What to look for when purchasing a stone.
Educating yourself about the cabochons and gemstones you are purchasing online or in person will help you make good purchases and avoid disappointments.
Let's talk about what to look for when buying a cabochon.
Educate yourself about the material you are looking to purchase. Understanding the properties like hardness will help you choose the right stone for your work.
Look for listings that show several views of the stone. You will want to see front, side angles and the back. Don't be afraid to ask the seller to provide more images if you are unsure. Videos are great for seeing polish and all views of a stone.
Shape. How even is the contour? A cabochon should have an even curvature to its surface. Look carefully at the cab from both ends and both sides. The shape (the curvature) should be a mirror image from side to side. No area should be thicker than its opposite. There should be no bulging. Look for flat spots by examining the stone from all angles. Some material lends itself better to a flat top. If the stone is cut with a intentional flat top look for evenness there as well.
4. Sides- Look at the sides of the stone.A well cut cabochon will have slightly sloping angles with the bottom slightly larger than the top. Typically about a 60° angle on domed cabochons is standard. Some cabochons are cut with 45° straight sides, this is perfectly acceptable and can be fun to set, either in bezel or prong setting. If you are setting your stones a prong setting look for fully polished sides. You may find cabochons that are partially cut leaving a portion of the cab with the natural "ring" edge. Regardless of the cut the sides of a cabochon should be polished.
5. Back - Look at the back. Is it level and flat? Is the back edge beveled? This prevents chipping when setting the stone. Is the back polished? Again if setting with prong or open back settings a polished back is preferred.
6.Polish. When examining a cabochon, look closely at the polish. Look for any scratches or pitting that will reduce the amount of light reflected from the surfaces.
Move the stone so the light travels across the top. If the surface is properly cut, you’ll see the band of reflected light glide evenly over its surface. The band of light will begin to snake if there are any irregularities. If purchasing online, viewing the stones at many angles will be crucial to establishing the polish.
NOTE on polish: Not every material will polish to a mirror finish. Understanding the material you are looking to purchase will help you make a good purchase. If you are not sure about the stone you're buying ask a professional.
High Polish. Material with a high hardness (Mohs scale) will take a very high polish. These include agate, chalcedony, jade and many jaspers and petrified woods. However turquoise can be highly polished as can ivory. Most jaspers will polish very well.
Glossy Polish. Some materials are soft making it difficult to get a super high polish, these include dolomite, serpentine, Maligano jasper and a plethora of other materials.
Natural surface material. More lapidary artists are creating natural surface cabochons. Some material like Lapis, Aquamarine, Tiger Eye are quite beautiful with a naturally cleaved surface.
Matte finish. Many stones are quite interesting with a matte finish. Materials vary.
Buying stones is so much fun and it's even more fun when you know what you're doing! With a veritable galaxy of options out there you need to be informed. Use the guides here on Addiction to help and consider a course such those offered by the GIA or join your local gem and mineral club.
Enjoy and Good Luck!
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