Gemstones in the rough give hints of what they look like when cut and polished. Crystalline stones are faceted into jewels, whereas petrified wood, obsidian and other semi-precious rocks are shaped into cabochons. It all begins with saws and ends with polishing.
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Rocks and gems are cut with diamond-blade equipment. Diamond is the hardest mineral and, therefore, can scratch or chip other materials. Gem-cutting blades have varying grades of diamond chips in the edge. Diamond blades are available for band saws or slab saws, as well as for grinding and polishing saws.
The diamond-impregnated blades work by taking small chips off the gemstone. The thickness of the blade, the size of the diamond pieces and the feed rate and cutting rate of the material will factor into the type of blade you would need for your project.
When gemstone materials are to be ground, the diamond chips are impregnated into a wheel or belt, or into a polishing compound. The grit size of the diamond pieces determines how much material is taken on the different types of grinders and polishers.
A cabochon is a gemstone that you make into a rounded shape and then polish instead of faceting like a crystal stone. Cabochons, or cabs, can be small--as in a tiny pendant--or large, as in a cowboy's belt buckle. Most cabs are oval- or circle-shaped.
The rock is first cut into a slab, with the thickness determined by the planned project size. You draw the outline of the finished project on the slab. You can use a template for jewellery settings, or you can draw it freehand if you need a specific setting or size.
A diamond trim saw cuts the stone close to the outlined size, and a wheel grinder finishes the outline. The cab will be flat on top and bottom from the slab saw, and flat around the outlined edge.
You will mount your cut cabochon onto a dop stick, using a wax base. For a small project, mount the cab to the dop stick after drawing the outline in order to protect your fingers from the grinder. Hold the stick as you shape the stone against the grinding wheel. The process begins with a rougher grit and switches to finer grits as the piece gets closer to the final finish size and shape.
The finishing of a cab involves sanding and polishing. Sanding takes off scratches left by the grinder and does the final shaping. Sanding goes through several grit sizes, too, with the stone looking more finished each time. You will polish the stone on a softer, padded surface, using a paste of cerium oxide or tin oxide, to brighten the finished cabochon.
Transparent and crystal gemstones are cut with intricate and beautiful facets. These gemstones are "lapped" on a flat disk that is impregnated with diamond chips, again using different grit sizes. The machines have angle settings, index gears that adjust the rotation of the stone, depth control, speed control and lubrication. You mount the stone to the machine's dop stick with wax, then mount the stick to the machine. This is called the quill.
Faceting is a slow process, as one cut that is too deep or an angle that is slightly off can ruin the final product. Beginners learn to cut and facet gemstones with glass or quartz since that is more cost-effective than making a mistake with an emerald, for instance.
Sculptures and other art
Gemstone sculpting uses the same diamond-impregnated saws, grinders and faceting machines, but the artist often customises the machine for his or her own style.
Machines make beads or form animals or other shapes. Freeform art sculptures can take any shape. You can sculpt softer rocks and minerals with hardened steel tools, which are much less expensive than the diamond tools needed for harder materials.
You also can make mosaics with tiles cut from gemstones or from scrap cuts made when cutting the rock for other projects.
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