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Sapphire: cut, treatment and varieties

Sapphire: cut, treatment and varieties

June 24, 2021

On the video: process of faceting in Thailand

Appearance of sapphire depends on attractiveness of form. The cut and shape of a gemstone is an important factor as well. The symmetry, proportions and the absence of damage are signifiant things. In order to save maximum of the weight cutters may make a big pavilion which is not so good. Or the opposite thing may happen: when the stone has a small pavilion then you may see a «window» when looking from the table. Both factors influence the beauty of the particular stone and therefore its price.

the heart-shaped sapphire

In the photo: the heart-shaped sapphire 3.03 ct from Sri-Lanka. Pay attention on the large «window» in the centre, light does’t return in an eye of an observer.

“Practical advice. Look at stone and check if the shape is nice and if the stone has right proportions. Notice if the chosen sapphire has a good symmetry and, if it has a «window», does it influence the beauty in general. Check the proportions of pavilion. See how well is the stone polished and if it has any scratches. Don’t forget that some of the defects may be removed by recutting that doesn’t cost much.“

Treatment

A lot of sapphires are being enhanced in order to get a better color and sometimes clarity. The most popular kind of enhancement is heating. Sapphires are being heated in special ovens at 800-1900 degrees Celsius. As a result one may get a brighter piece and sometimes lighter color or to remove some shades at all. The improvement of clarity happens when thin «needles»of rutile are being melted. About 90% of all blue sapphires on the market are being heated.

The price of unheated sapphire can be 1,5-2 times more then the heated one of the same quality. The reason for this is that fine quality sapphires are unique to be found in nature. Some pieces are being heated together with titanium oxide which is called titanium diffusion. In this case only a surface of sapphire is being colored in a bright blue color. If recutting this piece, the bright layer may be removed and a real color of the stone may appear. Those were two main methods of enhancement for blue sapphires. The factor of enhancement influence the price a lot so it is highly recommended that the stone has a gemstone report from an authoritative gemological laboratory that would prove its natural origin.

In the video: treated by beryllium diffusion large sapphire. Only near-surface layer colored in bright blue color.

Origin

The price of sapphire may also depend on its origin. The most expensive blue sapphires traditionally come from the Northern state of India – Kashmir. However now this mine is closed and therefore Kashmir sapphires are very hard to be found and are mostly being sold on the auctions. Kashmir sapphires usually have rich blue color that reminds of velvet due to tiny inclusions of rutile. It’s interesting to know that nowadays the term «Kashmir» doesn’t only indicate the origin but also may refer to the color. On the second place we have sapphires from Myanmar (Burma) and also from Sri Lanka. These three countries are the most popular origins for blue sapphires that you find in a gemstone report. Recently nice blue sapphires started coming from Madagascar. Sapphires from Thailand, Cambodia, Laos and Australia are mostly dark and quite small. You may also hear of mines located in Tanzania and Nigeria but it’s unlikely to find a good piece there.

In the image: a map of sapphire deposits

Sapphire origin

Certificate for sapphire

Sapphires may not only come from nature but also can be made by human. Synthetic sapphires may have a good color and great clarity but their price is very low because they can’t be rare. To prove that a sapphire is natural and also diagnose enhancement, origin and the type of color one should order a certificate from an authoritative gemological laboratory like GIA, Gubelin Gem Lab,SSEF and AGL. GRS is also a popular laboratory, especially in Asia.

In the left photo: a certificate from GRS laboratory.

Certificate for sapphire

“Practical advice. Ask the seller if the stone a gemstone report or a certificate. What origin does it have? Has it been enhanced? If yes, then by which method? All these questions will be answered in a gemstone report. And, of course, the report will make sure that the stone is natural.

Varieties of sapphire

Blue sapphires are also presented by their gemological varieties. For example, some of them posses an optical effect (beside the color-change effect mentioned earlier). Star sapphires have an asterism effect: you may observe a 6-ray star on the surface of cabochon sapphire. Another optical effect that you may encounter is a cat’s eye effect: a white moving stripe on the surface of cabochon sapphire. Both effects appears due to the concentrated needles of rutile. If such sapphires are heated, then these needles will be melted. There is also an unusual variety of sapphires called «trapiche» that is highly appreciated by collectors and is very rare to be found in jewelry. This type of sapphire has 6 sectors starting from the centre and divided by white rays.

On the video: star sapphire from Sri Lanka

– At the first part of the article we tell about color, clarity and weight of sapphire.

– At the third part of the article we show real prices per carat on a blue sapphire.

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