THE CRAFT OF FIRE

We were looking at different kinds of bellows that we might use to get higher temperatures in our bronze clay furnace. And in the end we decided on box bellows. It seemed like it would be fun to build, within our woodworking abilities, and also provide enough air. We also liked how they were rather a different design than the accordion or bucket bellows that we thought were more typical. In essence, it's a box with a piston that draws air in and out, and inlets with flaps that allow the air to flow down and out by the path of least resistance through a tube or nozzle ( tuyère ) at the bottom. The end of that nozzle is in your furnace or forge. Our bellows is made out of pine.  An old vacuum cleaner tube serves as the tuyère. Here are the holes for both ends of the box. All the holes get covered with a heavy fabric flap, which forces the air to go in but not back out when you draw the piston out. It took me a while to figure out how to make a hole in the middle of a piece of wood. I...

We had these molds that never got filled from our first bronze casting session , so we bought some brass at Metal Supermarkets , loaded up the crucible... ...and got to work. We started just before 2pm and the fire and charcoal took a little while to catch as usual, but by 2:30 there was lots of flame so we filled the furnace up.   Close to 3pm, the brass was softening but not melting. We then covered the whole thing with charcoal, crucible and all, and waited about 10 more minutes. So from starting the fire to having molten brass, it only took an hour (pyrometer reading was 1067).  But before we pulled the crucible out for casting we needed to scoop out as much of the charcoal dross as possible.   I made a little spoon device which worked more or less; we tried scooping out the dross without also scooping out the metal, but it wasn't so easy. We scooped a bit and then just went ahead and cast: We each cast our own, putting the crucible back in the furnace in between pour...

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...