The chromium concentration in artificial rubies can be adjusted (in the crystal growth process) to be ten to twenty times less than in the natural gemstones. Additionally, absorption at any of the above wavelengths stimulates fluorescent emission of 694-nanometer-wavelength red light, which adds to its red color and perceived luster. If one percent of the aluminium ions are replaced by chromium in ruby, the yellow-green absorption results in a red color for the gem. Note the two broad violet and yellow-green absorption bands and one narrow absorption band at the wavelength of 694 nm, which is the wavelength of the ruby laser.

Transmittance of ruby in optical and near-IR spectra. The world's most valuable ruby to be sold at auction is the Sunrise Ruby. Ruby is the traditional birthstone for July and is usually pinker than garnet, although some rhodolite garnets have a similar pinkish hue to most rubies. After color follows clarity: similar to diamonds, a clear stone will command a premium, but a ruby without any needle-like rutile inclusions may indicate that the stone has been treated. The brightest and most valuable shade of red, called blood-red or pigeon blood, commands a large premium over other rubies of similar quality. The quality of a ruby is determined by its color, cut, and clarity, which, along with carat weight, affect its value. Some gemstones that are popularly or historically called rubies, such as the Black Prince's Ruby in the British Imperial State Crown, are actually spinels.

The color of a ruby is due to the element chromium. The word ruby comes from ruber, Latin for red. Ruby is one of the traditional cardinal gems, alongside amethyst, sapphire, emerald, and diamond. Other varieties of gem-quality corundum are called sapphires. Ruby is one of the most popular traditional jewelry gems and is very durable. A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide).

Ruby sapphire