by Bruce Frymire Apr 03, 2018
Cutting and selecting material for my cabochons.
Upfront I want you to know that not all cabochon material will produce a finished product that will be free of pits, fractures or inclusions. Regardless, when I follow my guidelines found in this article I end up with a beautiful cabochon that I'm proud to use in my jewelry. If I have to leave in some tiny pits or very small fracture lines I make sure that this inherent look will add to the beauty of the cabochon, if not I will try and remove them.
A little about how I like to get to my end result which is a cabochon with a great looking finish.
I start with rough material and cut it into slabs, 5-8 mm thick, this is done with a diamond lapidary saw blade.
- I then eyeball all the pits and fracture lines in the slabs and mark them for reference.
- Next, I will mark out the areas that don't have any of pits or fractures. A variation to this rule, if the material is scarce or rare and the material is prone to have pits and fractures I may have to leave in a few that will be seen in pictures but very hard to see in hand. I will point them out in my descriptions.
Taking care of pits and fractures
After I cut out the areas outlined in my slabs I use a 10 power loupe to detect any pits and fractures that may show up in the pictures and might possibly take away the beauty of the cabochon. If any facial fracture crosses the front I will eliminate the fracture by re-cutting the cabochon. Some fractures and pits are so small they are hard to see even with a 10 power loupe, after the final polish they may show up so I will point them out in my write up or I may even start over because I don't like how they look.
I don't normally use epoxy to hide pits and fractures unless the material is so rare it warrants it, or the customer wants me to fill them in. My description will point this out if epoxy was used.
Shaping the material
I use what they call a flat lap grinder/sander, mine is from Ameritool-Inc. In the first step I shape the cab using metal flat discs electroplated with 100-600 diamond grit. In subsequent steps I use resin discs impregnated with 325 to 1200 diamond grit.
I finish each grinding step with a light touch and only move the cab in one direction which creates grit lines running in one direction. This is important because after using any subsequent disc I end up sanding the cab in the opposite direction from the way I did with the previous disc. I look to see if there are any crossing lines. If there are I continue with the current disc until all previous lines are eliminated. At this point and before I use the sanding discs I closely look at the center top of the cab, this area shouldn't have any crossing lines. I will continue with the current disc until they are gone.
I use flat lap resin coated discs that have been impregnated with 325-1,200 diamond grit. Sometimes in order to remove the finest of grit lines I may use white polishing pads with 8,000-50,000 diamond grit polish.
In these steps I start with a resin flat lap disc that is impregnated with 325 diamond grit, finish the 325 going in one directions and using a light touch. Like before I will check to see if any previous lines are visible and remove them using the current disc.
My next disc is the 600 grit sanding disc and after finishing with the 600 I will again check for previous lines. If I find them I go back to the previous grit. If I don't find previous lines but I can visibly detect 600 grit lines I will continue on with my finest sanding discs, 1200-50,000 grit. I work each grit the same as I did with the previous sanding discs.
The cab is ready to be polished when there are no visible lines. Polishing the cab will show any areas that I missed in the sanding steps, when I find them I have to go back in steps to remove them. To get a mirror shine all grit lines have to be removed, especially on the face of the cab. The sides and back will also be given my best effort.
Polishing my cabs
I use a special mixed paste to polish all my cabs. The polishing paste does contain a fine grit so faint lines and imperfections should be eliminated in the polishing step. I should end of with a mirror polish on the face of the cab with the exception of some material that only produces a bright luster. This info will be given in the description.
Back of my cabs
I believe in finishing the backs of all my cabs. I grind and sand the back to the 600 grit maximum and polish until I have a nice luster or shine. Sometimes not all pits and open fracture lines can be removed from the back or sides, if they look like they may go too deep I may have to leave them in. I do try and remove all girt lines.
If your plan is to wire wrap your cab you will find that the finished back will delight your customer because they will be able to show off their jewelry front and back.