Revealing Gem Cuts for Soft Gemstones

Gemstones are the “Humpty-Dumptys” of the jewelry industry. Once they’re cut, it’s impossible to put them back together again. Moreover, not all stones are created equal. Sidewalk chalk is great for hopscotch, but try to fashion it into a faceted ring and you’ll end up with a pile of powder!

Mohs Scale	Mineral	Example	Absolute Hardness
1	Talc	Talcum powder	1
2	Gupsum	Plaster of Paris, gypsum board	3
3	Calcite	Found in limestone and seashells	9
4	Fluorite		21
5	Apatite	A source of phosphorous	48
6	Orthoclase	A type of feldspar	72
7	Quartz	Amethyst and Citrine	100
8	Topaz	Also emerald and aquamarine	200
9	Corundum	Sapphire and ruby	400
10	Diamond	A girl’s best friend!	1600

In 1812, a German named Frederich Mohs devised a scale to gauge the relative hardness of minerals. He put talc at the low end (#1) and diamonds rated as the hardest mineral at #10. Although the Mohs scale was created for geological use and is relative rather than precise in measurement, it remains an excellent aid in choosing appropriate settings and gem cuts for precious stones. Yet on the table below, you see that diamond is actually 1600 times as hard as talc!

Besides the hardness of the gemstone, an equally compelling reason to use a variety of cutting and polishing techniques is to maximize the characteristics of a gem in a way that literally brings its true beauty to light. When cut into facets, hard transparent stones like diamonds and rubies refract light and allow it to expose their best qualities. However, many translucent gemstones like opals and opaque stones like turquoise have qualities that facet gem cuts simply leave on the cutting room floor.

The first step in creating a jewel from a gemstone is removing any loose or fractured material from the piece. This process is called cobbing or cobb cutting. Some gems can be cut in several different ways depending on the result that the jeweler wants to create. For instance, the sapphire in facet gem cut offers a spectacular display of fire and ice, yet the facet cut would destroy the display of the gem with asterism, the six-pointed star you see in the “star sapphire”.

Cabochons: Smooth as silk but star sapphire bright!

The star sapphire is cut as a cabochon. The cab cut, or cabochon, is also the usual gem cut for opals and other iridescent gemstones. Stones “en cabochon” are shaped and polished, rather than cut. The result of a cab cut is a flat-bottomed (or slightly rounded bottom) stone with a convex or domed top. The traditional cabochon is an oval, but cabochons can be fashioned into triangles, rectangles, and other angular shapes as well.

One cabochon variation for transparent stones is the buff-top cut which mixes the facet gem cut with the cab cut and results in a stone with the typical domed top, where the pavilion (bottom) is faceted, giving an illusion of depth as the eye is drawn into the center of the stone.

The cut shows good briliance but has a more durable (less-easily abraded) crown than faceted stones will have.

Beading: “Every Pearl Has Its Oyster”

That’s what author Randall Jarrell is quoted as saying, but today many pearls come from fresh water mollusks instead of their salt-water cousins. However, strings of pearls have been popular since ancient times and were quite probably the forerunners of beading. Unlike the round pearl, most gemstones that are shaped into beads start out as a square block and are ground, tumbled, polished, and drilled before they are fashioned into a beaded string.

Inlays: Turquoise at its best

Inlaid gemstones are cut and shaped to fit inside another material and usually glued rather than put into a precious metal setting. After the stone is inlaid, the top is ground and polished to be flush with the surrounding material. Opaque stones, like turquoise and tiger eye are particularly lovely when inlaid since surrounding material can be chosen and stones can be cut to enhance their color variations.

Cameos: Oceans of beauty

Cameos have been prized throughout history for their intricate designs. Although most often displayed as a profile portrait, cameos can display a miniature artwork from still life to a complete scene. The cameo is traditionally carved from seashells and attached to a precious stone in a bezeled setting. A variant of the cameo is the intaglio, which is a design that is carved directly into the gemstone.