In this instructable, we'll be casting old pewter tankards into small jewelry, pendants, coins and whatever else you can think of. I'm using 3d prints to create a negative mold into a heat resistant silicone, but you can cast pretty much any object. I'll be showing how to make basic one sided molds in this tutorial, but more complex double sided molds are possible too.
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Step 1: What We Need.
First off, you'll need something you want to cast in metal. I'm using a wolf head ring I printed in PLA for this tutorial. A 3d printer isn't required though. You can use traditional means to create your object. Use something simple for your first projects. A pendent or coin is a good choice.
Next, you'll need the silicone to cast your metal. While it's possible to use sand or plaster, I find they both have their problems. Plaster contains water and will crack when the water evaporates and sand gives you a very rough surface, and doesn't capture small details. I'll be covering green-sand casting with zinc and copper in a future instructable.
I'm using mold max 60. It's not cheap, but it gives the best possible result. You can buy it from amazon. https://www.amazon.co.uk/Mold-Resistant-Silicone-R... (uk link)
Now you need the metal. I get my pewter from old tankards I buy from charity shops. The old battered ones are best because they are the cheapest. You'll be cutting it up and melting down the metal, so the quality doesn't matter. Don't worry if the metal looks dull, it'll look like new once melted down. You can also buy pewter ingots online.
You'll also need something to melt the pewter. I'm using a furnace, but that isn't necessary. Pewter melts around 170-230 C, so you could use a blow torch or even a stove. If you have a furnace, set it to 240C. Otherwise, heat until the pewter begins to melt, more details on that later.
Step 2: Preparing Our Object.
If you're using a 3d printer, make sure you clean up your print. The silicone will pick up every small detail, even the individual layers. Give it a good filing. A small set of files is perfect for this. Otherwise just use sandpaper.
Once your object is clean and smooth, you'll need something to put it in. Ideally, you want a container that's a little bigger than your object. Anything bigger, and you'll be wasting silicone. You can use cardboard tubes for this. Just hot glue a base onto it. Make sure there's no gaps. It might be worth sticking your object down with glue before you pour the silicone. Especially if you're using a 3d print with low infill. Otherwise your object may float to the top before the silicone had time to set.
Make sure the object is the right way up. The side with all the details should be facing upwards.
Step 3: Making the Molds.
Now it's time to mix the silicone. First estimate the volume needed. You'll want to mix a little more silicone than needed because there'll probably be losses. Find the ratio of silicone to activator. With mold max 60 it's 100 parts A to 3 parts B by weight. You'll need a gram scale for accurate measurements. I got mine for £13 on amazon.
Pour the amount of silicone you need into a pot. I highly advise wearing gloves when doing this. The silicone gets everywhere and is very difficult to get off your hands. Rubbing alcohol is great for removing it from your countertops. Don't pour the silicone into your nice measuring jug though. Instead, measure it with water, then pour the water into a disposable pot and mark how high the water is. Empty the water and fill the silicone to the line you've just drawn.
Now weigh the silicone, remembering to take the weight of the pot away from the final measurement. Now you need to add part B; the activator. The silicone will only set once this is added. Assuming the ratio required is 100:3, take the weight of your silicone and divide it by 33.3.
Let's say you used 150 grams of silicone. You need to add 4.5 grams of activator. Place a second pot on your scales and zero them. Now slowly add the activator (with a pipette if you have one) until the scales read 4.5 grams. Then add the contents to your first pot and still well.
Make sure the mixture is fully mixed, otherwise the silicone won't set properly. Once that is done, it's time to pour.
Now, you're meant to use a vacuum pump to get rid of all the bubbles from your silicone before pouring. I Didn't have one. If you happen to have a degasser, use it. Otherwise do what I did.
Pour the silicone slowly from about waist height, with the container with your object on the floor. (Please cover the floor with newspaper first) This will stretch the silicone as it falls, and get rid of any bubbles. Try to pour in one place at the lowest point of your container.
When you're done, leave the silicone to set. Wait at least 20 minutes before touching it. Then put it somewhere safe, and wait 24 hours for it to set properly.
Step 4: Getting Ready to Cast.
When the molds are set, remove them from your container and carefully remove your object. Single sided molds are easy. Just pull the object out. More complex objects require you to cut the silicone in half to free your object.
If you want to know more about casting complex objects in silicone, there's a great youtube channel called punished props, I recommend checking it out if you want to learn more. They can be found here: https://www.youtube.com/playlist?list=PL6q0fd3ileW...
You can just pour the pewter directly into the mold. This works for some objects like the ring I used for this tutorial, but some objects with flat backs get a much better result if you cut a channel in the top of the mold, clamp a sheet of metal to both sides, and pour into the channel. See photos for details.
Step 5: Casting!
Now comes the fun part. Casting the metal.
Thick gloves and eye protection are a must. You'll be handling liquid metal and things will get hot. A respirator is recommended too. I'm using English pewter which is supposed to have no lead content, but a respirator should be worn when dealing with any metal fumes.
I've added a video of the casting process. It's pretty simple, but takes a bit of practice.
Get the furnace/ blowtorch, stove, whatever else you want to use, heated up, then add the pewter into a heat resistant container. Don't let it get too hot though, or you'll burn the pewter. You're aiming for no higher than 240C.
When the metal has melted, scape off the stuff floating at the top with a metal spoon. This are impurities, called dross or slag. When you see a shiny liquid metal, it's time to pour.
Act fast, but don't rush. Too slow and the metal will set before you've filled the mold, too fast, and you'll spill the metal everywhere.
Once it's cooled down (this happens in minutes with pewter) use pliers to remove the pewter from the mold. Place it in water to make sure it's cool enough to touch.
Don't expect a good result the first time. There's often a little bit of moisture in the mold which causes air bubbles. Don't worry, the molds can be used multiple times. Just heat the metal back up and try again. It usually takes 3 tries or so for me.
Step 6: Cleaning Up.
Now you'll probably need to do a bit of clean up to your casting. The edges will need to be smoothed, and any excess metal cut off. A rotary tool is perfect for this, but metal files work too. Once this is done, a bit of metal polish will add some shine.
Step 7: Final Touches.
You're just about done. Or are you? What if you want an older look to your metal? You can buy commercial products to darken pewter, but why buy something expensive, when you can do it yourself? There's a few ways to darken pewter. One is to put it in a bath of copper sulphate. Make sure the metal is clean first. It should only take a few minutes to darken.
Another way I accidentally discovered by myself. I was attempting to copper plate some pewter pendants I made. I used a copper acetate bath and ran about 6 volts of electricity through it with the pewter on the negative terminal and a piece of copper on the positive. The actual plating didn't turn out too well. I got a bit of copper on the edges, but that's it. However, it darkened the metal significantly, giving it a weathered look. I'm not sure whether it was caused by the copper acetate or by the electroplating itself. More experimentation is needed.
Play around with casting different objects and see what you can come up with. Comment below if you have any questions.
Thanks for reading, I hope you found this little guide informative.
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Trash to Treasure