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Precision Cuts: Are they For You?

Posted by Yvonne Raley on

If you are addicted to gems, you will soon find yourself getting attracted to precision cut gems – gems that have unusual shapes and more intriguing faceting patterns.  But setting gems like these is a whole other story. The cutter’s objective – bringing out the best of the gem – often conflicts with jewelry design and ease of setting.  So before you sink all your spare change (and then some) into a precision gem, keep these pointers in mind.

If you don't want to spend a ton of money having a custom setting made, you need to stick to shapes for which commercial settings are available. Prong settings are come in round, oval, square, marquis, pear, pear and emerald shape, as well as some baguettes. For other shapes you have to adapt an existing setting. Octagons and hexagons can go into round settings, cushions fit in into squares. Some rectangular cuts can fit into emerald settings. Prong settings are forgiving and can tolerate a fit that is not exact. Figure a tolerance level of .5mm, but buy the setting .5mm larger if you’re not sure. Undersized prong settings are often too shallow and the prongs will not fold over the stone.

Bezels have to fit precisely, with at best .01 mm to spare. There are no commercial bezels for rectangles or baguettes. Otherwise they are the same as prong. Cushions do not fit into any commercial bezels.

Also keep in mind that colored stones tend to be deeper in cut than diamonds because they are cut for color optimization. The deepest and bulkiest cut is step cut which is common for sapphires. They have a heavy belly, as we say. Portuguese cuts are also s bit bulkier. So you should ask about the depth of a stone if that is not listed. Most settings are made for brilliant cut stones. The depth of a brilliant cut is 65 per cent of the width and that’s the proportions for which most settings are made. For prong settings, this means you may need longer prongs. For bezels you need depth or else the stone sticks out the back once it is set.  Remember that for a ring, the back of the setting has to be rounded out, so you have to subtract a couple of mm.

Ouch - this will hurt

Another point to bear in mind is that girdle thickness is an issue for straight bezels with a pre cut bearing wall. The gem might "spill out" and the bezel walls will not fold. An alternative is to have the jeweler buy tube (which comes in round, square and oval), and saw off a piece in the right length to fit the overall depth of the stone, then drill the bearing wall.  But that means that the jeweler has to buy tube and cut it to size, which can cost more. 

Bezeling doesn't work well with a round stone has corners cut into the girdle. The only bezeling option is to cut all the corners into the bezel itself and then hope the pressure from setting doesn't bust the gem. But there are no pre-cut bezels for stones with corners except for princess and emerald (there certainly aren't any for octagons). Also, that kind of setting is beyond the expertise of most setters – it hardly ever comes up so nobody gets a chance to practice.  And you don’t want your gem to be the guinea pig.

Finally, bezel setting implies that more pressure is applied to the stone than in prong setting. Especially when the bezels are thick, because thick bezels are literally hammered around the stone with a miniscule “jack hammer.”   Many gems cannot handle that, especially when the bezel is gold, which is much harder than silver and requires even more pressure. Also, it is preferred that the gem doesn’t have corners.  Hammer setting emerald cuts, for instance, is extremely difficult. Princess cuts are nearly impossible. One wrong move and the corner chips or causes a crack that goes through the entire gem.  Some gems, i.e. tanzanite, can break straight through.

This bezel is for hammer setting, the side view is the same as the one above
In summary: think “prong setting”, avoid gems with corners, avoid setting soft stones in hard metals, and run with cuts for which there are existing settings. 

Amazing but at best a pear prong setting works (the wire will show because it's per shaped, not trillion)

This is gorgeous but it will only fit into an emerald cut or oval prong setting

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