by Bob Rush
March 2012
One of my favorite stones is carnelian agate,” says March Lapidary of the Month Bob Rush, of Valley Springs, California, “especially when it is set in silver. I wanted to make something that used multiple cabs of this agate. I also wanted to do something that utilized a wax pen and a special formula of highly flexible casting wax to ‘draw’ a design. This decorative box project fulfilled all those requirements.
“I started by making a sketch of the box that was close to the final size so I could determine the shapes and sizes of the cabs. The dimensions of the box are 3½ inches wide, 2 inches high, and 2 inches deep. I wanted all the cabs to be as similar to each other as possible. I was able to find a large enough slab of Brazilian carnelian agate from which to cut all of them.
“Next, I needed to find something that I could use as a form to ‘draw’ the box on. I had a block of glass that would work perfectly. I started out by drawing a wax design on the outer perimeter of the back of the largest cab, which was going to be mounted in the lid of the box. This first line of wax would become the seat for the cab. I used this method on all the remaining cabs.
“Next, I started drawing the prongs from this seat up over the cab, keeping the spacing nearly equidistant from each other. After finishing this, I placed the cab on the center top of the glass block and started the web pattern that was to be the top of the box. Next, I drew a continuous line around the outside of the uppermost area of the glass block, ¼ inch below the top. This would be the lower edge of the top frame. I incorporated the small cab into the latch.
“I started locating the cabs around the perimeter of the bottom area by establishing the seat for the front cab, adding the prongs, and locating the cab on the block. I drew the web pattern around it, then proceeded to do the remainder of the cabs on the sides and back. As I filled in the bottom pattern, I added four small balls to the pattern, one in each corner. These were to be the feet for the box.
“The final step for the wax work involved shaping the wax to make two hinges for the lid and receiving tabs on the lower section. The final step before casting was to remove the cabs by flexing the prongs away from the cabs and labeling each one so I would know where they were to go during the assembly steps. The special formula wax that I use has a lot of plastic in it, so the entire wax pieces are very tough and flexible.
“Next, I attached sprues to the top piece and the bottom piece. I placed the pieces in the casting crucible, added investment, burned out the wax, and cast the pieces in a centrifugal casting machine. After the pieces were cleaned and polished, I drilled the hinge tabs for a pin. The prongs for the cabs were bent back to create the opening for the cabs. The cabs were positioned and the prongs were bent over them. I gave everything a final polish, installed the hinge pins, and hammered over the ends to hold them in place. This project turned out just as I had hoped it would and I was quite
pleased with the results.”
