The Egyptians and Indians had some appreciation of color in their cheap diamond jewelry. They added manufactured and natural stone and enameling to it, but by and large the best jewelry of most of the ancient world was wrought only in gold. However, by the time of Alexander the Great—about 350 B.C.—gem-stones were more frequently found in Greek jewelry. Rock crystal, agate, sardonyx, carnelian, and even emerald added color. Interest in polychrome jewelry diamond solitare earrings increased, stimulated by contact with Persia. The most riotous use of color in jewelry developed among Indian civilizations along the Indus River. An abundance of colored gemstones in this part of the world, the availability of pearls, and a knowledge of the techniques of colored enamel and glassy paste combined to make it possible.