One of the most popular style of gemstones in jewellery are faceted stones, especially diamonds. So let's take a look at this very specialized branch of lapidary. Faceting a stone means that the stone is cut with multiple flat polished surfaces at different angles. You can find beads and cabochons that are faceted, but for this post I'm going focus on the truly faceted stones, like the diamond. As I said in the last post, faceting is usually reserved for the higher quality transparent or translucent stones. The reason? The faceting process allows the light to be reflected through the stone and gives it that eye-catching sparkle.
There are two basic types of facet cuts, trap or step cuts and triangular or kite cuts. With these two cuts, there are so many shapes that can be done, I won’t even try to assign a number.
These are some of the more common shapes:
Faceted gems have their own particular nomenclature:
Gemstone sizes
Beads are usually sized in millimetres or inches by diameter or length and width. Cabochons are usually sized in the same fashion. Faceted stones are different, they’re usually measured in carats. A carat is actually a unit of weight; one carat = 200 milligrams (0.007055 oz). Because different stones have different densities, a 1 carat diamond may be a different size than a 1 carat sapphire. Find that confusing? Me too. Which is why, when buying a faceted gem, I look for the actual measurement of the stone.
Beads are usually sized in millimetres or inches by diameter or length and width. Cabochons are usually sized in the same fashion. Faceted stones are different, they’re usually measured in carats. A carat is actually a unit of weight; one carat = 200 milligrams (0.007055 oz). Because different stones have different densities, a 1 carat diamond may be a different size than a 1 carat sapphire. Find that confusing? Me too. Which is why, when buying a faceted gem, I look for the actual measurement of the stone.
Clarity of Transparent Gems
The clarity of a gem is directly related to its value. Inclusions in the gem (flaws), lower the value depending on how visible it may be. Many inclusions are not actually visible to the naked eye, but only to a skilled expert under magnification. Diamonds are graded for clarity in a slightly different manner to coloured gems such as rubies, sapphires, etc. There is no standard grading system for coloured gems, but these are the most common systems that I've seen.
The clarity of a gem is directly related to its value. Inclusions in the gem (flaws), lower the value depending on how visible it may be. Many inclusions are not actually visible to the naked eye, but only to a skilled expert under magnification. Diamonds are graded for clarity in a slightly different manner to coloured gems such as rubies, sapphires, etc. There is no standard grading system for coloured gems, but these are the most common systems that I've seen.
Diamonds
This system is meant for white diamonds. Coloured diamonds are not deemed to be as valuable as clear diamonds.
This system is meant for white diamonds. Coloured diamonds are not deemed to be as valuable as clear diamonds.
FL | Flawless | Flawless under 10x magnification by a skilled grader. Less than 1 in 5000 jewellery quality diamonds are given this rating. |
IF | Internally Flawless | Internally flawless under 10x magnification by a skilled grader. FL and IF appear identical except to an expert. Less than 3% of jewellery quality diamonds are rated IF. |
VVS1, VVS2 | Very Very Slightly Included | Inclusions are extremely difficult to see under 10x magnification. |
VS1, VS2 | Very Slightly Included | Inclusions are minor and only visible under 10x magnification. |
SI1, SI2 | Slightly Included | Inclusions are easily visible under 10x magnification but not usually noticeable to the naked eye. |
I1, I2, I3 | Included | Inclusions are visible to the naked eye and may affect the transparency and brilliance of the gem. |
Coloured Gems
Coloured gems often have inclusions, which is why they are graded differently than the diamonds. I have seen the diamond scale used for other gems, but even then, it's used a little differently. For many, the most important qualities of a coloured gemstone, is that it's eye clean (no flaws visible to the naked eye), and the colour is vivid and consistent.
Coloured gems often have inclusions, which is why they are graded differently than the diamonds. I have seen the diamond scale used for other gems, but even then, it's used a little differently. For many, the most important qualities of a coloured gemstone, is that it's eye clean (no flaws visible to the naked eye), and the colour is vivid and consistent.
Type 1 | Inclusions are detectable only under 10x magnification. |
Type 2 | Eye clean. |
Type 3 | Inclusions are visible to the naked eye. |
In my next post, I'll explain some of the treatments that gemstone are subjected to in order to enhance their appearance. Until then, happy creating!