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Cabochon Making 101
Cabbing with Tucson's Old Pueblo Lapidary Club
Article and Images by Bob Keller
http://www.rockhounds.com

While I have been involved with mineral collecting for some time, I've just recently begun to explore the world of lapidary and its attractions as a hobby. I hate to admit it, but somewhere along the line I had picked up a bit of an elitist "attitude" towards lapidary and the poor, misguided, rock grinding, "grunt" rockhounds, who had weird and peculiar ideas about improving rocks by cutting them up and grinding and polishing on them. I was a mineral collector, not a rock butcher! I guess I figured if God had wanted man to mess with his rocks we'd have been given a lot harder fingernails...

However, it would seem that God gave us carbon in various forms and the brains with which to develop technology. I guess it was inevitable that brains + diamonds = lapidary tools. Well, I've finally seen the light and been converted through my involvement with Tucson's venerable Old Pueblo Lapidary Club. In addition to their ongoing faceting, lapidary and smithing classes, OPLC conducts open shop sessions, giving the members access to and use of the outstanding club workshops and equipment. I've been having so much fun making cabochons there that I thought I'd bring some of my fellow mineral collectors along for a session and share a little of what I'm learning and enjoying.

Here's some views of one of our shops. This room houses OPLC's lapidary shop and contains equipment and tools used in cabochon making such as diamonds saws, diamond grinders, carbide belted sanders, and polishers. Other rooms in this club owned building house our metal smithing and jewelry shop, the faceting shop, and a saw room.

I've decided I need a couple of bola ties as accouterments to my wardrobe. Of course, since my conversion to a rock grinding grunt rockhound, I had to make the cabs for these myself. As you can see, OPLC is very facilitating for members with such inclinations and aspirations.

After finally accepting that a 200 carat faceted gemstone was likely to be regarded by many as a bit too gaudy for a tasteful bola, I selected this slab of chalcedony as a promising piece of rough for this project. I'm saving the 200 carat gemstone idea for a future one. ;) I'd like to say I field collected this rough as I was told by another club member that it was a slab of a Brazilian agate, but the fact of the matter is I found it in a box of scrap, discarded and donated material under one of the workbenches in the lapidary shop. There's enough material in that box to make many dozens of cabs. You don't even need to bring your own rough to get started cabbing with OPLC!

Here's a few of the templates available in the lapidary shop for marking out cabochons with various standard and not so standard shapes. If you're going to marry the cab to a commercial finding designed to hold a standard sized stone, it's important to accurately cut it to a specific outline so it will fit. I'm not planning to use a finding to mount this cab, or if I do use one it will be custom made, which allows me to use a free form design for the outline. After studying the rough for a bit, I decided the shape of another freeform cab I had done was suitable and simply traced around it to establish the outline. The rough was just a little short in one corner, so it gets rounded a little more. It's an art, you know...

The next step is cutting the slab close to the desired outline with a diamond trim saw. On the saw table are both oil and water lubricated trim saws, the water saw being reserved for softer and porous materials which could be stained or discolored by oil. The slab is about a quarter of an inch thick. I would have preferred it to be just a wee bit thicker for a cab this size, but hey, the price was right.

I cut away the material surrounding the outline with a series of cuts on the oil lubed saw. This is messy business and relatively slow going with a feed rate of about an inch a minute. The metal blade that the diamond abrasive is bonded to is soft and easy to dork up if you're too aggressive with the feed rate or try to cut curves with it. However, it's still much faster and more economic to remove material with the saw than a diamond grinder, and I've learned a little extra time and attention spent here carefully cutting close to the outline with successive and progressive cuts is rewarded handsomely during the subsequent outline grinding operation.

After sawing, the cab and hands are both cleaned in a tub of oil absorbent media (commonly known as kitty litter), and then the cab is scrubbed clean of oil with an old tooth brush, soap and water.

The next step in the process is to establish a smooth and accurate outline with the grinder, removing any margins or small corners of material left over from the sawing operation. An 8 inch water cooled grinder with 100 grit diamond wheels is used for this as well as the subsequent basic shaping processes of doming and rounding the cab. Note the plumbing to supply the cooling water and the drain pipe to carry away the runoff. An ultimate embellishment would be a water heater inline to warm the incoming water so it wouldn't be as cold on the pinkies...

Because this cab has straight sides and a relatively large area to hold on to, I elected to shape the outline on the grinder prior to dopping it to a dop stick. A dop stick is used to hold and manipulate the cab during grinding, sanding and polishing operations. They're pretty handy to have mounted at this stage when you're making a round or oval shaped cab, and especially if it's of a small size.

A tapered outline, narrower on the face side than the back side, can be established at this point if the cab is to be prong or bezel mounted in a finding. It's also a quick matter to apply a slight bevel with the diamond wheel to the edge on the back side of the cab to help prevent chipping if the edges are going to be exposed.

Once a smooth outline and any desired bevels are applied with the diamond grinder, a reference mark is established around the perimeter of the cab. I marked this line at about two thirds of the slab's thickness and closest to the back side of the cab. This line is used to help judge the progress and facilitate uniform removal of material during the shaping process.

Prior to dopping the cab, it is placed on top of a wax heater to warm so the dopping wax will bond to it readily. It's important that the stone be clean and up to heat to get a secure bond. If this bond breaks while a cab is being worked, it's possible for it to be thrown by a rotary device and possibly broken or irreparably marred. It's also possible that you or someone else could get struck by a flying rock. Needless to say, the prudent lapidary wears eye protection while working with these tools.

The wax heaters are simply metal boxes with a light bulb inside for the heat source. These would be an easy home brew. Believe me, they get plenty hot. After the stone has heated up, a glob of dop wax is picked up and swirled on the dop stick, which is just a section of dowel about 6 inches long. It's then plunked down on the backside of the cab, and a finger can be employed to work the wax into a nice fillet.

The cab and dop stick are left on the heater for a few more minutes, giving the wax time to flow and bond. Then the assembly is removed and allowed to cool. The bond is then tested to make sure the cab is securely bonded to the stick. Once satisfied that all is properly prepared, the next step is grinding the face of the cab to a dome shape and generally rounding and smoothing it.

Sometimes there's rockhound traffic jams on frequently used equipment like the diamond grinders in the lapidary shop during busy sessions, but the congestion normally clears after several minutes as members move on to subsequent stages on their projects. I've learned to bring the material for several projects so that if a particular station that I need to use is crowded or full, I have something else to work on. That way I can stay as productive as I want.

I think one of the things that's appealing about cabochons is they're quick to make. I can often start and finish two complete cabochons, slab to polished cab, in the course of a three hour open shop session at the club. It feels like I got something accomplished when I leave the club at the end of a session with a couple of new cabs in my pocket. That is quite a contrast to my project progress in a weekly faceting class that I also take through OPLC, where I have literally spent months to produce a single gemstone.

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?