Bell Casting 08
For the third year in a row at the War of the Lilies we have attempted to cast a bronze bell on-site using period techniques, following in the footsteps of Theopholis (and to some extent Andrei Rublev). The first, rather ambitious attempt in 06 started with a large bell mould and a rather incomplete understanding of the workings of a cupola furnace (built on-site) resulting in 50 lbs worth of a hot, spongy, mass of copper at 2 in the morning, minutes before a major storm rolled in. The subsequent year saw a smaller bell mould and a pre-built cupola in two sections, which probably would have worked had we known that a cupola sized for 60 lbs of bronze will not properly melt only 7 lbs.
Fun was of course had by all (we are playing with really hot fire in the middle of the night [and some would say in the middle of the 12th century]). Plus we did learn a few things. Year 3 started out with slightly less ambitious goals:- reduce the number of unknown/untested elements
- produce ANY sort of bell shaped object, large or small
- check weather for impending storms before starting the melt
With these goals in mind, two smaller hand bell moulds were made (plus one left over from the previous year), adhearing to techniques discussed by Theopholis and information gleaned off the net from various groups who have tried the same thing.
Bell Core
These were turned on a bell lathe as described by Theophilus. The core was clay with high amounts of sand, sawdust, and organic fiber. The first layer on the wax was 1/1 charcoal/clay, and the outer layers were 1/1/1 clay/sand/fiber.
Burnout
The mould was burnt out in a small fire for about 5 hours.
Crucible Furnace
We used the lower half of the cupola furnace as a crucible furnace (with a modern graphite crucible) by filling it with sand to raise the crucible up to the hot zone just above the tuyeres. It worked rather well, and we had a melt in about 45 minutes. Unfortunately, to get 7lbs of scrap copper in a 7lb crucible, you have to keep adding bits every so often as it melts down, so the first melt actually took something like 2 hours total.
Furnace view
Since the glassworkers were in the tent next door to us, they provided an interesting look at the furnace with some Dydimium glasses.
Cool action shot of furnace
One of many exciting action shots of the furnace in use. We attracted people from all corners of the campsite by the glow of the fire and this huge spout of flame. We also nearly set a nearby tree on fire, but that's because they cramped our space. Mighty bronze-casters need lots of room to play.
Removing the crucible
Removing the *very* full crucible from the furnace. Note that I had at least enough sense to put some jeans and boots on under my tunic. Kids, don't try this at home.
Pouring
Minutes before the pour is where some degree of pandamonium broke out amongst the mighty bronze-casting group. As the mould was taken out of the mould-fire and placed into the sand pit, the top broke off. Panic set in as 6 hours (plus 2 years) of preparation and 4 bags of charcoal started dissolving away, however after some minutes of debate, I placed the mould in the pit, covered it with dry sand, then placed the top back on and gingerly packed it with wet sand and tamped it down. Surprisingly, this part of it held together and poured wonderfully.
The board you see seperates the 2 halves of the pit. After the pour, the board is removed and the sand pushed into the other pit to clear the mould for removal.
Well... 1/4 bell is better than no bell
Unfortunately the bottom broke out of the mould during the pour and most of the metal filled up the void in the center of the core. We were not completely disappointed, having leared several things and having another mould waiting for the next night.
End Result
Here you can see the rim seperated from the waste, and how it indeed filled up the core (you can see the markes where rope was used inside the core for initial filler). It seperated at the bottom of the rim where the mould was thinnest.
The bell-metal (copper + 22% tin) turned out much more silver than I expected, however when I polished some it did have a pleasing slight goldish-silver hue. I plan to cast some jewelry from it.
At this point (well the next day) I began strengthening the other mould at the points of failure. See the next article Bell Casting 08 - 2.
Second Pour
Here is the second pour. Looks pretty good, however...
Holes
Apparently the core shifted some and as a result there is a large hole. Looks good from one side though.