To be precise, we should call this cuttlebone casting, because no-one wants a live squid-like creature in the workshop. Cuttlebones are commonly used as a mineral supplement for pets, but they’ve been washing up on the world’s, and Europe’s, shores for far longer than there have even been humans.
There is evidence of their use in casting throughout history, and while I don’t have direct archaeological example to prove it, I strongly suspect that they would have been used by the Vikings and others in the middle ages. It may be that they were used for more than just casting – I’ve seen vague references to them being ground up and used as a polishing powder, so I’ll definitely explore that at a later date. In any case, cuttlebones are fragile, so they wouldn’t last long in the archaeological record – not after they’d been cut up, carved, burnt and discarded.
There are various articles about cuttlefish casting available, including one on Ganoksin. My main purpose in writing this is to try creating a report with photographs – practice for future experiments which will be more complex than this one. (If anyone knows how to get the text to wrap around the pictures, please let me know, because this page looks messy. And yes, I have told it to do that in the visual editor). A response to this article is available here.
The aim of this experiment is simple – casting of small sterling silver items in a cuttlebone mould.
Stage 1: Select two similarly sized cuttlebones. These are available cheap from most pet shops, just don’t tell them what we use them for! If you’re really short of cash or cuttles, then you can cut one of them into two sections (front and back). However, I’ve found a fairly high failure rate from this, as one side of the cuttlebone has a rigid surface, but the other is very soft – one half of your mould ends up very fragile when you are pushing or carving a form into it. Alternatively, if you have a very large cuttlebone, you can cut it in half.
Stage 2: Cut off the tops of the cuttlebones, leaving a flat surface for the “top” of the mould – where the molten metal is poured it. Scrape/file/saw down the length of the cuttlebone pieces, so that they are flat, and then rub them together until they fit snugly together.
Stage 3: Push 3 or 4 “keys” into one piece of cuttlebone, and then press the other piece over it. These are important for making sure that the two halves of the mould line up. I’m using short lengths of wire, but other, better, options are small ball bearings or L-shaped strips of metal. For ease of handling, you can glue the keys into one piece of cuttlebone. Separate the two pieces.
Stage 4: Choose or make a pattern. In this case, I’m just using a hard wax heart. This is carefully pressed into the thickest piece of cuttlebone – at least halfway in, or as much as two thirds in, depending on the shape. In this case, the shape must be exactly halfway because of it’s curves. The second cuttlebone is pushed onto it, taking care that they keys line up. When the two halves are fitting snugly, carefully separate the two pieces, and remove the pattern. If a thick object is being pushed into the cuttlebone, some carving may be required. Alternatively, you can carve a pattern completely by hand.
Stage 5: If your pattern doesn’t have an integral sprue, you’ll need to cut a channel in each side of the mould. This channel should get wider and deeper as it approaches the “top” surface. When the two halves are together, there should be a nice round hole to pour the molten metal into. Finally, cut a number of much smaller channels radiating out from the pattern to the edges of the mold – this is to allow gases to escape the mould when you pour the metal in. Place the two halves together and bind them. I’m using elastic bands, but you could use clamps, tape or similar. The mould should be securely propped up, with the “top” at the…eh…top.
Stage 6: Prepare your metal. I’m using sterling silver, but this will work for various other metals. I’ve done it with gold many times, but platinum is too hot. Work out how much silver you think you need for the item, then double or triple it – the more silver you use, the faster the molten metal will be forced into the mould. As you can’t heat up a cuttlebone mould, this is critical – if the metal cools and hardens, the casting might fail. If you know the mass and density of your pattern, you can work it out very precisely by comparing it to that of silver.
Stage 7: Wearing goggles, heat up the silver in a crucible until it melts – avoid using a flux if you can. After the metal has melted, let the metal cool a little before you pour it in. I know this seems to contradict the advice in stage 6, but if the metal is too “lively” it doesn’t seem to cast as well. Learning how to strike the perfect balance takes time, and I’m not sure that I’ve mastered it yet. Carefully pour the silver into the mould, and let it cool.
Stage 8: Discard the cuttlebones – you’ll see that they contain lots of grey ash, and are no use for further casting. The casting shouldn’t need to be pickled – the photo is straight out of the mold.
Summary: This technique is rarely used nowadays, because the results aren’t amazing, and it can be a very temperamental material to work in. No matter how well the mould is carved, or how clean your impression is, the laminated texture of the cuttlebone comes through as the metal cools, which means that you either plan for an item of jewellery with a stepped effect, or you produce a product which you then forge – for example, you could produce a ring, and them hammer it to a nice shape and surface texture. For early jewellers, this last example is very important – it makes it possible to produce a ring without and hot or cold joining required.
In the cast of my casting, a couple of minutes of filing reveals a more obvious heart shape, but I struggle to see how this method would have yielded attractive jewellery without the use of modern tools and polishing techniques.
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