Tuesday, 18 January 2011

Casting silver in cuttlefish bone

I have been wracking my brain and trying various things to recycle my scrap silver. Ideally I would simply cast into an ingot mould then use a rolling mill to produce sheet or wire. Unfortunately I am unable to obtain a rolling mill here in France and the cost of transporting such a heavy item from the UK is prohibitive.

I first tried casting into beach sand, which was ok if you wanted an amorphous textured lump. I tried melting the scraps into large lumps and then hammering them out to get a useable thickness, this too was fine if a little labour intensive.

Here is a picture of two pieces of hand hammered scrap, one gold one silver. The silver I managed to get down to 1.35mm and the gold down to 2.22mm. The silver is 3.5cm in diameter and the gold 2.5cm in diameter.  Both of these took some considerable time of bashing to get to this state, annealing frequently, after which I had had enough.

Then I chanced upon cuttlefish bone casting: well this after two attempts has proved to be not only the most fun, but also a very effective way of using my scrap. So I thought I would write up my progress and the way it is done, not so much a tutorial as I am still learning but to show the principals and how easy it is to get started.

The image to the left is the first try, using a seashell. An encouraging first attempt. It lacks definiton of the texture of the shell and is a little on the short side. I have since worked out the possible reasons for both of these problems.

The funnel I cut in the shell did not have a sufficiently large enough hole to let the molten metal drop through quick enough and so it solidified in the funnel and the problem with the texture is probably due to there not being enough texture on the original.


The image on the right here was a rather more steady and considered approach rather than trying to run before I could walk. I cut a simple square out of the bone, made a wider funnel and poured the metal more steadily and not quite so fast as the first. The reason it is irregular at the top is because I made the mould bigger than the amount of scrap I was using and it was evidently not level in the sand. The texture you can see is the natural texture of the cuttlefish bone which is rather nice.

I am lucky, in that I live close to a beach and I picked up a carrier bag full of cuttle bones the other day. Having done a bit of hunting round on the Internet, I found out the basic idea of using them to cast small one off pieces (or multiples if you use a hard model to impress into more than one bone).  Cuttlefish bones can be bought at pet shops too as they are given to caged birds to do goodness only knows what with, you can even buy them on Amazon, in the pet supply section.

My local beach
You will need the following:
Materials 1

Cuttlefish bone
Hacksaw blade or similar
Sand paper
Craft knife
Matchsticks or cocktail sticks
Wire for binding the two halves
Container filled with sand or earth





Scrap silver
Materials 2
Scorifier dish
Tongs
Torch
Borax
















The method is simple: you take your cuttlefish bone and cut off both ends keeping the widest possible part for your casting.

Bone prep 1

This is now a squared off piece oval shaped round the girth. Cutting the stuff is very easy, I used a cheap hack saw blade with no handle and it goes through with little effort, one side of the cuttle is a little harder but if you tilt the bone you should have no trouble getting through.

This piece is then cut lengthwise to give yourself two flat parts, rub each flat part on sandpaper to smooth them off and you now have the basics.

Bone prep 2
If you are taking an impression of something, select the thickest part and lay your object on the surface of the bone, positioning it nearer to the bottom of the bone, in order to leave yourself room too cut a funnel at the top end into which you will eventually be pouring your molten metal. (note objects with undercuts will not work with this technique) Make your funnel at the wider end, the rays of the texture are cup shaped which will remind you which way is which.

Now push your model into the bone, it is quite soft and should just go in with some squeezing, (I have found a gentle rocking motion is better to ease it in) if it does not, lay a small piece of wood on the object and use a small g clamp to coax it into the bone. Once the object is effectively buried half way into the bone, lay the bone on the table and push four cut matchsticks or cocktail sticks around the impression to help you line up the other half later. You will notice that with solid objects the finish is smooth, you do not get the texture of the cuttlefish bone showing as much as you do with a carved out design.

Take the other half of the bone and lay it on to your object which is still embedded in the bone and squeeze the two halves together gently but firmly until the two halves meet and there is no light showing between them.  As you do this, the cut matchsticks will make their own holes too.

