How We Choose the Best Gemstones
Updated: May 11, 2022
Diamond & Moissanite
We only choose the best gems for our jewellery. Classic white diamonds and moissanites are graded by the same scales. 4Cs stand for colour, clarity, cut, and carat weight. The most precious stones are colorless (DEF) or near-colorless (GHIJ) and we give our preference for these. Fancy coloured gems need to have vivid deep colour. Pure coloured gems without any secondary hue are traditionally more valuable, however in coloured stones aesthetic beauty is the most important factor.
Another important factor to consider is clarity of a stone. For moissanites it is never an issue, because these are lab-grown and therefore, do not have inclusions that occur in natural stones. As for diamonds, again, we choose the perfect stones with such microscopic inlusions that are not noticeable with nacked eye, they correspond to clarity IF, VVS and VS.
4Cs are also used to determine the value of an emerald. The most important of these four is color. The best color is vivid green or blueish green with even saturation and no color zoning. A gemologist judges a diamond's clarity grade by using a 10x loupe while the clarity of an emerald is often assessed with the naked eye. Natural emeralds are typically included while the rare clearest specimens are very expensive. In general moderate inclusions do not spoil the overall look of an emerald. Emerald inclusions are often described as looking mossy or garden-like. They’re sometimes called “jardin,” which is French for garden. However, when the inclusions have a negative effect on transparency and clarity, they also dramatically reduce value.
Talking about emeralds, it's quite important to mention treatments that may be applied to these stones to enhance their characteristics, especially colour and clarity. There are many treatments and enhancements regularly applied to emeralds. Because most emeralds have tiny fissures that reach the surface of the gem, it is possible to fill internal inclusions by forcing oil through the surface-reaching fissures. Thus, oil hides flaws and improves colours, however, these concealed flaws could make the stone more fragile than it appears. It may even be unsuitable for jewellery use. Another problem with oiling is that it eventually wears off and after many years of wear, you may wish to have your emerald re-oiled. We do not use oiled emeralds in our jewellery.
Emeralds are occasionally colour-enhanced by introducing dye into surface reaching fissures to deepen the green color of less valuable lighter emeralds. This treatment is easily detected by observing the emerald under magnification. None of the emeralds we offer have been colour-enhanced by introducing dye. Unlike rubies and sapphires, emeralds are never exposed to heat treatment to enhance colour or clarity.
Sapphire & Ruby
In coloured stones colour is one of the most important factors determining its price and attractiveness. Besides blue sapphire and red ruby, the corundum family also includes so-called “fancy sapphires.” They come in violet, green, yellow, orange, pink, purple, and intermediate hues. There are also “parti-coloured” sapphires that show combinations of different colors. Some stones exhibit the phenomenon known as colour change, most often going from blue in daylight or fluorescent lighting to purple under incandescent light. Sapphires can even be gray, black, or brown.
The most valuable type of sapphire is the cornflower blue colour, known as Kashmir Sapphire or Cornflower Blue Sapphire or dark blue also called Royal Blue especially popular in the Western world. Another valuable sapphire form is the very scarce, orange-pink Padparadschah. An exotic type of sapphire, also called the Color Changing Sapphire, displays different colours depending on lighting. In natural light, this colour changing sapphire turns blue, but in artificial light, display a violet colour. The yellow and pink sapphire have become very popular, and are often seen in jewellery too.
Blue sapphires usually have some inclusions, but generally have better clarity than rubies. Several types of inclusions can be found in various sapphires. An example of this is the long thin mineral inclusions called needles. They typically also will have feathers or white, cloudy lines inside that can make the sapphire look opaque. It is very rare to find blue sapphires with extremely high clarity, making them very valuable. Price goes up with rarity.
The most popular treatment for corundum is heating. Very hight temperatures are used to improve dull-looking stones, the changes result in more vivid colour and better clarity. Interestingly, heating may occur naturally as well. Because changes brought by heating are permanent, we accept sapphires and rubies that went through this procedure.
Aquamarine is also a member of the beryl family, like emerald but it has rather very different characteristics. It is valued for its delicate colour and excellent clarity and transparency. It is also one of the few fine gemstones that can be found in large sizes at affordable prices, while very big natural aquamarines can still be very expensive.
Aquamarines can range in colour from blue to green, but the pure blues are the more valuable nowadays even though green hues were more popular in the Victorian era. Green aquamarines are often heated to reduce the yellow, so a clean unheated blue aquamarine with good colour saturation is a rare and valuable gem. Darker-toned aquamarines usually command the highest prices in the market.
Because of aquamarine's transparency and light colour, inclusions tend to be highly visible and can impair the beauty of the gem. Most high quality aquamarines are graded "loupe clean" or "eye clean," meaning that any inclusions are not visible with the naked eye.
Keep an eye out for imitation stones. Blue topaz is considerably less valuable than aquamarine, but the two stones can look similar. Avoid gemstones labeled as "Brazilian Aquamarine" or "Nerchinsk Aquamarine," since both of these actually refer to blue topaz. And also "Siam Aquamarine," which is actually blue zircon.