Emerald is believed to protect against evil, and is also known as the stone of successful love. Emerald's hue, tone, and saturation determine its value, and the most desirable emerald colors are bluish-green to pure green with strong to vivid color saturation and medium to dark tone. "Eye clean" emeralds are very rare. Colombia produces the highest quality and the best volume of emeralds. Some emeralds are treated with oils and or resins to make inclusions less visible and improve the color.