Clarity is the internal quality of a diamond. The term refers to the degree which a diamond is free of interior or exterior birthmarks or inclusions. An inclusion being any internal characteristic apparent to a trained or professional eye at 10x magnification. The size, position, and type of birthmarks affect the value of a stone according to the degree to which it interferes with the passage of light through the diamond. Using such words as "flaw" or "imperfection" with a diamond customer is misleading. These terms imply that the diamond has no value. Only the most rare of diamonds are free from "blemishes". Birthmarks, or natures fingerprints are terms developed to indicate the presence of these blemishes without the negative implication. While minute inclusions reduce the cost of a diamond, they do not mar its beauty or endanger its durability.