The Must-Try Method for Pewter Casting with High Temp Silicone Mold
February 21, 2019
Working with low melt metals, like pewter, can be really fun! Pewter (and other alloys containing bismuth, tin, and lead) have low enough melting temperatures that you can cast them at home or in a workshop with having to buy or build a foundry. Thank goodness! I am tired enough from searching for a replacment for Valentine’s Day candy hearts. Back to work now (sadly not fueled by sweets). With these types of low melt metals, you can use our AeroMarine Products 150 High Temp Silicone for casting instead of expensive graphite or iron molds, or temporary sand molds. I am casting a large, rather intricate fake antique key for this project, so I will be doing a two part mold. This is my first time casting pewter! I am excited to see if casting pewter is as easy as it looks and what the pewter is like as a casting material.
- Object to cast (My fancy key, in this case)
- AeroMarine Products 150 High Temp Silicone Rubber
- Sulfur free molding clay (like plasticine)
- Pewter, or other low melt metal
- Mold release to release silicone from silicone, like our Petrolease Aerosol Mold Release or petroleum jelly.
- Small plastic bits to use for vents and pour spouts; cut up drink stir sticks work well.
- Mold box. I used a small candy tin. You can also use Tupperware or make your own mold box.
- Plastic measuring/mixing containers and plastic utensils
- Blue painter’s tape and a pen or plastic stick to make registration marks in the clay
- A pot or pan to melt the pewter in THAT WILL NOT BE USED FOR COOKING FOOD EVER AGAIN. In other words, please don’t use your good cookware.
- Oven mitts
Your work area:
- Clean, level work surface, covered in paper or plastic for easier clean-up.
- All materials comfortably within reach.
A quick note about Platinum Silicone: Platinum catalyzed silicone have more cure inhibitors than tin catalyzed silicone. Do not wear latex gloves when working with platinum silicone. Don’t use oil-based products as a part or in the 2-part mold process. Tin catalyzed silicone can also inhibit platinum silicone so don’t work with tin silicone in the same area as platinum silicone. Other cure inhibitors include sulfur compounds, organo-metallic salt-containing compounds, chloride solvents and amines. For best results, make sure your work space is extra clean and free from contamination. I will go over briefly how to make a two part mold. For a more thorough step-by-step two-part mold making process, read this post https://www.aeromarineproducts.com/two-part-pourable-silicone-pumpkin-mold/
Embed your original part halfway in clay, in the bottom of the mold box. Embed the cut-to-size stir sticks in the clay as well where you need a pour spout and vents. As you can see in the picture below, the stick at the top of the key is where I will pour the pewter and the stick near the bottom is to vent any air trapped out of the mold. Use the end of a pen or stir stick to make divots (registration marks or keys) in the clay. These will help to ensure the two halves of the mold fit together tightly.
AeroMarine Products 150 High Temp Silicone is a 1:1 by volume platinum cured silicone. For this small project, I measured out a quarter cup of the Part A and a quarter cup of the Part B. I poured them into a separate clean plastic mixing container and mixed thoroughly, taking care to scrape the sides and bottom of the container. The pot life for this silicone is 45 minutes, so you can take your time to make sure it is very well mixed and one uniform, even color. Once the silicone was thoroughly mixed, I picked a corner of the mold box and slowly poured the silicone. Don’t pour directly on the key. Instead, pour only onto the clay. This ensures that the silicone will flow around the key and not trap any air. Once the silicone was cured (about 12 hours later), I carefully removed the whole thing, clay, key and plastic bits, and silicone from the mold box. I cleaned the clay from silicone, leaving the key and plastic bits embedded in the silicone. I then put it back in the mold box with the key facing up. Be careful with the platinum cured silicone because this material is a bit more brittle than the usual tin catalyzed type silicone rubber.
I coated the cured silicone with heavy layer of mold release so the second silicone pour won’t stick to the first half. I mixed up more silicone and repeated the pouring process. I let the silicone cure for 12 hours and then removed the mold from the mold box. I carefully separated the halves of the mold and removed the key and plastic sticks. I enlarged the pour spout area a bit with an X-acto knife, to make it easier to pour in the molten pewter.
Once my mold was ready to go, I got ready to melt and cast the pewter. I used an electric range and an old cast iron skillet to melt down my small bar of pewter. While the pewter was melting (about 15 minutes with the range set on HIGH), I prepped my mold for the cast. I used blue painter’s tape wrapped around the mold in order to keep the halves together snugly when the weight of the pewter hits. I lined my mold box with tinfoil and used some wadded up tinfoil to make sturdy spot for the mold to sit. My mold box was made of metal. If you used plastic or cardboard for your mold box, please find a metal box, tray, or something along those lines to use for this project.
Once the pewter was completely melted, I put on my oven mitts and CAREFULLY AND SLOWLY poured the pewter into my mold. I carefully set the skillet back on the burner and didn’t touch the mold for 5 minutes.
After 5 minutes, I carefully touched the outside of the mold to see if it was still hot. It was just a little warm, so I laid it flat and cut the tape holding it together and slowly opened the mold. The cast looked okay for the first time working with this material. Not perfect, but alright. I poured a couple more casts to get a more experience casting pewter and they also turned out okay.
I think since this was my first time casting pewter, I should have gone with a simpler mold. However, I am pleased with this learning experience! You can watch a short video about this process on our YouTube channel, https://www.youtube.com/watch?v=EQk8umkAYXo
If you have any questions about this project or your own projects, give us a call, toll-free, at 877-342-8860 or send us an email at [email protected]