THE CRAFT OF FIRE

This time we tried to make bronze, in a ratio of about 90% copper to 10% tin (396g and 38g). Depending on its alloy, bronze melts at around 950º C. But since we wanted to make the bronze ourselves, we had to go about 150º C higher, because copper on its own melts at 1085º. (Tin is no problem since it melts at 232º C.) According to our pyrometer, we had reached over 1100º C in other melts, but with only one pyrometer it's not possible to get really accurate temperature readings throughout the furnace. So we couldn't really be sure that we could reach that heat inside the crucible, and maintain it. Jorge lit a little fire in the furnace, we added charcoal about halfway up, and then added our loaded crucible. Everything started well as usual; the temperature climbed quickly. We were having problems with the pyrometer though; the wires were coming loose and it would cut out from time to time. Pretty quickly, as the temperature rose higher, we started seeing beautiful, entrancing wi...

 We did it! We cast bronze.  Even though we had previously smelted bronze and melted brass , we were full of doubts with this attempt to finally cast bronze. Would the furnace get hot enough to get the bronze fully molten? Would the molds withstand the heat? Would the bronze cool too quickly while pouring? etc.  It was such a thrill to crack open the molds and see that it worked! This was the first time we made plaster molds for such high temperatures. We mixed the plaster 1:2 with sand. And then mixed this into the water, and poured the liquid plaster into our boxes.  Following a tip from our sculptor friend and neighbour  Alex , we set some of the figures on an angle, to allow the hot gases to better escape during the casting. ( This was the angle inside. ) And then of course the wax burnout in the toaster oven, to melt out most of the wax, and then much hotter in the raku kiln to burn off the last remnants.  And then on casting day, we wheeled our Might...

This time we made bronze straight from ores of copper and tin!   After melting store-bought brass , we wanted to see if we could reach the temperatures needed to smelt bronze. Smelting is the process of extracting metals from ores as naturally found. Now, bronze is an alloy traditionally made of copper and tin, around the range of 90% copper and 10% tin, depending on what you're after. For example, bell bronze (for casting bells) is more like 80-20. My friend and neighbour Alex Moyle makes some of his sculptures with silicon bronze (which confusingly has no tin in it, but ~97% copper and 2% silicon), like his latest of Pam McConnell:   At the Pam McConnell Aquatic Centre Copper can but does not usually appear in nature as a ready-to-go, orangey-brown metal; it is more commonly found as an ore. That is, a rock with a higher-than-normal amount of copper mineral within it. One common copper ore is malachite, which looks like this: photo by JJ Harrison The copper in malachit...