The term sapphire alone describes the blue variety of gem corundum. Other colors have a color prefix, i.e., yellow sapphire, green sapphire, etc. The term ruby is reserved for corundums of a red color. In Asia, pink corundums are also considered rubies. Outside of Asia, such gems are generally termed pink sapphires

Sapphires are identical in every attribute to ruby, except for one key component - their color. Found in a kaleidoscopic assortment of colors that range the entire spectrum, sapphires are broadly split into two named groups:

Lighting

Sapphires generally look best viewed with fluorescent light or daylight (particularly around just after sunrise and before sunset). Incandescent lights, whose output is tilted towards the red end of the spectrum, do not do most blue sapphires justice.

Clarity

In terms of clarity, sapphires tend to be cleaner than ruby. Buyers should look for stones which are eye-clean, i.e., with no inclusions visible to the unaided eye. In the case of some sapphires, extremely fine silk throughout the stone can actually enhance the value. This is the case with the famous sapphires from Kashmir, which display a velvety blue color with little extinction across the face.
While a certain amount of silk is necessary to create the star effect in star sapphire, too much silk desaturates the color, making it appear grayish. This is not desirable.

Shape & Cut

Faceted sapphires (those with flat polished faces) are found in a variety of shapes and styles. While ovals and cushion cuts are most commonly seen, other shapes such as emerald cuts and hearts are not uncommon.

Slight premiums are levied upon round cut sapphires due to the higher carat weight loss of expensive rough crystal during cutting. Conversely, discounts are often applied to the value of both pear and marquise cuts.

A perfectly cut sapphire should exhibit good symmetry and polish conditions, facets should be aligned straight in relation to the gem’s girdle and also to each other, polish condition should be good with no visible surface pits or polishing lines.

It could be argued that cabochons are the most common form of cut seen in sapphire. Often used to develop and display asterism in star sapphires, cabochon cuts are most regularly applied to those sapphires whose clarity is not ideal for faceting. Well-cut proportioned cabochons with good symmetry that are semi-transparent with smooth un-cracked domes are the ideal.

Stone Sizes

Blue sapphires occur in far larger sizes than ruby, with Sri Lanka being the home of most of the faceted sapphires of quality in the 100-ct. plus range. Any untreated ruby of quality above two carats is a rare stone. Fine untreated rubies above five carats can be considered world-class pieces.

Phenomena

Sapphire may display asterism, the star effect. Fine star sapphires display sharp six-rayed stars well-centered in the middle of the cabochon. All legs of the star should be intact and smooth. Just having a good star does not make a stone valuable. The best pieces have sharp stars against an intense blue body color. Lesser stones may have sharp stars, but the body color is too light or grayish. On occasion, 12-rayed star sapphires are found.

Sources

The original locality for sapphire was most likely Sri Lanka (Ceylon). Fine stones have also been found in Kashmir (India), Mogok (Burma), Madagascar, Thailand and Cambodia. Dark, inky blue sapphires come from Australia, China, Vietnam, Laos, Nigeria and a host of other localities. Fine blues of small size have been mined at Yogo Gulch, Montana (USA), while lesser stones have been produced elsewhere in Montana. Other sapphire localities include Kenya, Tanzania, Malawi and Rwanda.

Carat Weight

Large sapphires of high quality are rare and highly prized. Although not as valuable as large rubies, any high quality piece above fifteen Carats is considered extremely rare. As the Carat weight of a sapphire increases, so does its price per Carat. Large sapphires are many times rarer than smaller sapphires, meaning Carat prices increase disproportionately - a five Carat sapphire is worth many times more than five one Carat sapphires of a comparable quality.

Prices for sapphires increase in stair-like steps when in excess of certain significant Carat weights. For example, a 2.02 Carat sapphire commands a higher per Carat price than a 1.98 Carat sapphire, despite a negligible difference in actual size. Sapphire pricing, like that of nearly all other gems, suffers from a “non-linear-scale of increments”.

The Use Of Heat

Most sapphires seen on the market today have been subjected to high temperatures in an age-old practice that is said to have originated in Sri Lanka some 2,000 years ago.

Sapphires are heated at high temperatures to improve their clarity and to intensify their colors. Without this practice, we would see fewer sapphires on the market today, at far higher carat prices due to restricted and narrowed supplies. Heating sapphires makes otherwise expensive gems, more accessible and more affordable.

The proportion of unheated sapphires on the market is small and is widely thought to be less than 1%. Although no more beautiful, their rarity makes them highly collectable and prices are set at a premium, sometimes fetching triple the price paid for an equivalent heated sapphire. When purchasing unheated sapphires, please be aware that unheated material is rare, as a result, always purchase from a reliable supplier who guarantees their gemstones or have the seller’s claim verified by a qualified expert.