HOW TO RESCUE A CAB PREFORM
As I was searching through my piles of slabs and such for something new or di erent I came across a large Brazilian Agate preform that I started working on a few years ago. It isn’t unusual for me to have partially completed pieces scattered about. is particular piece had a surface fracture that I thought I could grind out as I was shaping the piece. It turned out that the fracture was deeper than I thought so I had set it aside and essentially abandoned it. When I started to reexamine it, I saw that I could rescue the piece if I could somehow cover the fracture.
In the past, I have inlayed small cabs as an accent piece, so this was a starting point for this project. I wanted something that would be eye-catching but not compete with or overwhelm the main pattern in the cab.
FIRE AGATE INSPIRATION
Lately, I have been working on some re agates. ey do present challenges because of their shapes and surface patterns. You mostly have to use some carving techniques to access and expose the very thin color layers.
Typically, this material has a white or clear layer covering the brown-based color layers. Aer the top layer is removed, botryoidal color bubbles require careful, slow grinding to expose them. You also have to carve away the material between the color bubbles to expose the colors on the side of the bubbles. All of this work is much di erent than standard cabochon work. Accessing all of these color features means the nal shape of the cab will have an irregular outer shape. Setting these cabs requires advanced skills in metalwork, However, on rare occasions, the patterns will allow you to make a common or regular shaped cab.
MAKING A SMALL CAB TO FIT A LARGER CAB
In my current situation, I was able to nd a re agate with a pattern that allowed me to make an oval-shaped cab that was easier to inlay into the larger cab.
I started by using a small oval template to mark the desired location of the re agate cab. Because I had
nished shaping and polishing the larger cab, my ne point sharpie wouldn’t mark on the cab. I had to sand the area on my cabbing unit with a 220 grit belt to make a suitable surface for marking the re agate location.
I mounted the cab on a dop stick to make it easier to manipulate as I was checking for a good t during the hole grinding steps.
FINISHING UP
My rst grinding step was done with a small diamond round bur to quickly remove most of the material. e next material removal was done with a small diamond cylindrical bur.
e nal material nishing and shaping was done with an inverted cone diamond bur. is step took the longest because repeated tting checks had to be done slowly and carefully. e nished depth of the mounting hole was 2.5mm.
I wanted the inserted cab to have a more nished look so I fabricated a scalloped silver bezel strip which had to be accounted for during the nal nish tting. I attached the inserted cab and bezel with epoxy 330.
As I view the nished piece, I’m happy with the rescue.
Bob Rush has worked in lapidary since 1958 and metal work and jewelry since 1972. He teaches at clubs and Modesto Junior College. Contact him at rocksbob@sbcglobal.net.