Authenticity

Like ruby, the origin of a sapphire is crucial to its value; as Burma is to ruby, so Kashmir is to sapphire. Few stones are still mined in Kashmir, and the gem-quality Kashmir sapphire displays a perfect velvety mid-blue, often showing a characteristic sea green dichroism when light passes through it.

The epithet ‘sleepy’ is frequently attributed to these stones, attributable to their subtle milky hue resulting from minuscule liquid-filled cavities or crystals, which remain difficult to detect even with microscopic examination. A more prominent feature is ‘zoning’, in which the coloration manifests in parallel bands. Moreover, Kashmir sapphires exhibit the remarkable quality of retaining their color even in artificial light, a notable exception among gemstones.

From a buyer’s perspective, the distinctive cornflower blue of a fine Kashmir sapphire is unforgettable and stands out from common stones. Unfortunately, many spend years in the jewelry trade without encountering one, but such comparisons are essential for assessing the color of other fine sapphires.

Burmese sapphires are typically high-quality with a saturated ultramarine blue color.. Conversely, Sri Lankan sapphires are usually paler and can be nearly colorless, with top stones resembling Kashmir blues. Both types exhibit inclusions resembling fine white needles and liquid-filled feathers, which reflect light when the stone is rotated. In Burmese stones, these ‘silk’ inclusions form short clusters of needles that are angled at 60 or 120 degrees when examined under a lens.

In Sri Lankan stones, the ‘silk’ is usually longer and often runs in one or two directions. The presence of ‘silk’ indicates genuine stones, but noticeable ‘silk’ visible to the naked eye can lower value unless it creates a ‘star’ effect.

Another notable characteristic of Sri Lankan sapphires is the presence of zircon inclusions; zircon is frequently encountered alongside sapphires in gemstone gravels within the region. As a mildly radioactive substance, zircon can disrupt the crystal lattice structure of nearby host materials, resulting in the formation of a distinctive ‘halo’.

Thai sapphires are typically deep in color, resembling blue spinels, while the deepest colored sapphires, considered least valuable, are from Australia and can appear black under certain lighting. Notable sapphires are also mined in Cambodia, particularly in Pailin, and in the late 19th century, Montana produced ‘new mine’ sapphires known for their pale electric blue hue, often found in pre-World War I jewelry.

evaluation

Sapphire is widely regarded as one of the most aesthetically appealing gemstones, yet it does not hold the title of the most valuable. In comparison, exceptional Burmese rubies can command prices of up to $150,000 per carat, while remarkable sapphires may attain approximately $80,000 per carat. Ultimately, prices are dictated by the demand for these rare specimens.

Unlike ruby, large sapphires over 50 carats are not very rare, but a Kashmir stone of this size is virtually unknown; those over 10 carats from Kashmir command high prices.

Burmese sapphires typically command prices that can reach as high as $40,000 per carat, while Sri Lankan sapphires are generally valued at less than $15,000 per carat.

Heat treating sapphires is a common practice that removes ‘silk’ and lightens the color of deeply saturated stones. This process is widely used for sapphires mined in Australia, making it challenging to determine the true origin of sapphires from Bangkok. While commercially acceptable, heat treatment can significantly reduce a gem’s value if identified.

Sapphires are rarely unaffected by artificial light, particularly electric bulbs that emphasize red wavelengths, leading to noticeable color changes, especially in some Sri Lankan sapphires that can turn purple at night due to chromium. This undesirable color change can decrease the stone’s value. It’s advisable to use a pocket torch when purchasing a sapphire, as even high-quality Burmese stones might appear different under such light. Ultimately, consider that jewelry is primarily worn at night.

Alternative Blue Gemstones Mistaken for Sapphires

Recently, a newly identified material known as ‘tanzanite’ has emerged in the marketplace. This blue variety of the mineral zoisite exhibits certain characteristics that can closely mimic those of sapphires. Nevertheless, even the highest quality specimens possess a blue hue that deviates slightly from the true color of sapphires, typically exhibiting a distinctive reddish tint.

A simple examination using a refractometer will highlight this distinction, as tanzanite has a refractive index in the vicinity of 1.70, while sapphires range from 1.76 to 1.77.

Blue spinel may exhibit similarities to sapphire; however, due to its typically dark and inky coloration, only low-quality sapphires might be confused with it. A rapid refractive index test can provide clarity, as spinel has a refractive index of 1.72 and is singly refractive.

Other Practices

Sapphire can appear flawless, which raises the possibility of it being synthetic in the absence of inclusions; detecting synthetic sapphires is similar to detecting synthetic rubies, with curved lines and gas bubbles being more evident. However, in some cases ‘Silk’ can also be produced in synthetic star sapphires.

Recent innovations may complicate detection in the jewellery market, particularly with small synthetic sapphires which are harder to identify, especially in pieces made between the wars. An ultraviolet light source can be beneficial for amateurs, as synthetic sapphires typically emit a palish green glow under short wave ultraviolet light due to excess titanium. Natural sapphires, however, remain inert under the same conditions, making this quick test valuable, especially since it’s rare for both types to be used together in larger numbers.

Synthetic blue spinel is infrequently engineered to mimic sapphire, with a higher prevalence of resembling aquamarine, and it prominently displays a bright red hue when viewed through a Chelsea filter. Additionally, it possesses a unique absorption spectrum attributable to the incorporation of cobalt as a coloring agent, alongside its association with pastes and composite stones.