic zircona? Or even a colour 'D' stone and a colour 'F' stone? The difference could be hundreds or thousands of pounds - your pounds.
Diamond grading is a science
There are two types of certificate, laboratory and non-laboratory.
If the certificate is from an independent gemologist (and not a laboratory) there can be a degree of subjectivity in the grading. If the certificate has come from a laboratory this means that the diamond has been subjected to scientific tests that are measured objectively. Even laboratory grading can vary slightly, however, industry opinions are that the GIA laboratory is the best.
The 4Cs categories were largely established by the GIA, the method by which all diamonds are now graded. A diamond with a GIA Diamond Grading Report can be valued at up to 15% more than a non-certified stone.
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