Inspired by a video I saw over on Atomic Shrimp, I wanted to have a go at some simple metal casting.
No doubt one of the easiest ways to do this is by using the lost wax method: a process that involves making a wax model of the desired object, encasing it in a material such as clay, plaster, or silicone, and then melting out the wax to leave a hollow shape into which the metal - usually pewter - can be poured.
Making the model
Naturally, consuming a lot of cheese is the first step in this process. Not only does this put you in a good mood for the long, tedious process of forming your model, it provides the perfect material to work with.
I found it useful to allow the wax to cool for a while in the fridge if it was getting too soft from the heat of my hands, and to use toothpicks to help with some of the fine details.
An unhealthy amount of Babybels later, I was able to make this little model rabbit.
The cone shape at the bottom is called as a sprue. This is necessary to produce a channel in the mould through which to pour in the metal (remember the cavity will be a negative of this shape), and also acts as a reservoir of extra metal while the casting cools and potentially contracts.
Mixing the mould
For the mould itself I used a high-temperature two-part silicone that's designed for use with metal casting. Although a bit pricey compared to plaster or clay, it sets much faster and can be reused multiple times. As I don't have a vacuum chamber, I had to take extra care when mixing to introduce as little bubbles as possible.
I found a suitable container to pour this into (the sacrifices I have to make for this project), taking care to avoid introducing air bubbles by pouring slowly in a single stream into a corner, rather than directly over the wax model inside.
By the morning the silicone had fully cured and I could start removing the wax. Traditionally this would be melted out in a low-temperature oven, but instead I cut the mould open in a zig-zag pattern and removed it by hand. Because the silicone is semi-flexible, the two parts fitted back together easily afterwards. It also meant I wouldn’t need to cut the mould open again later to remove the finished casting and risk scratching it in the process.
Casting
With the wax removed and the mould firmly taped back together, I broke out my portable gas stove and melted down a cheap pewter tankard I found in a charity shop.
Modern pewter is an alloy made of tin and small amounts of antimony and copper, but it's worth being cautious with older, unmarked pieces as they may contain lead. I did this outside and in a saucepan I don't use for anything else.
Pewter is often used for metal casting because of its low melting point (around 170–230°C), so melting this tankard didn't take long at all.
I quickly poured this into the mould and allowed it to cool. It was fairly well behaved, there was no bubbling or spitting, and I had plenty left over for future casts.
Within a few moments the pewter had set solid, and after dousing with cold water it was cool enough to take apart the mould and tidy up the cast.
Not bad! I cut off the sprue with a small hacksaw and glued on a small dark-purple rhinestone for each eye. It's far from perfect - the body is very rough (probably on account of bubbles in the mould) and it's missing a leg, but in a way I think this just adds to its charm.
Conclusions
I think if I were to do this again I would cast something slightly larger; making such a small model was very finicky and the pewter was too viscous to reach into the extremities of its thin legs. Perhaps adding some venting holes or pouring channels would have helped with this.
Although the silicone I used was advertised as not requiring a vacuum chamber, having one would have been very beneficial. No matter how carefully you mix the two parts together, you're bound to introduce pockets of air into the mould and cause an uneven appearance on the finished piece.
I also had a small amount of silicone leftover, which I left to set in a glass as a practical joke.
Rather effective I think!