The quality of a ruby is determined by its color, cut, and clarity, which, along with carat weight, affect its value.

The brightest and most valuable shade of red, called blood-red or pigeon blood, commands a large premium over other rubies of similar quality.

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.

[7] 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.

"[8] After absorbing short-wavelength light, there is a short interval of time when the crystal lattice of ruby is in an excited state before fluorescence occurs.

Gemologists use these needle inclusions found in natural rubies to distinguish them from synthetics, simulants, or substitutes.

As a result of the difficulty and subjectiveness of such distinctions, trade organizations such as the International Colored Gemstone Association (ICGA) have adopted the broader definition for ruby which encompasses its lighter shades, including pink.

Historically, rubies have been mined in Thailand, in the Pailin and Samlout District of Cambodia, as well as in Afghanistan, Australia, Brazil, Colombia, India, Namibia, Japan, and Scotland.

After the Second World War, ruby deposits were found in Madagascar, Mozambique, Nepal, Pakistan, Tajikistan, Tanzania, and Vietnam.

The most recently found ruby deposit in Myanmar is in Namya (Namyazeik) located in the northern state of Kachin.

[16] In Pakistani Kashmir there are vast proven reserves of millions of rubies, worth up to half a billion dollars.

[23][24] Rubies, as with other gemstones, are graded using criteria known as the four Cs, namely color, cut, clarity and carat weight.

Transparent gemstones occur in the pure spectral hues of red, orange, yellow, green, blue, violet.

Most rubies at the lower end of the market are heat treated to improve color, remove purple tinge, blue patches, and silk.

[28] The process is done in four steps: If a color needs to be added, the glass powder can be "enhanced" with copper or other metal oxides as well as elements such as sodium, calcium, potassium etc.

[30] When jewelry containing rubies is heated (for repairs) it should not be coated with boracic acid or any other substance, as this can etch the surface; it does not have to be "protected" like a diamond.

[31] In 1837, Gaudin made the first synthetic rubies by fusing potash alum at a high temperature with a little chromium as a pigment.

In 1877, Edmond Frémy and industrial glass-maker Charles Feil made crystal corundum from which small stones could be cut.

In 1887, Fremy and Auguste Verneuil manufactured artificial ruby by fusing BaF2 and Al2O3 with a little chromium at red heat.

Synthetic rubies may have no imperfections visible to the naked eye but magnification may reveal curved striae and gas bubbles.

Dopants are added to some manufactured rubies so they can be identified as synthetic, but most need gemological testing to determine their origin.

[33] Maiman used a solid-state light-pumped synthetic ruby to produce red laser light at a wavelength of 694 nanometers (nm).

Rubies are also used in applications where high hardness is required such as at wear-exposed locations in mechanical clockworks, or as scanning probe tips in a coordinate measuring machine.