Introduction: How to Cast and Polish a Pewter Signet Ring
Hopefully this will help a few different groups of people: those of you who want to make a cool ring (and I mean that literally when you put it on in the winter), those of you trying to cast small objects in pewter and don't necessarily need an electric melting pot, and those of you who, like me, just like reading about this stuff. If I missed people feel free to correct me :)
Anywho, let's get started!
First of all, you will need:
- Safety glasses!
- A mold of whatever you're trying to cast. I prefer to use a high temp silicone rubber but you can use pretty much anything that will withstand about 600°F. A good starter project could be a design carved into a cured piece of plaster.
- Some pewter
- A blowtorch or some other method of melting the pewter
- A crucible to melt the pewter in (a steel can will work just fine on a single use basis)
- A hacksaw
- Sandpaper and/or files
- Buffing wheels and compound
- A fair amount of elbow grease, but it's not too much, and it's definitely worth it.
DISCLAIMER & WARNING: Any techniques used here are my own, and they work for me. Use at your own risk. Also, please note that this 'ible details the use of an open flame and very hot molten metal. Please ensure that no pets or small children are around to distract you or get themselves hurt. Nothing is more important than safety, so always work in a well ventilated area (outside is preferable) and it's best to have a friend close by with a fire extinguisher or bucket of water in case something goes really wrong. After the metal has solidified, it is STILL HOT. Use a pair of pliers to handle it or just wait for it to cool down before handling. Same goes for the crucible. If you choose to follow these instructions, have fun, but be safe. :)
Step 1: Prepping the Mold
This is a fairly simple step, but the main point I need to get across here is that you want to make sure you have some kind of lubricant in your mold. In this case I'm using graphite powder (take a pencil and use a knife to scrape the lead so that you end up with a small pile of fine black powder), and I don't really have suggestions for anything else that'd work, so I'd say go with graphite powder (it's easy enough to make, anyway). If you skip this step, you may end up with castings that look like they've come from a golf ball factory.
Basically, take a brush and make sure all surfaces that the metal will touch are coated in powder. That's it! Now reassemble the mold halves and put a rubber band or two around 'em to make sure they don't fall apart when casting.
Now for the fun part!
Step 2: Casting!
It's actually not nearly as hard as it sounds. The concept is simple: melt some metal, pour it into a mold, and let it solidify in the shape of it's container. Easy, right?
Now for the specifics.
I bought my pewter a couple years ago from Rotometals. It's LEAD FREE because this will be a ring, and it's generally a terrible idea to have something that's meant to be worn on a finger (i.e. in constant contact with skin) be an alloy containing toxic lead. The blowtorch can be found at pretty much any hardware store, as can the fireproof surface I'm using (a piece of wonderboard). As for the crucible, I'm using a ceramic dish I got from a jewelry supplier but a clean, dry soup can will work as well for one or two uses.
WARNING: Work outside, wear safety goggles, long sleeves, long pants, closed toed shoes, etc. Use any and all precautions possible to prevent you from hurting yourself or others around you. Always make sure your molds are COMPLETELY dry. If they aren't, the water will turn to steam instantly and shoot molten metal everywhere, including you.
If you got your pewter in ingot form, you're going to want to melt off a bit of it into the crucible so you don't have to remelt the entire ingot every time you want to cast a small piece (if you're using pewter shot, skip this step). I used a pair of long-handled pliers to hold the ingot while melting it, but feel free to do whatever works for you, as long as it's safe. When doing this, try to concentrate the heat of the torch on the bottom corner of the ingot. After you think you have enough metal to get a good cast, put down the ingot and pliers, and place the flame on the metal in your crucible.
Swirl the pewter around a bit while keeping the flame on it to ensure that the entire mass is molten. Now, carefully position your crucible over the mouth of the mold, steady your nerves (take a breath, recite a haiku, think about how you're gonna get to set up the giant inflatable snowman later), and pour in one smooth, consistent motion. Depending on the complexity of the mold and the thickness of the part, you may want to tap on the side of the mold a few times to dislodge any stubborn air bubbles, but experiment*. The lovely thing about metal is that it is infinitely recyclable, so if you get an air bubble you can easily melt it down and try again!
All that's left to do is pull off the rubber bands, open the mold, and pull out your casting! Now ain't that shiny... but not shiny enough. On to grinding and polishing!
*If you still have defects in your castings despite lubricating the mold with graphite and tapping on the side a few times, take note of where the bubbles are occurring. Then simply cut a few vents from there. They don't necessarily need to be too wide or deep, but again, play around with it. I kept getting little v-shaped defects near the base of the ring, close to the sprue, so that's why you see those air vents on pictures of my mold.
Step 3: Grinding and Sanding
These last two steps are the most time consuming step of the process, so be ready for 'em.
First, cut off the extra bits (in my case the metal that filled the sprue and air vents) with a hacksaw, wire cutters, or what have you. From this point, your two main options are filing and sanding. I happen to have a lathe and a sanding pad so I used that, but you could just as easily use a file to quickly bring down those bits.
Now comes the... "fun" part. Depending on how coarse your files were, start with an appropriate grit of sandpaper. I like to start with either 220 or 320 grit, then 320 (if you started with 220), 400, 600, and a final burnish with steel wool. This will leave you with a soft brushed look, which is quite nice in my opinion. But I still prefer a mirror polish, and I'm sure many of you do too.
Step 4: Polishing
To achieve a mirror finish, you will need two different buffing wheels (one for each compound). One will use white diamond compound and the other will use jeweler's rouge. The white diamond has a very fine abrasive called tripoli, which acts like very, very fine sandpaper. It will definitely make your part shinier, but it will still be a little cloudy. The jeweler's rouge then comes in and brings the metal to a brilliant glossy shine.
Congratulations, you're done! Now it's time to either marvel at your creation or give it to a friend :)
Hope you enjoyed it, and feel free to ask about anything I didn't explain clearly enough. Thanks for reading!