Introduction to Cabbing

Cutting a cabochon (often referred to simply as "cabbing") is one of the most rewarding skills a beginner lapidary artist can learn. A cabochon is a gemstone that has been shaped and polished as opposed to faceted. The resulting stone is typically flat on the bottom with a domed top, making it ideal for wire wrapping or setting in silver jewelry.

If you have stared at a rough rock and wondered how to turn it into a glassy, smooth dome, this guide will walk you through the entire process.

Cabbing machine wheels Modern cabbing machines utilize diamond-coated wheels of progressively finer grits.

Step 1: Selecting the Right Stone

Not all rocks make good cabochons. For your first attempt, you want a stone that is dense, lacks obvious cracks (fractures), and is not too soft nor too hard.

Optimal beginner stones include:

  • Agates (Crazy Lace, Plume, or Moss Agates)
  • Jaspers (Picture Jasper, Mookaite)
  • Obsidian (relatively soft but cuts smoothly like glass)
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Avoid highly fractured quartz, brittle minerals like fluorite, or toxic minerals like malachite (which requires heavy respiratory protection) for your first few attempts.

Step 2: Sabbing (Cutting the Slab)

Most cabbing begins with a slab—a slice of rock typically cut ¼ inch to ⅜ inch thick using a lapidary slab saw. If you don’t own a slab saw, many lapidary clubs and rock shops sell pre-cut slabs.

Once you have a slab, examine it closely. Wet it with water to see how the colors and patterns will appear once polished.

Step 3: Drawing the Template

Using an aluminum stylus or a specialized brass marker (standard pencils wash off in water), trace a shape onto your slab using a plastic template. Common beginner shapes are ovals (e.g., 30x40mm) and teardrops.

Move the template around the wet slab to frame the most interesting pattern (this practice is called "windowing").

Step 4: Trimming the Preform

You don't want to grind away massive chunks of rock on your shaping wheels—it ruins the wheels quickly. Use a trim saw to cut off the excess material around your traced outline. Leave about 1mm to 2mm of space outside your line.

Step 5: Dopping the Stone

Trying to hold a small, wet, slippery stone against a fast-spinning wheel is dangerous and exhausting. Instead, we use a dop stick.

  1. Heat dop wax over a spirit lamp or wax melter.
  2. Heat your stone slightly (wax won't stick to a cold stone).
  3. Apply a glob of melted green or brown dop wax to the end of a wooden dowel.
  4. Press it firmly onto the flat back of your preform stone.
  5. Let it cool completely.

Step 6: Rough Grinding (The 80 and 220 Wheels)

Put on your safety glasses and an apron! Lapidary is a wet and messy hobby.

Turn on the water supply to your cabbing machine. The 80-grit hard diamond wheel is for aggressive stock removal. Grind to your traced outline, ensuring the edges are perfectly vertical.

Next, move to the 220-grit hard wheel. Here, you will establish the bezel (the vertical edge around the bottom where the jewelry setting sits, typically 2mm high) and begin rolling the stone left and right to form the dome.

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Constantly move the stone. Pressing it in one static spot for too long will create flat spots that are difficult to fix later.

Step 7: Smoothing and Sanding (280 to 1200 Wheels)

Now you transition to the soft, resin-bonded diamond wheels. These wheels give slightly, wrapping around the curve of your cabochon to smooth out scratches.

  • 280-grit soft wheel: Removes all deep scratches from the hard wheels. Spend the most time here ensuring your dome is perfectly smooth.
  • 600-grit soft wheel: A matte finish begins to appear.
  • 1200-grit soft wheel: The stone will start reflecting light.

Dry the stone with a paper towel completely after the 600 wheel. Look at it under a desk lamp. If you see deep scratches, you must return to the 280-grit wheel. You cannot polish out deep scratches!

Step 8: The Final Polish

Depending on your material, you will finish on different media:

  • Diamond Paste on Leather/Canvas: Excellent for rubies, sapphires, and harder materials.
  • Cerium Oxide on Felt: The gold standard for polishing quartz, agates, jaspers, and obsidians.

Create a slurry of water and cerium oxide. Press the cabochon firmly into the spinning felt pad. The friction creates heat, which chemically and physically creates a micro-melt layer on the stone surface, resulting in a mirror-like gleam.

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Be careful with heat! Keep the stone moving. Excessive localized heat on the polishing pad can cause heat-fractures inside the gemstone.

Conclusion

Remove the stone from the dop stick by placing it in the freezer for ten minutes—the wax will become brittle and pop right off. Clean any remaining wax with rubbing alcohol.

Congratulations! You have transformed rough earth into a gleaming jewel. Cabbing takes patience, a feel for angles, and quite a bit of practice. Keep your first cabochon forever; it is the benchmark by which you will measure all your future lapidary masterpieces!