How to choose a gemstone?

First of all, regarding the stone trade, the decree of January 14, 2002 stipulates that the terms "precious stone," "semi-precious," or "fine" should no longer be used, but rather "gemstone." Although the term "precious stone" remains commonly used in everyday language, it should not be used in official commercial descriptions. On the internet, this term is still often present because Google does not take this French legislation into account, which sometimes forces sites to continue using it for SEO reasons.

Now that that's out of the way, here are some basic principles to know before buying a stone.

The beauty of a stone is personal and subjective. It is assessed from a reasonable distance in order to appreciate the rendering of the color, its capacity to reflect or even decompose light (fires).

On the other hand, financial value is assessed at high magnification (under a magnifying glass).

Although there is no specific price list for gems other than diamonds, we can draw inspiration from what has been done for the latter in order to evaluate the quality of a stone and be able to set a price accordingly.

To evaluate a stone, we can therefore use the 4C rule, initially established for diamonds, but which can be applied to any gemstone. In English they are:

Carat (weight) Clarity (purity) Color (color) Cut (size)

Evaluating a stone based on these four criteria doesn't give you a price, but it helps you understand its quality. And so you can see what compromises you're willing to make based on price. Because we often find ourselves having to compromise when choosing stones, with perfect ones often reaching prices that most people can't afford.

Weight (Carat):

The weight of gemstones is expressed in carats (Ct) and not in grams.

1 carat = 0.2g.

This term has nothing to do with the carat that we understand for gold, which in this case is a degree of purity.

Logically, the bigger and therefore heavier it is, the more expensive it is.

For the most sought-after stones in jewelry, the increase is not linear in relation to weight but rather exponential. For example, one 2 ct sapphire will cost more than two 1 ct sapphires of equivalent quality.

Purity (Clarity ):

The fewer inclusions (defects of all kinds) there are, the higher the price will be. We use 3 levels of description that can be nuanced:

• Visible inclusions when you see them just by eye.
• Clean to the eye if we do not see any inclusions when looking at the stone but we can see them with a X10 magnifying glass. In this case we specify whether they are more or less visible.
• Clean under the microscope when even with a x10 magnifying glass you can't see anything.

Color:

It's about naming it, but not only that. We'll evaluate the intensity of the color (saturation) and the brightness (clarity).

The Size (Cut):

The quality of the cut, that is to say the symmetry between the facets, their alignment and the polished finish, has a huge impact on the price because it affects the beauty of the stone. It is the only one of the 4Cs where there is human intervention.

A good cut can "erase" inclusions, making the stone more brilliant and therefore attractive.

Symmetry defects will reduce the stone's shine because they will have an impact on the angles of reflection that the light rays will make inside the stone.

If a stone is well cut, you should not see through it (this is not the majority of cases). All the light that enters the stone must come out after a play of reflection on the facets and must not pass through it. It is this play of reflection that gives the stone its brilliance. A very good quality stone without inclusions that is poorly cut will have its price devalued.

Often a good quality cut includes a greater loss of material at the time of cutting and since they are sold by weight some lapidaries (gem cutters) will favor weight to the detriment of quality. Or at least find a compromise between beauty and weight. And that's for a perfectly clean stone. If in addition it has to "hide" inclusions it becomes very complicated.... Especially since each type of stone will require specific angles to reflect the light.

Treatments:

In addition to the 4Cs, when evaluating the price, it is necessary to take into account whether the stone has been treated or not (such as heating). Many stones are treated and this can impact the price to a greater or lesser extent depending on the treatment. It always lowers it. I invite you to read the page on treatments if you want to know more.

It is important to know that stones that are completely clean under a magnifying glass are not the majority and, in the case of jewelry stones, can cost several thousand euros per carat depending on the size of the stone (and even much more for exceptional stones). They can also be synthetic...

The jewelry you "come across" every day with stones that seem completely clean to you usually has inclusions.

The larger the stone, the rarer it is to have no flaws. Therefore, inclusions are more tolerated on a large stone than on a small one. Of course, the size of the inclusion must not be proportional to the size of the stone.

A stone's inclusions can be seen as flaws in the person you love. It doesn't take too many, but their absence would make them unaffordable.

Finally, the best reason to buy a stone is to find it pretty.