Intro: Casting Pewter in Soapstone
Some little time ago, I decided that I would learn more about making items out of cast metal. I did some research to find a metal that was relatively easy to obtain, had a low melt point and would be reasonably attractive (bright and shiny). I also researched different methods of casting.
What I came up with was using Pewter. Pewter is a mixture of tin (85 - 99%) with Copper, Antimony, Bismuth. Older types of Pewter contain lead and some contain silver. Copper and Antimony are hardeners in the pewter.
I found that I could go to lots of recycling places and buy pewter tankards and other vessels for a pretty low price ($1 - $8) so a supply wasn't going to be too difficult, although the price of these items seems to have come up in price over the last couple of years.
Soapstone is a very soft but stratigraphically stable kind of stone. It's made from old crustaceans that have been crushed under thousands of tonnes of sediment over many thousands of years. Crushed soapstone is the main ingredient in talcum powder. It's mineralogical name is Steatite. I bought an 15 x 15 cm block of soapstone from an art supply store for $15.
The great thing about soapstone is that it can be worked very easily with woodworking tools and is generally pretty clean and safe.
Okay, pewter has a low melt-point around 230 degrees centigrade. so it's also pretty easy to get it flowing.
If you are interested in doing some pewter casting, you are going to need a few things:
- some old pewter objects (tankards, etc. from a second hand or recycling shop) Start with just one object.
- some craft carving knives
- a hand saw
- some metal clips
- a source of heat (I use a butane camp oven)
- an old metal ladle (don't use aluminium)
- an old saucepan (don't use aluminum)
- a baking tray
- a muffin tray (for making ingots)
- fine files
- fine sandpaper
Step 1: Let's Get Started
The first thing that I did when I got the soapstone home was to square off the sides. I did this using a bandsaw, but I could have done just as easily using a hand saw.
The saw leaves some rough edges on the material, but that is easily sanded back with some medium grit sandpaper.
Then cut the soapstone into 10 - 15mm thick pieces. You really only need to smooth one surface down, that is, the inside surface of what will be your mold.
A little preparation here will save you time later on, the smoother that you can get your inner surface means that there will be less flash on your cast piece, which means less cleaning up of the metal later on.
When I've smoothed the inner surface well with a fine grit paper, I then wet the surface and rub it on cotton drill fabric, this brings the surface to a very nice polish.
Step 2: Transfer the Design
To make my life easier, I pair the two sides of the mold and cut or draw registers across the joint so that I can easily locate and orient the pieces for designs that are on both faces of the soapstone and to make pouring easier.
You can draw straight onto the surface using a soft lead pencil. The thing to remember is that it is a mirror reverse of what the finished product will be.
Carving the design using craft knives and files can be tricky, the soapstone is quite a soft stone, but it is still stone and will crack if you are not careful.
I found it easiest to carve in planes, that is carving down to the same (about 2mm) depth for the body, before I started working on the detail.
Slow even strokes and cleaning off the dust often makes the process reasonably easy. If you have a rotary tool (such as a Dremmel) you can use that, although it throws dust everywhere!
Occasionally, I clean the carving with running water and my fingers. I have also cleaned the surface with a toothbrush, but, be careful, too much pressure on the toothbrush will erode your carving.
When you are carving your design, make sure that you avoid undercutting edges, this will make it difficult to remove the metal piece and you will almost certainly damage the mold.
If your design is 2 sided, a trick that I came up with while experimenting is to carve half of your design (with a gate) and pour the molten pewter into the mold. The cast side of the mold gives you something that you can trace around to give you the back side of the design. Just let the metal cool, open the mold, leaving the pewter in place and trace with a pencil or a sharp knife to etch the border.
Step 3: Gates and Sprues
You want to carve some gates (holes that allow you to pour the molten metal into the mold) and sprues (channels in the mold that allows metal to flow in and air to escape.
I usually make my gates a funnel shape so that it is easy to pour the molten metal into the mold without it pouring everywhere.
For gates, you want to make sure that the metal can easily flow into all parts of the mold at more or less the same time, you don't want the metal to cool too much before it gets into the extremities of the mold. Where you have narrow points or bottlenecks in your mold, try to accommodate for this by carving extra channels for the metal to enter.
If you are casting something that has a large void in it, add another gate for metal to escape the mold when it is full, as the metal cools, it will contract, so a reservoir will draw still hot metal into the void from the sprues and gates.
An extra gate also helps you to gauge when the mold is full.
When the casting is cool, you can cut the gates and sprues away with a metal saw, files, dremmel, chisel, whatever (so long as you are careful!)
Step 4: Heat the Metal
Heating pewter is not a very difficult process, but be careful not to burn it. If you let your metal get too hot, it will start to colour (yellow, brown, purple, some other colours ... but I'm colour-blind).
While your metal is heating, match the two sides of your mold together (using your register cuts or marks) so that they are oriented correctly.
I have some spring clamps from leatherworking/woodworking that I use, these are not a very strong clamp, and you don't want to exert too much pressure. It would be sad to break your mold after all of that etching and polishing.
Make sure that you set your mold down on a heat-resistant surface. I use a piece of old cement sheet and a baking tray under my mold in case I get spill. Better not to burn down the workshop ;)
Either pouring directly from the pan or by using a metal ladle, pour the molten metal into the mold. As the mold fills the mold will get hot. I found it uncomfortable ... and I'm used to handling hot food.
Step 5: Clean Up
When the metal is cool enough to handle, you can de-mold it. Leave it in the mold as long as possible so that the metal has a chance to shrink properly.
Usually, there will be some flashing, that is, metal that has seeped out of the void and between the two halves of the mold. This can be cut away with a sharp knife, a file, a dremmel or a chisel. Exercise care here, the pewter is hardened and may not be very easy to cut. A dremmel and files are the tools that I use for this process. I used to use a sharp knife and files, but cut my fingers more often than not ... so the dremmel became my go-to tool.
The above images show some of my earlier work with pewter. I made a badge for some friends, a nubian goat pendant and a bunch of buttons.
Since then, I've made several other bits and pieces including some reproduction coins and more badges for medieval re-enactment folk and some fancy pants aglets.
The great thing about casting pewter is that you can recycle the main material over and over, so you can continue to improve your methods and skill without having to continually replenish your supplies. Of course, the steatite isn't that recylable ....