How to Make a Cabochon | CRATEX Abrasives
This article is part of Silicon Carbide Lapidary Grinding Wheel series.
For full article click here
Chapter 1 of this article already mentions cabbing or cabochon cutting as one of the four basic lapidary arts. Cabbing is also the most popular lapidary art of the four, probably because pretty much anyone can master it. All you need is some basic lapidary equipment, creativity and patience, and soon you'll be on your way to create neat cabochons.
"So, what is a cabochon?", you'll might be asking now. We are positive that you know what it is, it's just that you perhaps never heard what it's called.
Cabochons,or "cabs" for short, are small mesmerizing stones most commonly used to make stunning jewelry pieces, such as necklaces, earrings, bracelets or cufflinks. They can be cut and shaped into many different shapes – ovals (most common shapes), hearts, squares, rectangles and any other free-form shapes. Familiar now?
You probably are, but also your next question might probably be: "But, isn't a bunch of these stones already available for purchase?" And the answer would be - yes. However, in case you've ever thought that it would be so cool to custom make a stone for your own jewelry, or that a custom-made cabochon stone would be an amazing birthday present, then you've already heard gentle whispers of lapidary.
Besides, creating these beautiful cabs from slabbed rocks on your own is a truly rewarding process, and we are positive that you'll be hooked before you know it.
From Slab to Cab: Step-by-Step Guide
This will be a simple 10-step guide to creating your very first cabochon. We strongly suggest that you never start with your precious slab. Only after you get some experience and get to know your equipment it's time to exchange your practice piece with your special slab.
As a complete beginner, you'll probably wonder how long each step should last, and sorry to disappoint you, but there's no exact calculated must-time. The closest estimation would be – stay on each step until you've eliminated scratches from the previous step (grit). And don't dwell on this – you'll get a solid sense for grinding necessary on each step over time.
The most important thing is to follow the safety precautions presented in Chapter 5 and to go through the user guide before operating any machine.
Step #1: Select Your Material
There are a lot of different stones out there. Their most important characteristic for you as a young cab cutter is their hardness, b
ecause the hardness will determine cabbing techniques that you are going to use. A smart idea would be to get yourself familiar with the Mohs Hardness Scale , as knowing your gemstones will help you reach the best possible results by choosing the right grits for sanding and polishing.
There are two ways for getting a slab: going to a rock mine, which is really fun, but not for everyone, or purchasing pre-slabbed rocks online or at a local rock-shop. Regardless of what you choose, there are a few guidelines at this point that you should follow.
1) Check both sides of the slabs to make sure there aren't any fractures, cracks or pits, because these damages could cause the stone to split during the process;
2) Most cabs are made from 1/8"-1/4" slabs, but always make sure you pick the size and thickness that will match the size of the cabochon that you want to create;
3) Choose slabs that have interesting colors or patterns, because these are the features that you're going to bring out during the process. There are a few neat tricks to help you visualize the finished piece – either wet the material or hold it up to the sun, as this will give you an idea about their potential and what
they're are going to look like polished;
4) Harder stones tend to take a nice polish easier than softer stones, so you'll probably have more success if you use harder stones initially.
Step #2: Create a Specific Outline
First, you'll have to decide if you are going to cut one or multiple cabs out of a single slab. If you're going for the multiple, make sure you leave enough space for trimming and grinding between the shapes.
Next, before you begin cutting, you'll need to mark the outline of the cabochon's shape. Cabochon cutting template is quite useful for beginners and we suggest you start with ovals or circles, as these are the easiest shapes.
Inspect your material – if it has a solid color, you can place the template anywhere you like. However, if it has a pattern, catch it with the template. Just keep in mind that the stone will change as you round the top, so inspect it some more to get an idea about how it's going to change.
After you decide on the best possible area, run a fine-point permanent marker, an aluminum pen or a brass marking stylus around the inner edge of the template. Don't use a pencil as it will get washed away, nor a liquid ink, because many gems will absorb it and create a mess.
Step #3: It's Saw Time!
