Diamonds with Gray as the primary dominant color are unique. These diamonds are comparatively reasonably priced and have a perceived color resembling the color of the metal nickel, aluminum, or pewter.
Gray is a neutral color containing little or no saturation. The addition of small quantities of blue or green will produce a cool gray color, while the addition of brown or yellow will produce a warm gray color.
Common names for gray color diamonds include charcoal gray, steel, pigeon, slate, silver etc.
The gray diamond rough is mined in Australia, South Africa, India, Russia and Brazil.
Gray diamonds are colored by hydrogen, and more rarely boron (unknown how, since boron nearly always forms blue). The defect causes the stone to absorb all wavelengths of light equally. Gray color can tint nearly every other shade. Gray colors often appear very different when viewed under average natural daylight versus an artificial light source. Natural gray diamonds occur within a specific region of color tone. Their lightness extends from very light (smoke) gray, through dark (graphite) gray colors.
Enhanced gray colors are rarely made due to easy availability of natural gray diamonds.