The Four Cs -
To determine a diamond's value, experts use the Four Cs—cut, color, clarity, and carat weight.
When people think of cut, they often think it’s the shape of the diamond. But, it’s about how light is returned due to a diamond’s facets. Cut is responsible for brilliance, fire, and scintillation of a diamond.
A diamond’s color is measured using the GIA® D-to-Z diamond color grading system. This system is the most widely accepted for grading. All diamonds are evaluated based on the absence of color.
Just as a diamond’s color is graded on the absence of color, the diamond’s clarity is graded on the absence of inclusions and blemishes.
Internal characteristics = Inclusions
External characteristics = blemishes
In addition to color, cut, and clarity, carat weight directly correlates to price of the diamond. This happens because the supply is low (larger = rarer) and demand is high (larger = more popular).
Now, Lab-Grown or Natural Diamond.
What's the difference?
Lab grown diamonds are a real diamond at an attractive price. They are becoming more and more popular. When you put a lab grown diamond next to a naturally grown diamond you can not tell the difference. Lab grown diamonds have the same physical, chemical, and optical properties as a natural diamond. The only difference is the origin which takes a highly specialized piece of equipment to test it.