How to Buy a Sapphire - Part 2
Burmese and Kashmir Sapphires are the most sought after varieties, known for their superior clarity, hue and saturation. Kashmir sapphires are mostly found in the resale market, since few sapphires are now mined from that war-torn region in Asia. Burmese sapphires of comparable quality also command high prices. Thailand has its superb quality Kanchanaburi alluvial-mined sapphires which are popular choices for high-end sapphire jewelry. They are relatively rare and of extraordinary beauty. Since 1996, exceptional quality sapphires have been recovered from alluvial deposits derived from basaltic rocks in Madagascar (an island-nation off the coast of South-East Africa). The crystal morphology, growth patterns, inclusions, absorption spectre, and trace-elements of these Madagascar sapphires are almost indistinguishable from other basaltic-magmatic sapphires – these sapphires are extremely well priced and are often found in high-end exclusive jewelry. Burma, Kashmir, Sri Lanka, Thailand, Madagascar, Australia, Cambodia, China, Colombia, Malawi, Nigeria, Tanzania, Vietnam, and the US are well-know sources of this striking gemstone.
Blue Sapphires tend to have more inclusions than most fancy-colour sapphires. Gemologists use the term “inclusion” to define characteristics found inside a stone. Inclusions are often used as an indication that the gemstone is of natural origin. A “blemish” is a characteristic that affects the stone’s surface.
- Crystals – solid inclusions of various shapes and sizes. Extremely Small crystals are referred to as pinpoints or grains.
- Silk – fine fibres of titanium dioxide (rutile) or other minerals that resemble the look of silk. Well-formed silk indicates that the sapphire underwent no heat-treatment and is of natural origin. Silk is a preferred inclusion in sapphires
- Needles – long, thin inclusions of either crystals, or tubes filled with gas or liquid (growth tubes)
- Cracks - feather-like inclusions also known as fractures or fissures
- Parting – breakage along a plane of weakness
- Twinning – two crystals grown out of one another or next to each other
- Halos – circular fractures surrounding a crystal
- Fingerprints - common in sapphires, these inclusions look like human fingerprint outlines
- Colour zoning – uneven colour distribution in the sapphire
- Cavities – holes extending into the sapphire from the surface
- Chips – broken off pieces along the girdle or on the cutlet of the sapphire
Sapphire Surface Blemishes
- Scratches – lines scraped on a gemstone
- Pits – tiny holes on the stone’s surface
- Nicks – broken parts of a stone’s girdle or facet
- Abrasions – rough scraping along the stone’s facet edges
The degree of visibility through a sapphire is known as its transparency. It is an often overlooked characteristic of sapphires. Transparency is designated as follows:
Transparent – objects look clear and distinct through the stone
- These sapphires usually have excellent brilliance despite any inclusions they may have
- Semitransparent – objects look slightly hazy or blurry through the stone
- Translucent – objects are difficult to see through the sapphire
- Light can pass through; somewhat diffused
- Semi-translucent or semi-opaque – a small fraction of light passes through the stone
- Opaque – almost no light passes through the stone
Different Cuts of Sapphire
The best sapphire cuts offer a depth/width ratio higher than comparable diamond cuts. Expect a depth percentage of 65% to 80% for good quality sapphires (the depth percentage is depth/width). Stones that are too deep will look smaller than expected but they will show off more colour than they would if they were cut to normal proportions. Deep-cut stones also preserve weight, increasing the cost of the stone without the expected increase in the size of the crown (top portion of the gem). Stones that are too shallow will look big for their weight and appear lighter in colour than deeper-cut stones.
Good quality sapphires also have good symmetry when viewed in profile – reflecting the light evenly.
The overall grade is determined by looking at Hue, Tone, Colour-Purity, Clarity, Transparency and Cut.
In the jewelry industry, it is assumed that sapphires have been heat treated unless otherwise specified. The Gemological Institute of America and other certification authorities accept heat treatment as a valid and acceptable modification; it is permanent and will not degrade over time. Other treatments that are available to the jewelry industry such as fracture filling (glass infilling of cavities), surface diffusion (surface colouring treatment), oiling dyeing or waxing are temporary in nature and may require future maintenance. We consider these treatments unacceptable for the quality of stones that we sell.
Sapphires are heated to improve its clarity and colour. At temperatures above 1700 degrees Celsius, the silk dissolves and improves the colour and clarity of the stone. This treatment can turn a colourless sapphire into a blue sapphire. At lower temperatures, silk can be improved and the colour lightened. Sapphires that have undergone no treatment of any kind are considered rare gemstones. These rare stones may sometimes cost in excess of $20,000 per carat.