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).
Gia Certified Loose Diamonds
GIA certified loose diamonds are diamonds that have been certified by the Gemological Institute of America. They are widely considered the best and most consistent and most respected certifiers of diamonds in the world.
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The GIA is a not-for-profit organisation that sets out to maintain a high level of standards and professionalism in the diamond industry. They do a large number of activities, but of most interest to consumers are the GIA certificates that come with some diamonds.
A GIA diamond grading report provides an assessment of the four key characteristics of the diamond - cut, clarity, colour and carat weight. Because the GIA is so consistent you can use these reports to compare different diamonds. However even to diamonds graded with the same clarity by the GIA can look quite different to the naked eye so it is worth looking at the individual diamonds either in person or using a photo.
You can buy GIA certified loose diamonds through many of the major online retailers such as James Allen and Blue Nile. If you are interested in only GIA certified loose diamonds, most of the online diamond search tools have a tick box which you can tick to search only for these types of diamonds.
When you're shopping in bricks and mortar stores, you can ask the staff whether they have any GIA certified loose diamonds in their store, or whether they can order in any.
Some people will try to convince you that the certifying body doesn't matter, but this is flatly not true. While some of the other certifying bodies are okay, you need to do your research to find out exactly what a certain rating is equivalent to in another certification.
For example, a diamond that is rated a H colour by the GIA may be rated as an I colour by another certifying body. Make sure you do your research first if you're buying a non-GIA certified loose diamonds.