This is another important thing to look for when buying the perfect diamond, as it can also have an effect on a diamond’s value. Diamonds can have internal characteristics, also known as inclusions, as well as external characteristics that are known as blemishes. A flawless diamond, one that has neither inclusions nor blemishes, is very rare. When a grader looks at clarity, he uses magnification and specific lighting and determines the diamond’s clarity grade based on the particular characteristics he sees.