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How to do cuttlebone casting

One of the oldest forms of casting is a safe and easy source for jewelry-making creativity
Cuttlebone casting
Cuttlebone casting plays a starring role in this dramatic neckpiece that combines forged elements, bezel-set gemstones, and pearls.
Cuttlebone casting Step 1
PHOTO A
Cuttlebone casting Step 2
PHOTO B
Cuttlebone casting Step 3
PHOTO C
Cuttlebone casting Step 4
PHOTO D
Cuttlebone casting Step 5
PHOTO E
Cuttlebone casting Step 6
PHOTO F
Cuttlebone casting Step 7
PHOTO G
Cuttlebone casting Step 8
PHOTO H
Cuttlebone casting Step 9
PHOTO I
Cuttlebone casting Step 10
PHOTO J
Cuttlebone casting Step 11
PHOTO K
Cuttlebone casting Step 12
PHOTO L

Cuttlefish bone or cuttlebone is the center bone of a squidlike mollusk. You’ve probably seen cuttlebones at your local pet store hanging in birdcages for the birds to sharpen their beaks. The chalklike material (calcium carbonate) has a thin, hard surface on one side and a soft crust on the other, making it ideal for direct casting, one of the earliest known casting processes. In direct casting, molten metal directly fills a design carved into a mold surface, producing a mirror image of the design in the finished cast object. Cuttlebone casting is safe, fast, versatile, and inexpensive. It can easily be done with basic jewelry tools and a torch. 

The fragile cuttlebone must be handled with care to avoid cracking the bone. The length and thickness of the bone will limit the size of your casting. Most bones are oblong and range from four to 14 inches (10.2–35.6cm) in length.

Despite its fragility and size restrictions, cuttlebone has its benefits. The cuttlebone mold burns during casting, producing carbon, which keeps the molten metal clean of oxides. It is also easy to carve; any sharp tool will work. Also, due to its organic origin, cuttlebone has growth rings, like wood grain. This distinctive “fingerprint” texture makes cuttlebone a favorite for many artists to use with direct casting. 

Prepare the cuttlebone. Use a spiral blade in a jeweler’s saw to remove the pointy ends of the bone, and cut the bone in half as shown (PHOTO A). Use wire cutters or a small belt sander to shape and trim the sharp outside edge (PHOTO B). 
 
Use 220-grit sandpaper taped to a flat surface to sand the soft side of each half (PHOTO C). Use a circular or figure 8 motion when sanding, putting even pressure on the back of the bone to avoid dishing or bowing the soft surface. This will create a large, smooth area for carving. Do not sand all the way down to the hard shell edges. 
 
Place the two soft sides together and rub them against each other to eliminate any slightly uneven surfaces. If properly prepared, the two pieces should be flush. 

Draw the border and sprue gate. When the two halves of bone are put together, they create the mold. This will be a one-sided mold, so use one half for applying your design. With a soft-lead pencil, draw a border 1⁄4 –3⁄8-in. (6.5–9.5mm) in from the edge (PHOTO D). Your design must fit within this border to prevent the metal from burning through the sides. Do not press too hard with the pencil, as it can actually leave an impression that will cast. Draw a wedge1⁄2–3⁄4-in. (13–19mm) wide in the center of the widest end of both halves. This wedge, when carved out, is called a “sprue gate.” It acts as a funnel for the molten metal, so draw it large. 
 
Apply a design. Use a soft, broad paintbrush to lift away any remaining dust and expose the intricate texture of each half of the cuttlebone (PHOTO E).  Starting at the sprue gate, gently draw your design on the soft surface with a soft lead pencil. Stay within the borders, and remember that the finished cast object will be a reversed image. Also, simple design shapes allow the cuttlebone texture to show, making your finished cast object more interesting.

Carve the mold. Use any sharp tool to carve the sprue gate into both halves of the bone, gently removing the soft surface. The deeper you carve, the thicker the finished cast object will be. Carve a channel between the sprue gate and your design (PHOTO F). Objects can be pressed into the cuttlebone surface to create shapes (PHOTO G). Do not press into the cuttlebone too forcefully, though, as it can break. 
 
The mold will need vents to allow air movement during casting. Carve a few air vents at an upward angle from the edges of your design (PHOTO H). Do not carve the vents completely out the sides or the top. Use soft, nonstick clay to check your design as you work.

Prepare the cuttlebone mold for casting. To reproduce the details of your design, the mold should be clean and free from dust. Use a soft paintbrush to clean away excess material; this will also expose more of the cuttlebone texture. Make a visual estimation of how much metal is needed to fill the mold. Bind the two halves of the mold with binding wire (PHOTO I). Set the bound mold in a pumice pan with the sprue gate up. The mold should be steady so that it will not tip over. Place a crucible, the mold, and the pumice pan on a fire-resistant surface in a well-ventilated soldering station. 

Cast the metal into the cuttlebone mold. Casting is a good way to use up your sterling silver scrap, but fresh casting shot can also be used. Place your metal in a handheld, ceramic crucible. Ignite your torch, and focus the flame on the metal in the crucible (PHOTO J). As the metal starts to melt, add a pinch of powdered borax flux, and stir with a carbon stirring rod. The borax flux and carbon stirring rod keep the melting metal free from oxides. 
 
The metal will puddle when it has completely melted. Pour the molten metal directly into the mold’s sprue gate. Keep the torch flame focused on the metal in the crucible as you pour to keep the metal from freezing (solidifying) before it enters the mold. Fill the mold until the sprue gate is full and no more metal can flow down into the mold (PHOTO K). Set down the crucible and turn off the torch. 
 
The cast metal that has filled the sprue gate is called a “sprue button.” When the sprue button is completely black, the mold is ready to be opened. Use wire cutters to cut the binding wire. Be careful when opening your cuttlebone mold, as the sterling silver casting can still be 400–800°F (204–427°C). Remove the casting from the mold with tweezers (PHOTO L), and quench it in water. 

Clean up the casting. Use copper tongs to put the casting in warm pickle to remove any remaining oxides. Rinse off the pickle in water, and clean the casting with a brass brush and soapy water. Saw off the sprue button with a 2/0 blade in a jeweler’s saw frame, and save the button for future castings.

 

CURIOUS CUTTLEBONE FACTS

  • Cuttlebone was used in the jewelry industry by large-scale manufacturers until the mid-50s.
  • Ground cuttlebone is a fine abrasive used to sharpen medical tools. 
  • At sushi bars, cuttlefish meat is a delicacy.
  • Cuttlefish also produce a brown ink commonly known as “sepia.”  

SAFETY FIRST

Cuttlebone is a very safe, nontoxic mold material. Cuttlebone dust, however, is a very fine abrasive that can irritate the sinuses. Wear a dust mask when preparing a cuttlebone for use. Don’t blow the dust into the air as you sand or carve; instead, use a soft paintbrush to gently brush the loose material out of the way. When finished, use damp paper towels to clean up any dust residue. 

Safety warning: Protect your vision! Wear safety glasses during all metalsmithing procedures.

 

 

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