Clarity refers to how clean or clear the diamond is with respect to natural microscopic characteristics that were trapped within or on the diamond while it was forming. The clarity grade is the degree to which the diamond is free of inclusions (internal) and blemishes (external). Inclusions may be crystals of a foreign material or structural imperfections such as tiny cracks, known as feathers, which can appear whitish or cloudy. Experienced graders use 10X magnification to identify the various clarity characteristics, and to map their location on "diamond plots." These plots are like small maps for each individual diamond, and are used to identify each individual stone. No two diamonds will ever have the same internal pattern, and the plots work as a form of individual identification much like a fingerprint. Gemologists consider the quantity, size, color, location, orientation, and visibility of inclusions in determining the clarity grade of a diamond.