Filling an Empty Space and Enhancing a Cabochon

By Bob Rush

I often look for a special feature within a slab when choosing the shape to cut into a cab. When the slab has a uniquely shaped opening caused by the method of infilling in the rough, I always try to incorporate it into the cabochon, especially when it will enhance the piece.

The plume agate pictured had a very interesting vug with a botryoidal inner surface. Finding these features when you are slabbing a particular rock is often an accidental occurrence, but it is a plus. I designed the cab so that the vug was positioned horizontally near the bottom, and it ended up well suited for my cab.

Obviously, wearing this cab as a pendant would not be the best choice because the background, whatever it is, would detract from the cab. Also, the cab’s translucency detracts from its potential beauty, so I decided to install a backing on the cab. My preferred backing is basanite, a black basalt. It is quite durable and takes a great polish.

Even after selecting and polishing the basanite, there was still a void in the piece’s lower right side. I decided to embed a small round stone to fill the void. I struggled a bit in selecting the material to use, as I wanted something to enhance the cab. Then I remembered I had a few small fire agate pieces that might do the trick, but many of the pieces are very directional in their color pattern. I needed a piece that would exhibit its best color when it was hanging as a pendant. This necessity narrowed the choice of available pieces to just one. As I was grinding and polishing the piece, I rotated it under the light to make sure it would show well in all orientations. It did have some slight issues regarding orientation, but I made sure to mount it in the ideal position.

I used diamond wheels to recess the basanite area, where I intended to mount the fire agate. The basanite layer on the back of the cab is 3mm thick, so I recessed the stone 1-1/2mm. I wanted this recess to ensure the durability of the adhesion on the fire agate cab.

As I was applying the epoxy 330 adhesive, I had to be careful to keep it out of the “window” area of the cab so it wouldn’t detract from the beauty of the stone. I think the final appearance has a Halloween jack-o-lantern look to it.