Separate the pieces, remove the object, and then with a needle scratch some venting holes out from the impression to the edge of the bone. At the top of the impression cut a funnel shape to pour the metal into, make it reasonably wide so the metal can fall quickly into the hole. Place the other half of the mould on top using your matchsticks as guides so it meets up properly, then bind the two halves with wire, taking care not to offset the two halves.












Set the mould upright in sand or dirt whatever you have to hand to keep it steady.

You can of course just carve your design directly into the bone with a craft knife, which is what I have done here in the next few photos. It is very easy to work, if you do this just brush out the dust and scraps with a small brush before putting the two halves of the mould together. You will notice too that your design can be lightly drawn in pencil. I used the pin head in the picture to indent the paw pads, the heel part was cut out with the knife as was the square part.

You will see from attempt 1 pictured below, that I did not cut a sufficient funnel to let the metal flow into the mould. If you look at the scorch marks it shows quite clearly the metal arrived at the bottom but then seized up in the funnel. I Just cut another one and tried again in attempt 2 with more success. I made the funnel wider and the vent holes a little deeper, still not perfect but this is still only the fourth cast I have made.

The funnel and vent lines can be seen in the second picture.

Back to work and another go, this time I cut out a simple arrow head shape (see pictures below) and made sure the funnel was wide enough and that the vent holes were indeed venting right out to the very edges. This cast was much more successful. You can see in the photos once it was cast that the metal travelled up the vent holes. This excess metal is easily cut off and saved for your next casting.


Carving the bone 1

Carving the bone 2

Bone wired and sitting in sand ready for the metal






Insufficient funnel attempt 1


After opening attempt 2
Simple arrow carved into bone






Bound with wire


Showing funnel


Just opened


Arrow head cast


Finished

Take your scrap, and melt it in the usual way using borax ( I have no borax powder so I grind up pieces broken off my borax cone, which is what is in the mortar in the photo materials 2) and get it to the point you know it will flow freely, pour it into the mould.

I have melted small amounts of silver like this using the little mini torch, it is obviously quicker with a hotter torch like the oxy/gas one seen in the photo.

 It is done. It will stink to high heaven. Leave it to cool or quench it, undo the wires pull the two halves apart and there you have your new silver piece from scrap. Cut off any excess at the funnel part and file off any extra metal that crept up the venting holes.



The photos will enlarge for better viewing if you click on them.

This post is a work in progress.

9 comments:

  1. Very informative and useful. Thank you for taking the time to put it all together so clearly. I can't wait to try it out myself.

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  2. Thanks for a really understandable tutorial on this type of casting. I never really understood it before, but now am willing to try it!

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  3. Great info Kwant I tried this once, but my pieces were to thick, I probaly made the indention on the cuttlebone to deep anyway I enjoyed the extra info and I will try it again please keep us updated on your cuttlebone castings.

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  4. Thanks for taking the time to make this tutorial and share your experiments with cuttlebone casting. You helped fill in the blanks left after reading a couple of magazine tutorials.

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  5. Good job! See how I do the same technique in my jewelry making blog

    http://metalsmithorfebreria.blogspot.com/2009/08/tecnica-de-fundicion-en-hueso-de-sepia.html

    I do it slightly different :)

    I have being reading couple of your articles very instructive!

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    1. Hi there, I like the way you do it very much, saves on the cuttle bone too. I am guessing the block is some kind of firebrick?

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  6. Hi Kwant

    That is correct is a firebrick these can be found in any hardware store it will save you half of your material. See my new items at : www.metalsmithorfebreria.blogspot.com

    Ciao!

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  7. Hi, great blog. I experimented with cuttlefish for a couple of years using a propane torch before getting MAP gas. I found that heating the cuttlefish in an improvised oven over a small gas burner improved the success rate. To do this we support the cuttlefish in a jam tin and pack pebbles around the cuttlefish then invert a large tin over the cuttlefish to form the stove.

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    Replies
    1. Thank you Gordon for the tip, I will certainly give your suggestion a try.

      Of late I have been using Delft clay as the cuttlefish on our beaches have become a little scarce.

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