Cuttlefish Casting

by Jamie Hall on February 22, 2010

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.

 

A Cuttlebone, soft side up

Stage 1: A Cuttlebone, soft side up

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.

Two cuttlebone halves

Stage 2: Two cuttlebone halves

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.

Cuttlebone with "keys" inserted

Stage 3: Cuttlebone with "keys"

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.

Cuttlebone with pattern and sprue

Stages 4 & 5: Cuttlebone with pattern and sprue

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.

Cuttlebone with radial grooves for escaping gas

Stage 5: Cuttlebone with radial grooves for escaping gas

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.

Completed mould, viewed from the top

Stage 5: Completed mould, viewed from the 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.

Burnt-mould from a different casting

Stage 7: Burnt mould from a different casting job

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.

The casting, with sprue

Stage 8: The casting, with sprue

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.

Casting and original form

Summary: Casting and original form

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.

Jamie Hall
Contempory and Medieval Metalworker
Jamie Hall

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{ 8 comments… read them below or add one }

Lois Martens February 27, 2010 at 11:23

You rattled my cage. But I have so much to say about cuttlefish bone casting that it wouldn’t fit in a comment so I will publish a counter blog. I’ll let you know here when it is online. Lois

loiskmartens February 28, 2010 at 16:29

I have posted to my blog on Ganoksin. It’s title is “Counter Blog to Jamie Hall’s Cuttlefish Casting Blog”. My blog is called Jewelry by Lois. All the best, Lois

Jamie Hall February 28, 2010 at 23:48

I’ve put a link to your blog post in the article above. Is there anything else I missed or could try in the future – I saw the suggestion about using a strip of zinc – doesn’t that cause the fineness of the alloy to drop?

I did some checking, and it seems that Italy doesn’t have a standardized hallmarking system – I’m worried that even if I accounted for adding zinc when I produced an alloy, I would still fail assay if the zinc wasn’t spread uniformly.

Michael Johnson March 17, 2011 at 21:46

Great post! I actually plan to put up some videos on cuttlebone casting in the near future. To make your text wrap around your photos is to make it justified in xhtml. But it this might depend on the content management software you use. If your using wordpress edit the photo and you click the icon with all the text around the photo.

BlueCrabBay March 22, 2012 at 00:15

Wow! This post is a disservice to all inspiring jewelers, way to discourage!

george holloway March 31, 2012 at 22:32

HI,
SURPRISED “YOU FAIL TO SEE” HOW VIKING AND EARLY CRAFTSMEN COULD ACHIEVE A FINISH WITHOUT MODERN TOOLS ETC.HAVE YOU NOT SEEN GREEK,EGYPTIAN,BRONZE AGE,& ANGLO SAXON WORKMANSHIP?
THEY CERTAINLY DID NOT HAVE MOTORISED TOOLS,FLEX SHAFTS,ETC.

Jamie Hall March 31, 2012 at 22:53

I’m not sure that I follow. Cuttlebone casting is not without it’s uses, but it’s hardly the preferred method for most situations. There were a wealth of other ways to cast, and the high quality of many ancient castings suggests that a lot of though was put into which method to use. In Herbert Maryon’s “Metalwork and Enamelling”, he mentions a method of saturating the surface of the cuttlebone, to improve the finish that it leaves, and that’s worth trying for the future. Otherwise, I find that cuttlebone leaves such a deep pattern of ridges that large amounts of metal are wasted, and any detail on the original model will be obliterated by the attempt to clean up the surface.

It could be the you have misunderstood the point I was making – I’m not talking about the capacity of ancient metalworkers to create nice surface finishes, rather I’m saying that cuttlebone isn’t a brilliant route to achieving a nice surface finish.

It might be a more enjoyable conversation if you turn capslock off.

stewart August 25, 2012 at 10:50

Hi
have a look at my youtube video === cuttlefish casting a roman style bronze seal ring,
this will show you just what interesting peices can be made with this method of casting.

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