Artists have been cutting into gemstones of all kinds for eons. And they’ve used the widest array of gemstones imaginable for displaying their artistic prowess. When the gemstone is composed of several colored layers, its all the better. A multi-layered stone allows the skillful artisan to portray a sense of depth into the carving. For this type of dimensional work, natural conch shells and agate work best. But daring designers have also used onyx, malachite and black opal for years. Cameos in these stones pop up regularly for sale with top auctioneers.