Radiant Cut

Radiants show color quite strongly, so it's recommended not to go too low on the color scale. The choice of color also depends on a setting:

	Solitaire	Small side-stones	Substantial side-stones
White gold/Platinum	H+	G+	same as side-stones+
Yellow gold	J+	I+	same as side-stones+
		e.g. pave setting	e.g. three-stone setting

Radiants are quite forgiving of inclusions, so you can go relatively low on a clarity scale, as long as the diamond is eye-clean. SI1, SI2 clarity or higher is recommended.

Note: You can always go lower in clarity, but it's going to get increasingly difficult to find an eye-clean Radiant below the minimum recommended SI2 grade.

For best value, go with the lowest clarity possible that is still eye-clean. If a diamond is eye-clean, then it doesn't really matter, if it's flawless or SI2. It will look the same, provided all other characteristics are the same.

Professional and unbiased assessment of a diamond's characteristics is stated on a diamond grading report, commonly referred to as a certificate. Certificate, while not 100% reliable, is essential in determining a diamond's value.

The standard for diamond grading is pretty much set by GIA - Gemological Institute of America. They are the most reputable and consistent lab in the industry. AGS (American Gemological Society) is not far behind.

If a diamond is not certified by GIA or AGS, you can be pretty much certain that you are looking at lesser quality than indicated. This puts you in a bad position of not knowing the true diamond characteristics, which almost always results in overpaying. That is why a certificate from a well-respected grading lab is so important.

Blue fluorescence can have a positive, negative, or zero effect on a diamond. Diamonds in the lower color range (H or lower) can benefit from it, as it can make them look whiter, more colorless. On the other hand, strong fluorescence can cause a stone (especially in the higher color range D-G) to appear hazy or milky under certain light conditions. One of the biggest benefits of fluorescent diamonds is that they generally cost less.

GIA grades fluorescence as None, Faint, Medium, Strong, and Very Strong.

Faint fluorescence will have zero effect on color and overall appearance. Fluorescence of this type is not an issue and shouldn't be a purchasing factor.

Medium fluorescence will in most cases have zero to very small influence on color and overall appearance, however, colorless diamonds can sometimes exhibit negative effects and should be examined in different light conditions before purchasing.

Strong/Very Strong fluorescence requires caution. Generally, it's not a good idea to buy a colorless diamond with Strong/Very Strong fluorescence. As for lower color diamonds, even they can sometimes look hazy with strong fluorescence, so never buy a stone with this type of fluorescence without careful visual inspection.

The problem with diamond grading labs other than GIA or AGS is that they are looser and more inconsistent in their grading standards. A GIA color H is an IGI color G and an EGL/HRD color F. The same goes for clarity.

While it's true that IGI, EGL, and HRD diamonds are sold at a discount, you can be certain that the same stones would cost less, if they would be certified by GIA or AGS. Why? Because they would get lower grades and thus lower price. Lower than discounted IGI, EGL, and HRD stones with higher grades.

Diamond merchants use IGI, EGL, HRD, and alike to maximize their profits. They know they can sell diamonds with inflated grades for more, even if they're sold at a substantial discounts. Some merchants also use their in-house certification, usually for the sole purpose of increasing their profits. These kinds of certificates are meaningless.