Cut

When a diamond is cut with ideal proportions (for its shape), more light reflects out the top of the gem
producing incredible fire and brilliance.
A poorly cut diamond, on the other hand, looks dull and lifeless because incongruous proportions allow light to escape out the bottom and sides.
In short, a well-cut diamond will be much more brilliant because it reflects and refracts light better than one not cut as well. A better cut is more rare, more desirable, and therefore, will command a higher price.

Color

White diamonds are not all colorless. The spectrum ranges from totally colorless to light yellow. A lettering system from D to Z is used to identify the amount of color present in each diamond, with D awarded only to the rarest, totally colorless diamonds. Diamonds graded D, E or F are considered colorless. Diamonds graded G, H, I or J are considered near colorless. The color will intensify further down the scale. The more colorless a diamond, the more rare it is, therefore, more valuable.

Clarity

Natural diamonds are formed by tremendous heat and pressure deep within the earth. This process can result in “inclusions” and “blemishes.” These are simply fancy words for imperfections either in, or on, the diamond.
No diamond is perfect, but the closer it comes to being flawless the higher its value. Minor inclusions seldom affect a diamond’s beauty, although if heavily flawed, it will affect the price.

Carat Weight

Carat weight refers to size and weight of the diamond. Larger diamonds are more scarce than smaller diamonds, and therefore, more valuable. However, two diamonds with the same carat weight, can vary greatly in price depending on the color, clarity and most importantly, cut.
A smaller diamond with excellent color and clarity may cost more than a larger diamond with lower color and clarity.
It is simply a matter of deciding what matters most to you, size or quality. It is wise to find the best combination of size, color and clarity to suit your budget.