After you're done with making an outline, it's time for the trim saw. You'll need to cut away as much excess material as possible, leaving as little as possible for the grinding, sanding and
polishing operations (about 1/16" to 1/8" of space).
Until you become comfortable enough to cut the material off freely, a good idea would be to draw saw guide lines. These are different from the cabochon outline – while the cabochon outline represents the oval shape of the cab, saw guide lines are straight lines around it that make out a rough octagonal shape or a rough cabochon. Here are a few tips for this step to maximize the results:
1) Cut the slab as closer to the outline as possible to maximize the rough remaining, as it can be used for other cabochons, tumbling or inlay beads;
2) Don't ever try to cut curves with a saw blade, only straight lines;
3) Always have the coolant flowing before you begin to cut, as it will lubricate the blade and keep the working area debris-free;
4) A band saw provides an accurate cut, so it would be an excellent alternative that can minimize the grinding step.
After you are done trimming, wash your cabochon in a warm, soapy water to remove dirt or oils.
Step #4 (Optional): Dop, dop, dop
While unnecessary for larger cabs and highly experienced lapidaries, this step is a great method to use if you are about to grind or polish smaller cabs that are under an inch.
Dopping basically means securing your cab to a 4-5" wooden stick, called the dop stick, with a special dop wax. You would place the stick into the wax, spin it to pick up the wax, and press it on the back side of the cab. After you blend the wax, you would return the rick with the cab to the heater for a few more minutes.
Having your cab on a stick while grinding or polishing ensures visibility, provides control and precision while keeping your fingers safe. Here are a few tips to ensure you are doing everything right:
1) Make sure the cab is clean and dry before you dab it;
2) Make sure you warm the cab as well, as it will provide a more reliable bond. Bad bond will cause the cab to be thrown off the stick;
3) Make sure you dip your fingers in cold water if you need to shape the wax to secure a stronger bond. Otherwise, you'll burn your fingers;
4) Always test the bond between the cab and the dop stick after they cool down and before you grind.
Step #5: Proceed with Rough Grinding
Rough grinding means rougher excess material removal left from the trim saw or removing deeper irregularities to prepare the surface for polishing and smoothing operations. Of course, in case
you went for a harder material (e.g. agate), you'll start grinding with the coarsest grinding wheel , and in case you are working with a softer material (e.g. opal or turquoise), you'll start with the softer one.
It needs to be said that this is probably the hardest step of cabbing, because this is where you'll need to create that properly domed surface on the face of the cab. This is done by making sweeping, J-shaped motion starting at about 45°, while pulling the cab towards you and turning it for about ¼ as you go.
After you are done with rough grinding, clean and dry the cabochon and inspect it. The scratches much be shallow enough to be completely removed by each following step. Some of the important things to consider at this point would be:
1) If you notice that the grinding wheel cuts too slowly, go for a coarser wheel. Important is just to start gently to avoid irreversible mistakes;
2) Always start the coolant before you turn on the machine. If you see a powdery residue, the coolant flow is not enough;
3) Always grind below the centerline. In case you grind above it, the cab will be yanked out of your hands and sent flying across the room;
4) Grind down towards the marked outline, but make sure you leave enough space for the following steps;
5) Use an additive for rust prevention unless your machine is entirely made of stainless steel.
Step #6: Proceed with Fine Grinding
This is where you'll begin to use progressively finer-grit wheels to shape the cabochon and remove the scratches. You'll start with fine or ultra-fine grinding wheel of about 220 or 325 grits and applying light to moderate pressure while regularly inspecting the progress. You'll continue with the same motion, as you'll need to continue to refine the shape.
Here are a couple of things to keep in mind during this step:
1) Make sure the cabochon is symmetrical and it is curved the way it is supposed to;
2) Make sure the coarse scratches from the previous step have been removed, or you'll end up with a low-quality finish.
After there are no more coarser scratches, you are ready to proceed to the next step.
Step #7: Now You Sand & Smooth
This is the step that comes only after you are satisfied with the cabochon's shape. The grits that you
are going to use depend on the type of the wheel material. For example, if you are using a diamond wheel, you'll use the 600 or 1,200 grit, and in case you are using silicon carbide wheel, you'll use 600-grit.
