It was so exciting, like going to a carnival as a child. For the majority of my class it was our first time seeing molten metal cascade down into plaster. It was our first pour! Luckily, the metal shop at The Evergreen State College has their very own foundry and tools for students to use. But let's back it up a little bit, there were multiple steps that we had to take to ensure our bronze pieces came out well with minimal bubbles and flashing:
Step One
The first step for my class was making a silicone mold of the objects we would like to bronze cast. Once we had silicone molds, we made a plaster mother mold that holds the silicone molds’ shape while we pour wax inside the silicone.
Step Two
Once our molds were ready we began casting as many wax replicas as we could within a week and a half. While our objects were in wax we had the potential to cut up, rearrange, clean up, or otherwise alter the moulded shape. During this wax process, possible potential areas became apparent with the initial silicone mould, such as flashing, when liquid leaks out of a crack in the mould or an arm not filling up with wax completely.
Step Three
Once we were satisfied with the waxes we had produced from our moulds, we began spruing the waxes. The sprue system looks almost like an ant farm, wax tubing with objects attached coming off from one main tube, like a main ant tunnel and lots of hallways leading away from the main thoroughfare. The wax decides how the plaster holds it’s shape as well as where the bronze will pour, it is the path the metal will take.
Step Four
Now that we have our sprue systems, we took chicken wire and cardboard tubes on a flat board, we filled the chicken wire tube with plaster while holding our spru system inside of the tubes. The plaster tubes with the sprus are set out to dry overnight.
Step Five
The plaster tubes are placed within a special kiln that is heated to various temperatures over the weekend to melt the wax out of the plaster and to keep the plasters at a particular heat.
Day of Pour
We are ready to start heating bronze ingots, bronze bricks, some of which have been used in previous castings. There is an old wives tale that you always put in 10% fresh bronze to maintain the Tin content. Bronze is a mixture of copper and tin, tin heats very quickly and evaporates faster than copper, that's why fresh bronze is needed.
We began heating at 10am after our class went through a dry run of the pour so everyone knew what they were doing and where to stand. The bronze took almost five hours to heat up to the correct temperature and melt all the ingots.
The day was special, there was excitement and nifty safety gear to wear. Once the bronze was at the right temperature we brought out our plaster tubes and placed them on the ground to fill with metal. Now it was go time, everyone was quiet and paying attention, we each did our job like we practiced in the dry run. The actual pour was less than twenty minutes long. It was like christmas morning, after months of build up and planning, every present is opened in seconds and now it is over. For most in my class this will not be our last pour.