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Cuttlefish Bone Casting

November 28, 2011

As said in the previous post, I had two more birthday gift to prepare… well, this is one of them.
Feeling bold, I wanted to try a peculiar technique used since the VI century from jewelers in the mediterranean area to cast small objects: Cuttlefish Bone casting. The cuttlefish bone is soft enough to be carved (or impressed with an existing object) but resilient to heat to receive molten metal.
In the past, I already experimented a bit with this technique, with mixed results.. I wanted to try another time, with a better idea of what I wanted to obtain: in this case, a spiral shell to be used as a necklace.

I started from some cuttlefish bones, got it from the local  supermarket, in the pet department (they are usually given to birds).

To build the mold, you need two sides: if the bone is large enough, it is possible to cut it in half and flatten it with some sandpaper. Since, in my case, all the bones were quite thin, I used two of them, flattening one side of each bone using sandpaper, until the two flattened sides were large enough to accommodate the design, and precise enough to adhere perfectly.

Using a reference image, I traced the spiral on the flattened side of one of the bones, obtaining a good impression of the shell outline.

I later carved the front side of the shell, following the outline. As visible the images below, I tried to obtain a round shape for the spiral body which decrease in depth as we go towards the center of the shell but, at the same time, keeping clearly visible the ridge between the coils.

Using a couple toothpicks I made two pegs to holt the halves of the mold in the proper position. On the other half of the mold, I carved a simple shape, matching silhouette of the front part, to give the piece a bit more thickness. The V-shaped notch in the top part (in green in the image below)  is the channel to pour in the molten metal.

After the carving, using a brush, I carefully cleaned the inside of the mold, bringing out again the grain and veins of the cuttlefish bone: this is really important, since the three-dimensional pattern of the bone will show up on the casted object surface, producing a wonderful organic pattern.

I actually had to carve two casts, since the first one failed (as shown later on).

Then, the casting: I used a gravy ladle as a crucible, and old Warhammer miniatures as the source of metal. Miniatures, especially newer ones are made of a special alloy called “White Metal”. White Metal is non-toxic (miniatures were made of lead alloy, then deemed inappropriate for kids, so this new alloy was introduced), easy to smelt (you can smelt it on a gas stove, possibly using a small butane torch to help keeping it flowing when pouring it), easy to shape using files and can be brought to a nice shiny finish.

Cuttlefish bone can withstand also a cast in silver, but hey… this was a test (and, beside, I have nothing hot enough to smelt silver).

So, I smelted couple of black orcs in the ladle and, keeping the molten metal flowing with the torch, poured into the mold until full. Be sure to close the mold tightly, otherwise the molten metal will exit on the sides, ruining everything, like it happened to me on the first try… the photo below shows the molten metal leaking near the bottom of the mold). In any case, some metal will overflow, so be sure to place the mold in a container with non-flammable material. During casting, the hot metal will make the mold smell like a fire of rotten fish on the seashore… not pleasant at all 😦

After 3-5 minutes, the metal and the mold will be cold enough to touch. Carefully open the mold and take out the piece. The object will have some unwanted surfaces (the metal that slipped between the two halves), and the pouring channel will be solid metal. With a cutter, I removed the large unwanted part and, with files, I fixed the shape on the borders. It is a good idea to wash the piece with a strong detergent, since its surface will be dirty with burned residues.

It is not possible to do a second cast in a used mold: the bone absorbed the heat keeping its shape during the first pouring, but will just crumble if used a second time. This, however, is one of the nice things of this technique… each object is unique.

I finally used some Judaic Bitumen to give depth to the piece by darkening the recess areas and the veins. As usual, the bitumen was applied, dried and then brushed away from the raised areas with very fine abrasive sponge.

The result is visible in the first images of this post: a somehow organic-looking shell. The patterns of the bone have been transferred to the metal surface; this is the distinctive tract of this technique, a wonderful texture especially suited to jewels depicting living objects.

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