I have gained some useful experience at Kentwell Hall in Suffolk, bronze casting the 16th century way whilst dressed in funny clothes.
Writing all about how to cast bronze would take a book, albeit a small one. (any suggestions for who might be interested in publishing such a book are gratefully received. I’ve already asked Shire, they said no)
Instead here’s some pictures of fire…
This is the Foundry itself, based upon one pictured in Biringuccio’s 1540 book on foundrywork. You can just see the bellows and in the middle under the roof, the brick wall on which the furnace is based.
This shows the lid of the furnace, with orange flame coming out, indicating that it is just warming up, and the bellows are hardly pushing any air through at all.
Because when you do step up and down on the 6 foot long bellows, it looks like this:
Like a rocket engine. The flame is bluer too, indicating that there’s better combustion taking place, and less soot than in the orange flame. But it can also look quite blue, due to CO from the furnace, carbon monoxide, burning in the open air. Flames are very complex things…
Anyway, once the furnace is going well we put the firebrick on top of the hole in order to reduce the amount of heat that escapes. Without it lots of heat is just radiated straight out of the hole, but with it blocking the heat, more stays in.
Here are two of us raising the lid. Note the leather aprons, necessary to stop us being burnt by the heat given off. The interior of the furnace is at around 1200-1300C at that time, hot enough to burn your skin if you put your hand near it for any length of time. An experienced foundryman can tell by the colour of the fire how hot it is, and I have just enough practise to get a good idea. Unfortunately in this photo you can’t see the charcoal. That will be the subject of another post.
He made a bell!
But to get that far took several hours of work. First lighting the furnace, letting it grow, get hotter, half an hour or so bellowing to melt the metal. Plus another half hour of work to make the sand mould.
The small drawback in trying to get pictures of hot things is that if you get too close your camera may melt. These photos were taken hastily as well; regrettably because of our amateur status we often managed to get the casting done after the public had gone, although most managed to see it all being setup and the flame.