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Making More Bronze (Session 7)

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(cracked mold with a drop of bronze inside) For our first session this year (the weather has not been cooperative), our  plan was to make more bronze because we're almost out and we have lots of plaster molds (made over the winter) to fill. So we loaded the crucible with copper and tin, 90:10. in the hope of making bronze to cast it in our patiently-waiting molds. (NB: I realized later, though, that our 90:10 calculation wasn't quite right. We measured the 10% tin in relation to the amount of copper we had, but I think it should be in relation to the final amount of bronze we'll end up with. So we may in fact have been short about 6-7 grams of tin for a true 90-10 ratio. Would that be significant? Would it have helped bring the liquidus temperature lower?) Many of the molds were cracked, as you can see. It was more than likely that they got too hot too quickly in the kiln, during the wax burnout earlier this year. (The sprues are covered or stuffed to keep them clean before...
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We're Learning! (Bronze Casting No. 6)

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Our most recent session was the culmination of the whole process involved in casting a new object: new rubber silicon molds, wax patterns, plaster molds, wax burnout, bronze melting and finally, casting. And we have the wonderful feeling that we're learning. We wanted to cast a new pinecone and some acorns, too, and also a small medallion with the symbol of the School on it. These were the objects for which we needed entirely new rubber molds. The medallion was a real challenge because the engraving is very low-relief - we weren't at all sure if we could capture it first in rubber, then in wax, then in plaster, and finally in bronze. We made up our molds - medallion, pinecone, acorns, and a new salamander, too, because we had some extra material. And then we cast them using our newly made wax . We put two acorns together to improve our casting odds - maybe at least one would turn out. (image is there, but barely visible in wax) Next we made up the plaster molds, mixing sand and...
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Bronze Casting Session No.5

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Last time we melted and cast bronze , we figured we had to build a new furnace since, after ten firings, ours had a serious crack in it. But then we thought, instead of doing all that work, maybe we could get away with wrapping ceramic fibre around the furnace. Here's how it went. We loaded up our crucible and set it into the furnace after the charcoal was burning well. And then we piled on the charcoal to completely cover the crucible, and waited.   When we first melted bronze and brass , we didn't need any external air source; the natural draught provided by the three entrances along the bottom of the furnace were sufficient. But since then we haven't been able to melt bronze without adding forced air from bellows. Perhaps we haven't been loading the furnace with charcoal correctly, and the entrances at the bottom are getting blocked by small bits of charcoal. Perhaps it's time to re-read the original paper that guided our building of this furnace. However it is,...
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Making Colophony (Pine Resin)

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There's a cemetery near my house where I regularly walk my dog, and in it there's a Norway spruce tree that produces a lot of resin.  Over time, I've collected it, thinking that it could serve when we make casting wax. Here's a nice, clear piece: Our recipe for casting wax is 70% beeswax, 20% paraffin, and 10% resin. In the past we've used store-bought gum arabic or damar but this time, we decided to use this cemetery pine resin. (We tried using a resinous substance from a Kentucky Coffee Tree  once, but it didn't work.) First, we needed to get the resin ready, cleaned up as much as possible, purified of bits of bark, insects, and the like. I heated it up with a double boiler, assuming it was safest to use gentle, indirect heat on it.  It didn't take too long before it started to melt. There were some chunks, though, that took much longer to dissolve than others, even when I put the pot directly on the heat.  In the end, even when everything was boiling away...
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