At the same time, the grit will depend on the type and hardness of the rock, so, for example, 1200-grit would be fine for agate, but for softer gems you might need 3,000 or even 8,000. The cabochon should start to have a satiny appearance at this point.
The final fine sanding or the pre-polish is what the quality of your polish will depend on. After you are done, the surface must be completely smooth with no visible scratches whatsoever. If the surface is not ultra-smooth, you won't get a high polish.
Important tips for this step would be:
1) Make sure you thoroughly wash your hands and the cab before you start, as any harder grits left by the previous step could cause deeper scratches which will be impossible to polish out;
2) Make sure the cab is completely dry if you want to see the true progress of the operation. Your hands would need to be dry as well before you begin drying the stone;
3) If you can still see the scratches or scales, it means that they are too deep to remove at this point. Go back to previous grit and start over.
Step #8: And Now You Polish
This is the part where your cabochon is going to get a high shine and it includes soft polishing pads, such as canvas pads, leather pads and felt pads, and polishing compounds.
Most common polishing compounds used in lapidary work are diamond paste (excellent on ruby and sapphire in combination with leather or special pads), chromium oxide (best on jade in combination with leather or felt pads), tin oxide and cerium oxide (best on quartz). On the other hand, aluminum oxide used on suede would be the most versatile method that will put a high polish on more cabs than any other method.
After you charge the pad with the polishing compound, begin polishing. You won't use drip water, as it will wash away the polishing compound. Rather, you'll polish and then periodically rinse the cabochon with clean water to lower the temperature and dry it to track your progress.
The running speed will depend on the type of the material, the size of the cab and your ability to control the dip stick in case you are using it. Rock and rotate the stone, work up and down over the center using medium pressure. As a rule, harder cabs will have a higher polish, while softer cabs will have a nice satiny finish. Continue until you've reached the desired level of polish.
Important lapidary tips for the cabochon polishing step would be:
1) Make sure the cabochon is thoroughly washed before you begin;
2) Rinse and dry the flat lap reservoir and master lap to remove any grits left by the previous steps before you begin;
3) Wet the pad with water, but always turn it on briefly to throw off excess water before you begin, as the pad needs to be damp;
4) Be careful with the polishing compound – only a little bit should be sufficient;
5) Since the polishing wheel will run at a much faster speed than it does it the previous steps, the polishing operation will create a lot of heat, so be careful with stones such as opal, as the heat can destroy them.
Step #9 (Optional): The Finishing Step
This is the step that you're going to take in case you've used the dop stick. The best way to separate your cabochon from the dop stick is to put it in a freezer for about 10 minutes. After the 10 minutes are up, you'll be able to easily separate the cab from the stick.
The dop stick will be reusable, and the remaining wax can be carefully scraped away with a knife. To remove film from the wax, simply use a tissue or any other soft paper and alcohol.
If the back of the cab won't be seen because you plan to incorporate it in jewelry, then you won't need to polish it. However, if you want to polish the back as well, you'll need to sand and polish it and repeat the cabbing procedure. You'll just attach the cab back to the dop stick, this time either to the top side or the front.
Step #10: Judge Your Cabochon
One thing's sure: at Step #10 you should be really proud of yourself. Inspecting and judging your cabochon is only a way of recognizing points of possible improvement and getting ready for the next round.
First, you'll inspect the polish. If there are scratches or pitting, the light reflection from the surface will be reduced. On the other hand, a mirror high-polish on your cabochon will make all the effort seem worthwhile.
Next, take a look at the shape, look from both sides and both ends. There should be an even curvature with mirror image from side to side, with no visibly ticker areas anywhere and no bulging. If the surface is properly cut, you'll be able to see an equally reflected glide all over, but if not, the light will begin to shake.
The last thing to inspect is the top of the cab. Hold it against the light, and if the light doesn't flow smoothly, the area is flattened, so the neither cutting not the polish weren't properly done.