0.65–0.75 carat (200–225 milligrams) is the maximum size that can be sold as a rough stone and still be priced at under $10,000. Anything larger than that should be considered a jewelry piece rather than a gemstone. The best way to determine the quality of a diamond is by its color. Color ranges from colorless to extremely dark (almost black). Diamonds are classified by their color as well as their clarity. There are also diamonds with other special colors such as pink, yellow, and white. These do not come from natural sources; instead, they are produced through laboratory techniques (see below). Colorless diamonds are the most valuable because they are the hardest to colorate in the diamond mine. Pink diamonds can be treated by heating them to very high temperatures, which removes much of the pink color and makes them more white. Yellow diamonds can be made more white by irradiating them with ultraviolet light. This process does not change the quality of the diamond but it can make it more durable if it is used on jewelry that is frequently worn or exposed to sunlight.