Facts
- Mineral: Corundum
- Chemical composition: Al2O3
- Colour: Red
- Refractive index: 1.762 to 1.770
- Birefringence: 0.008 to 0.010
- Specific gravity: 4.00 (+/- 0.05)
- Mohs Hardness: 9
(Courtesy: GIA)
About Ruby
The word ruby comes from ruber, Latin for red. The colour of a ruby is due to the element chromium. Ruby is a pink to a blood-red coloured gemstone, a variety of the mineral corundum (aluminium oxide). Other varieties of gem-quality corundum are called sapphires. Ruby is one of the traditional cardinal gems, together with amethyst, sapphire, emerald, and diamond.
Ruby has historically been prized as the most precious and powerful gemstone in the world.
The two names in Sanskrit ‘Ratnaraj’ – King of precious stones and ‘Ratnanayaka’ leader of precious stones defines the stones noble indeed royal attractiveness.
Quality of Ruby
The quality of a ruby is determined by its colour, 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. After colour 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. 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.
A well cut gemstone reflects out l00% possible brilliance. One that is too shallow will have a dead spot in the center of the gem where light is lost out through the back. A deep stone will absorb too much light without reflecting back the brilliance; it will also be heavily bellied and may be difficult to set. You will pay for extra carats which don’t add to the gemstone’s beauty.
Factors Affecting Value of Ruby
Rubies, as with other gemstones, are graded using criteria known as the four Cs, namely colour, cut, clarity and carat weight. Rubies are also evaluated on the basis of their geographic origin.
- Colour: In the evaluation of coloured gemstones, colour is the most important factor. Colour divides into three components: hue, saturation and tone. Hue refers to colour as we normally use the term. Ruby is defined to be red. Ruby may exhibit a range of secondary hues, including orange, purple, violet, and pink.
- Cut: Rubies can be cut into many shapes and sizes. Most popularly, rubies are cut into a cushion, oval, pears, octagon shape. A well-cut gemstone reflects out l00% possible brilliance. One that is too shallow will have a dead spot in the center of the gem where light is lost out through the back. A deep stone will absorb too much light without reflecting the brilliance; it will also be heavily bellied and may be difficult to set. You will pay for extra carats which don’t add to the gemstone’s beauty.
- Clarity: People in the trade expect rubies to have at least some inclusions because inclusion-free rubies are rare. Ruby value can depend on how visible the inclusions are. Obvious inclusions, or inclusions that reduce transparency or brightness, lower a ruby’s value dramatically.
If large and prominent inclusions are located under the table facet, they greatly diminish the transparency, brilliance, and value of the stone. Inclusions can also limit a ruby’s durability. Significant surface-reaching fractures can pose durability threats.
Typical ruby clarity characteristics include thin mineral inclusions called needles. When the mineral is rutile and needles are present in intersecting groups, it is called silk. Needles might be short or long and slender, and they might appear to be woven tightly together. Ruby can also contain needles composed of other minerals, small crystals, and zones of colour variation, or inclusions that resemble fingerprints. Some inclusions can contribute positively to a gem’s appearance. The presence of rutile silk causes light to scatter across facets that might otherwise be too dark. This adds softness to the colour and spreads the colour more evenly across the ruby’s crown. Needles that intersect can also cause the star effect, called asterism, when the stone is cut with a curved upper surface, called a cabochon cut.
- Carat Weight: There are some gemstones such as the ruby, which are often found in large sizes. However, it is extremely difficult to come across a ruby with high clarity. Therefore, a much smaller ruby with few inclusions will cost a pretty penny. Additionally, a stone’s weight does not necessarily reflect its visual appearance. What this means is that a rather heavy stone may be very deep, and much of its weight will not be seen when set in a jewellery set. On the other hand, a much lighter stone could appear much larger simply because it is shallow but wide. Someone with a tight budget could benefit greatly from such a stone.
Care of Ruby
Use warm soapy water to clean ruby. In the case of fracture-filled, cavity-filled or dyed rubies, using a damp cloth for cleaning is always safe. Ultrasonic and steam cleaners are usually safe for untreated, heat-treated, and lattice diffusion treated stones.