Carve a custom stone with your Flex Shaft, Part 2

Get some diamond bits, get a plan, and get started. 
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To the uninitiated, the phrase “gem carving” could sound intimidating. But it’s not impossibly difficult or scary. If you have a plan mapped out, all you have to do is remove a little bit of stone at a time until your design is revealed. Simple, right? In fact, the trickiest part is not removing too much gem material at once. It’s easy enough, if you go slowly and think out each step as you work.

To make this project even better, the only major tool you’ll need is your flex shaft, equipped with some diamond-coated burs and sanding disks. Sure, you can cut your own stone with a lapidary trim saw and then grind that stone with a lapidary grinding machine. But if you don’t have those pieces of equipment, you can begin carving a cut piece of stone called a “preform,” or you could even carve a finished cabochon. Either way, the carving procedure is the same.

Follow these instructions to carve, refine, finish and polish your stone. Need help getting started? Check out Carve a custom stone with your Flex Shaft, part 1 to learn how to select your stone, prepare it for carving, transfer your design and start the carving process. 


  • A stone to carve, such as Andamooka rainbow matrix opal (choose from):
    • Rough gem material
    • Preform stone
    • Cabochon
  • Dust mask
  • Lapidary equipment (optional):
    • Trim saw
    • Flat lap machine, 400-grit diamond flat lap
  • Shape template (optional)
  • Water drip system (optional)
  • Flex shaft and/or handheld rotary tool
  • Diamond burs: various shapes and sizes
  • Wet/dry sandpaper and/or sanding disks: 200, 600, 900, 1200 grits
  • Magnifier
  • Clear lapidary sealant, such as Opticon



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At this point, you should have chosen your stone, shaped it into a preform, and refined the base. Your design should be transferred to the stone and basic carving should be in place: low points, basic planes and mid-depth points. Now you're ready to take these steps:

Define the base. Carve the flat base of the stone, loosely defining an even top edge. To define the top edge of the base at the back, under the abdomen, I had to carefully carve an undercut that curved from the bottom of the abdomen to the top of the base [PHOTO 10]. 

Switching to a smaller diamond bit if necessary, further define the shapes in your design and the top edge of the base.

Define the outer edges and details. Working slowly and carefully, define the more delicate details, such as the outer edges [PHOTO 11]. The outer edges of my stone include the spider’s legs; the subtle angles of these legs require additional attention. 

Keep in mind that you can use the textured side [PHOTO 12], end, or edge of the diamond bits to make your desired cuts. Visualize the planes of each segment of your design and the lines that you’ll need to connect those planes. It may be helpful to draw guiding marks on your stone to keep yourself oriented as you carve. 

Remove a small amount of material at a time; you can always carve more later. 

Refine and deepen the design. Using the shaped diamond bits best suited to your design, deepen the grooves and refine the shapes [PHOTO 13]. 

Make sure your base remains an even thickness all the way around; each part of the design needs to gently slope or curve to the top edge of the base. Redraw guide-lines if necessary. 

If you use a long thin diamond bit, use the side of the bit and avoid directly carving with the point. Using the point will quickly make little holes in your stone and can create more cleanup work later. 

Make sure to keep small detailed parts, such as the legs on my stone, about the same thickness [PHOTO 14]. This will help prevent them from cracking or breaking off. In my piece, I chose not to fully separate the legs. Instead I created enough definition with grooves to suggest the look of separation while still maintaining a solid, stable stone.

Create any undercuts, if necessary. To decrease the chances of breaking your stone, don’t carve too deeply into the sides or under the design of the stone until your design is fully finished on top. 

Using a ball-shaped diamond bit, gently begin to remove material from the sides of your stone [PHOTO 15] to create any undercuts in the design. On my piece, I also removed material from under the spider’s legs on the top of the stone [PHOTO 16]. If you remove too much material, you could compromise the stability of the piece. 

Contour the top of the base. Remove just enough stone from above the top of the base to tidy up any irregularities and make it an even thickness.

If you plan to prong-set your stone, you’ll need to make at least two small indentations along the top and sides of the base [PHOTO 17], forming a slight hourglass shape. These indents will give the prongs a place to grip and prevent the stone from shifting in the setting. 

If you plan to bezel-set your stone, carve so that the base tapers slightly — wider at the bottom, narrower at the top. This will help the bezel wire more firmly grip the stone. 
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  • Choosing the best burs for your design will make the carving process much simpler and can prevent overcutting and unnecessary cleanup. I use a selection of burs to suit my carving needs. 
  • Select the shape of the bur to fit each part of your design; i.e., rounded areas, crevices, the flat plane of the base, details, etc.
  • Each bit can either make an impression of itself in the stone when you hold the bit in place, or the bit can make a trail when you pull it across the stone. So when you need to choose a bit, don’t just look at its shape, also visualize its trail.
  • Most of the time, keep the bit moving with a light, flowing touch.
  • Keep water dripping over your stone, or dip your stone in water frequently to keep the stone cool, to prevent dust, and to prolong the life of your burs.
  • I like to use both my flex shaft and my Dremel rotary tool as I work. I keep different burs in each tool so that I can quickly use one to re-mark a reference point, and I don’t have to change burs for little touch-ups.
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Diamond bits fit in most standard flex shaft handpieces and are available in many shapes and sizes. For optimal results, choose the bit best suited to each part of your carving.
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Smooth the design. You need to smooth any carving marks left on the stone prior to sanding and polishing. To do this, use larger rounded and cylindrical diamond burs to go over the stone lightly [PHOTO 18]. Don’t remove too much material.

Use a small ball-shaped diamond bur for areas where larger burs won’t fit, but keep your touch light and the bur moving. Inspect the stone carefully, and smooth any areas that still need it. 

Sand the stone. Using 200-grit sandpaper or a 200-grit flexible wet sanding disk attachment with your flex shaft, sand all surfaces of the stone. Use the edges of the sanding disks [PHOTO 19] to reach into all the narrow grooves that would be difficult to hand-sand. Incorporate a continuous rocking motion with the disk to avoid forming flat spots on your stone.

After you’ve sanded every part of the stone with 200-grit paper, thoroughly rinse the stone with water. Then progress to 600, 900, and 1200 grits. Before you proceed to each new grit, use a magnifier, such as an Optivisor, to check that you’ve removed all marks from the previous grit. 

NOTE: If you’re using Andamooka rainbow matrix opal, you will continue to see a slightly grainy surface, even after creating a smooth, well-sanded finish. 

Apply sealant. Due to its porosity, Andamooka rainbow matrix opal doesn’t take a traditional polish well. Sanding will achieve a good pre-polished state [PHOTO 20], but to achieve a shiny, polished surface, you will need to use a clear sealant, such as Opticon. This type of sealant also does a wonderful job of bringing out the natural color and fire within this opal type.

Dry your stone completely. Following the manufacturer’s instructions, carefully apply one very thin layer of sealant to achieve a natural look. You can also selectively apply the sealant to enhance contrast, like I did by applying it to the spider and not to the base [PHOTO 21].

To learn a great setting for this custom spider stone, check out this project: Two-prong settings for irregular stones 


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