June 24, 2021
On the photo: a unique sample of the unheated yellow sapphire with the top Golden yellow color
In this article we will touch on a topic that is relevant for connoisseurs. It’s about how to choose sapphire, but not classical blue, which everyone is used to, but rare golden color. Natural yellow sapphire is an exquisite gem and a real treasure that has absorbed the warmth of the sun. It is also loved by fans of esotericism and astrology, as if this stone is filled with energy, it promises wealth and prosperity. It is also one of our company’s favorite gemstone. Let’s see what characteristics determine the value and how to decide which stone is will be right for you.
The range of colors of this variety of corundum contains warm shades of yellow from very light to bright golden orange-yellow. Sapphire is practically never has lemon color, in some samples there is a slight additional greenish tint. From the point of view of psychology, the yellow color represents optimism, self-confidence, the desire to look to the future with hope. The value of sapphire directly depends on the hue, brightness and color saturation. More than 90% of yellow corundums are naturally light in color, which can be described as a “straw” hue. The top, most valuable shade, according to the gemological community, is Golden Yellow.
Corundums including precious yellow sapphires are popular objects for treatment. An acceptable method for changing color is heat treatment. Light-colored crystals are heated to increase the intensity of yellow, so you can get saturated, bright and orange colors. The color obtained in this way is stable, do not be afraid that it will fade. The color changes in the entire volume, so that the heated sapphire can, if necessary, overheat or re-polish. Despite the fact that the most of yellow and orange sapphires on the market are treated, there is a small percentage of stones that have a beautiful golden color by nature. They are called unheated or untreated, abroad they are marked with the letter N – «natural». Such natural sapphires are priced more expensive than warm ones, but with respect to the cost of the blue variety, they can be considered significantly more affordable. We prefer to select unheated specimens for our collection, since the lack of treatment enhances the investment potential of sapphires and makes them more valuable.
In appearance, it is impossible to determine whether the stone was subjected to temperature, this is possible only in laboratory conditions. Another common method is heat treatment with beryllium diffusion. The peculiarity of this treatment method is that beryllium particles penetrate the stone structure and cause the appearance of a yellow color. We avoid specimens treated by diffusion. Diffusion sapphires are very cheap compared to natural sapphires. They are more characteristic of the Thailand market. Often calibrated light corundums are stained in this way.
Natural yellow sapphire crystals, suitable for cutting, rarely reach large sizes. The most common samples are up to 2 carats. Faceted yellow sapphires from 3 to 5 carats are much less common, they are suitable for everyday jewelry, rings and pendants. Ten carat size samples of beautiful bright color and high clarity are already considered a successful find. Large bright specimens with high clarity – over 15 carats – are extremely rare. Such unheated yellow sapphires are bought not only for jewelry, they are considered for collections and investment purposes, as a long-term investment.
On the photo: comparison of gemstones weighing 6.56 carats (left) and 4.13 carats (right)
Yellow sapphires, like other corundums, according to the GIA clarity classification are type II and usually with inclusions. However, high clarity specimens, VVS-VS, are found. These are visually pure stones, inclusions in which are possibly present, but are so small that they have no effect on optical properties, strength and beauty. Subtle internal inhomogeneities may be present, and if they are located in the peripheral zone, they are often not visible at all. Stones with such clarity are valued above all. And, on the contrary, yellow sapphires with a large number of inclusions and obvious noticeable cracks are valued cheaper, but at the same time their beauty is much worse. Most often in yellow sapphires there are gas-liquid inclusions in the form of fingerprints.
The insidiousness of yellow sapphires lies in the fact that inclusions are often found in unheated samples as in the photo, which may be mistaken for rutile needles partially dissolved after heat treatment, unlike sapphires of other colors. Yellow sapphires are also characterized by color zoning.
For such rare stones in good gem quality the principle of maximum conservation of the weight is applied. The most common shapes are oval and cushion. Shapes such as octagon (radiant or step cut) are less common. It is almost impossible to find yellow sapphire in the form of a pear, marquise or heart. These are only single stones in the market.
On the photo: yellow sapphire shapes of cut. From left to right: round, emerald, radiant, heart, square cushion, radiant.
As for calibrated small stones, without special research it does not seem to determine the presence of treatment and method. For example, often small yellow sapphires sprinkled with are treated with beryllium diffusion.
Yellow sapphires are often found in alluvial deposits, in which other colors of crystals and minerals are also found. The following countries are suppliers of gem crystals:
However, Sri Lanka is considered the classic place to mine these gems. There are crystals suitable for cutting individual specimens with good natural color and clarity. Yellow sapphires from other deposits, for example, Burmese samples, have much lighter colors. After cutting, the weight of stones from these deposits rarely exceed 5 carats.
A precious gem such as yellow sapphire has imitations and fakes. Glass (paste) is the most budgetary imitation. In such modern imitations like sital it turns out to achieve optical properties that are close to the characteristics of natural corundums. They can be distinguished by gas bubbles, sometimes large enough when viewed through a polariscope. The samples show a picture of anomalous anisotropy, beams, and stress zones. The refractive index of natural corundum will be quite high for glass and sital. In corundum the hardness is 9 on the Mohs scale, in glasses – 5-6. The most accurate imitation can be considered a synthetic analogue of yellow sapphire – man made yellow corundum. Its chemical composition, properties and appearance in faceted form are as close as possible to natural stone.
Currently, technology allows to obtain a wide range of shades corresponding to the natural color, depending on the addition and concentration of coloring impurities. Often, cubic zirconia is used as an imitation of yellow sapphire. Its high characteristics (dispersion, hardness, refractive index) provide a spectacular appearance of faceted stones. However, brightness of cubic zirconia even with the naked eye, allowing you to understand what kind of material is in front of you. Still, natural yellow sapphire has a more modest noble luster.
Also, natural golden corundum in some cases shows similarities with other stones. The most common comparison with fancy-colored diamonds. Citrine, gold imperial topaz, zircon, and occasionally chrysoberyl are also considered similar.
The price of the stone will undoubtedly be high because its supply on the world market is limited, and top-quality specimens are incredibly rare. But there is consolation that the yellow variety of corundum is much lower in cost of blue and cyan. Demand for yellow sapphires is growing and there are fewer and fewer offers, so price growth is possible in the future. Undoubtedly, unheated specimens of top colors possess the investment potential, since they are the most rare and in demand among collectors and investors.
In this article, in order to navigate freely in gradations of quality, we give price reviews. The most common among unheated specimens is a light yellow tint, so we will consider this gradation in more detail. So, as a reference point, we take the following characteristics. Light yellow, not heated, eye clean or with barely noticeable inclusions, medium asian cut quality, origin – Sri Lanka.
On the photo: a 10-carat untreated light yellow sapphire, Ceylon
A two-carat stone will cost approximately 300-400 US dollars / ct. The cost per carat of a five-carat sample will be 750-1000 USD. Ten carat size – 900-1300 dollars per carat. Offers of 15 carat stones and above start at 1500 per carat, since such specimens are single in the market and their price is set individually.
The presence of large cracks and contrast inclusions in the central part of the stone reduces the price. As for very light sapphires, they are usually priced at half the price. Unheated yellow sapphires of top colors (from intense yellow to golden color) will cost about 2-3 times more expensive depending on the color saturation and weight. A stone with high-quality cutting and polishing of top level is rated significantly higher than average quality which usually can see in asian market. And if there are significant symmetry violations, for example, the excessive depth of the pavilion, a large window, the displacement of the site, the world’s less valuable.
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