Creating A Decorative Feature
This column outlines a step-by-step project to create a decorative feature on the back of your cabochons using small burrs that mount in a flex shaft. It involves using diamond ball burrs of various grits and homemade wood burrs.
The first step is to select a translucent area on your cab or slab that shows considerable transmission of light and color in the place where you will make the decorative feature. Mark a point with a felt tip pen and start the hole with a small coarse grit 1/8-inch diamond bur. I do the carving in a shallow plastic bowl cut from the bottom of a large plastic bottle with ½-inch of water inside. Dip the piece in the water and grind with the burrs for a few seconds and dip again.
Using a ½-inch diameter coarse burr, continue the grinding by holding the side of the bit in the previously made hole. Continue dipping and grinding for a few seconds. Every few minutes, turn the burr vertically and correct the shape of the hole because when you grind with the side of the burr, it pulls slightly sideways. Ball burrs do not grind very well if you hold them vertically.
As you are grinding the hole, stop and look at the back of the piece under a strong light to see how it appears. If you like how it looks, begin the sanding steps to remove the grinding marks.
Shape some 1/2-inch diameter 1/2-inch long wood dowel pieces to match the hole size on the piece. Cut the dowel into ½-inch long pieces. Locate the center end of the dowel piece and drill a small hole into the end using a 1.5mm drill bit. Mount the dowel piece on the screw mandrel and shape it with a coarse file while spinning it in your flex shaft handpiece. Check it frequently for the correct shape to match the hole in the agate piece.
Make two more just like it. You will need three of these, one for the 220 grit, one for the 400 grit, and one for the polish step.
For the first sanding step, use 220-grit tumbling media. Mix the grit in a small, shallow condiment cup with a small wooden spatula and water to make a thick slurry. Add only enough water to make the slurry about the consistency of toothpaste. Using the spatula, scoop some of this slurry into the hole on your piece. Wet the wood bur and push it into the hole rather firmly to embed the grit into the wood. Run the flex shaft unit slowly and move the wood bit around a lot, including the hole’s sides. Stop and add more slurry when the wood bit starts squeaking. Repeat this process a few times. Stop and wash out the slurry and check for how well the sanding has removed the grinding scratches. The hole should start to look somewhat shiny.
Repeat this step with a new wood bit dipped into water and the 400-grit media. The hole should be even shinier after this step.
Wash everything very thoroughly and do the same process with a cerium oxide slurry. You should get a very well-polished hole after a few minutes.
SUPPLY GUIDE
I get the diamond bur sets from Jadecarver. com. They come in a graduated 14 piece set and six different grits. The screw point mandrels have a ½-inch length thread, and the shank diameter is 1/8 inch. They can be found at Rio Grande Supply.