Melted copper and disaster

Today I managed to melt some copper and break my bellows.
On Friday night I had set up my furnace, with rather a large furnace volume. On Saturday morning I lit the charcoal, and realized that it was not going to work, since the bellows were too far from the charcoal and the overall volume was too large, the charcoal would spread out too easily. So I pushed one end in and swapped the bellows round to the other end. Doing this meant the hot zone was barely 10 inches a side. I keep forgetting how small is better in this situation. Furnace performance depends upon the fuel supply, and how much air you can get into it, so if the internal volume is very large, you cannot get enough air in to keep the charcoal burning fast enough to produce the heat needed. A bit of wind will get you above 5 or 600 degrees, but in order to get to high temps you have to get bellows blowing straight into the heart of the fire.


This is what the set up was like:

My bellows are tied onto the wooden collapsible stool I have.
This is the raw material:

Copper wire and bits off the end of pipes, placed in a small crucible. I was hoping on getting a puddle of copper in the bottom of the crucible, which required a temperature above 1083C, the melting point of copper.
So, after some puffing with the bellows, I managed to get the temperature around 1100, and held it at that, or as high 1140 or so, for several minutes at a time, pausing only to add more charcoal. This was small bit of charcoal, maybe a cm or 2 long.
This is what it looked like at that stage:


The green bit of wire to the left of the picture is the thermocouple probe- several feet of plastic coated wire attached to a stainless steel sheath encasing the thermocouple wires. The problem is, that to maintain that temperature, and a high of 1180C (Any more and the thermocouple would have been damaged) I had to work the bellows almost constantly, and also throw on small lumps of charcoal at frequent intervals. I could follow the temperature changes as the smaller bits of charcoal were consumed. At one point I was holding around 1140 with only slow puffing of the bellows, for several minutes, but then the temperature began to fall, and I think it would have been due to the higher surface area small stuff having been consumed, leaving only the larger bits that would burn away more slowly.
So this went on for half an hour or so. All I could see of the crucible with the copper in it was the top of a bit of pipe, which had clearly not melted. Which was annoying, so I kept pumping the bellows, trying to maintain a high enough temperature.
Then I smelt something burning, which was odd. I knew the copper pipe out of the bellows was getting hot, I had already dowsed it with water several times. But this was a fishy smell….
Then the bellows went a bit funny, and I knew something was wrong. It turned out that this hole:




Had been burnt in them. It looked like I had managed to suck a small bit of charcoal back into the valve bit of the bellows. Now, several times during my puffing I had heard sounds like hot air was being drawn back into the bellows through the copper tube. It seems that maybe I was not drawing the bellows in the right way, although it is not clear how.
So, this is the melted copper:



Not much, is it? The lower bits got hot enough to melt when they were touching the crucible, but the temperature never got hot enough for long enough that the upper bits melted into them. However today’s experiments show that it is possible to get high enough temperatures to melt copper, which is therefore high enough to make various copper alloys. It’s the glass making that will be tricky.

I need to get the bellows fixed and get a second pair. In the meantime I can play with pewter casting, since pewter will melt over a good charcoal or wood fire, the modern Britannia metal variety melts around 210C.