Cabochon Making 101 - Part II
Cabbing with Tucson's Old Pueblo Lapidary Club
While cabbing is definitely "hands on" work, here's where that dop stick comes into play. It gives you something to grasp and manipulate the cab with, and saves a lot of wear and tear on the fingernails. If you know what you're doing and have the physical strength to press hard continuously, you can really hog off material fast on one of these heavy duty 8 inch grinders spinning a 100 grit diamond wheel. Of course, if you don't know what you're doing, that means you can also ruin a cab in pretty short order too. :-(
As the cab is rotated with the dop stick, a sweeping, oscillating motion is used to keep the contact point moving on both the cab and the wheel, the object being to produce a smooth and properly domed surface on the face of the cab (and uniform wear on the wheel). For me, this motion was the most difficult part of cabbing to learn. There's a certain feel to things when you get this motion and the pressure correct that's hard to describe, but you soon come to know it when you're doing things right. It's a skill that's refined with experience, although I only had to destroy a couple of rocks before I got the basics down on ovals and felt ready to try my hand at some free forms.
I just use light to moderate pressure and inspect the progress and results of various motions frequently. Once you're started it's a closed loop process and you quickly learn what works for you and what doesn't. Since I've been using inexpensive materials and the time involved is relatively low, I consider them expendable and it's not a heart breaking ordeal to screw one up as part of the learning process. The experience of only half a dozen or so cabbing sessions has changed the grinding operation from feeling awkward, clumsy and vexing to relaxing and therapeutic. I like to think of cabochons as faceted stones with infinitely many meet points...
It took about half an hour on the diamond grinder to grind the dome on this cab. I worked the
stone progressively from the edges towards the center of the face. There's a tendency to grind down the corners on a freeform like this too much and that's where the reference line helps to give a reality check.
If you're having trouble seeing what's going on, one technique which can be employed is to black out the problematic area with a magic marker and look to see after some passes on the grinder if
you're taking off material only where you intended to. The grinding operation is complete when the stone is fully shaped.
The next step is sanding with a 220 grit carbide belt on a water cooled sander with expandable rubber drums. The 220 grit belt is used to remove the scratches left in the surface of the cab by the 100 grit diamond wheel. The 220 grit belt is also abrasive enough that it can be used to do some of the fine shaping and smoothing, especially with softer materials. The rubber drum compresses and conforms to the face of the cab as pressure is applied against it, which also helps with the smoothing chores. The same sweeping, oscillating motion that's employed during grinding is also used on the sanders.
The cab must be frequently dried by wiping it with a paper towel or rag during sanding to reveal
the remaining scratches. When only 220 grit sized scratches remain, the work is moved to another sanding station equipped with 320 grit belts and the process is repeated to remove the 220 grit sized scratches. This process is repeated yet again at another station with 600 grit belts.
When all of the 320 grit scratches have been removed and the cab is dried, it has a smooth sheen and a hazy, semi-polished appearance.
The cab is almost finished at this stage and the next operation is polishing. A rotary
polisher with pads to hold the polishing compound is employed for this task. The pad is wetted
with a spray bottle, and then a paste of some well recycled cerium oxide is applied to both the cab and the pad. The face of the cab and the edges are then simply pressed into the pad
and polished all around. As the pad dries out, the cab starts to get draggy on the surface and it is at this point that the best polishing action seems to occur. Heat from friction can build up quickly during polishing, and it's important to let the stone cool frequently so that
so much heat is not built up that the dop wax softens and loses its bond to the cab.
The pad on the other side of this polisher is used with tin oxide, which gives a better polish on some materials than cerium oxide. The polishing paste tends to build up in any fine cracks or pits in the cab's surface, and it can be removed by a final scrubbing with a toothbrush and soap and water.
Finished! Ain't it pretty? All that's left to do now is to stick it in a freezer... this causes the dop wax to become brittle and lose it's bond to the cab, which often falls off under its own weight after a few minutes of cooling. Any remaining wax on the back side is then cleaned up by scraping with the blade of a pocket knife. Not too bad for a free stone cabbed by a mineral collector, huh?
There are many clubs and societies oriented towards lapidary and they offer unparalleled opportunities for newcomers to the hobby to learn and acquire lapidary skills and knowledge. One of the greatest things about the rockhounding hobby is that there never seems to be a shortage of teachers and mentors who are willing to spend the time to help, teach and advise those with less experience.
Another not insignificant advantage to exploring lapidary through a club is that they often
possess and make available to their members many thousands of dollars worth of equipment, the purchase of which is a major obstacle and deterrent to many beginners.
I already owe a deep debt of gratitude to OPLC and some of its members for the opportunities to learn about and enjoy lapidary they have made available to me. If you're interested in lapidary but haven't got your hands wet yet, I can't encourage you too strongly to seek out and join a local club if one is available to you.
If you're a Tucson area resident or snowbird, you're welcome to join us! The Old Pueblo Lapidary Club is a non-profit organization dedicated to the maintenance, development and improvement of lapidary and related arts, including the earth sciences.
In retrospect, if I'd just thought it through, I'd probably have gotten involved in lapidary
as a suitable hobby years ago. I've always enjoyed creating things with my hands and using tools to do precision work. I've come to appreciate that one can do some pretty amazing and fun stuff to rocks with lapidary tools, and dare I say it - even improve them over their natural state.
I've decided that if I like a rock better after working on it, that's all that matters! And if I don't - hey, what the heck - At What Price Art?
Cabochon Making 101 - Part I
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