What I actually did on the foundry at Kentwell

This year, we had four of us, all having been to Kentwell before, and two with well over a decade each under their belt.

I was head of station, and often referred to the others on the foundry as Master Alexander. Which was especially nice when I had just corrected something or made a useful comment about things. My many years experience has given me a good foundation of knowledge.

The great thing about having experienced people there was that all I had to do was mention a few facts and answer their questions and they immediately incorporated it into their spiel. I was initially a bit stressed on Sunday because it was the first day and I didn’t quite know what I had, but the three of them swung into action and by Monday were talking convincingly to school children about various things.

The week did start a bit badly, because I found on Saturday night when dropping my stuff off (After driving 430 miles, so a bit tired) that someone had adapted the furnace to look like this:

Kentwell 17 furnace front top

It’s the oddest bodge job I’ve seen for a while. After fuming for a bit I worked out that we would be better to reduce the volume of it using old bricks and bits of tile and such, and scavenged them from the foundry and the pottery.

Which turned it into something like this:

Kentwell 17 crucible in fire2

Much better, you can see the bricks and tiles at the front filling up the volume. The greatly reduced volume meaning we didn’t have to try so hard to blow the bellows. Some fireclay was also plastered around the outside to block holes.

After fiddling about a bit on Sunday it was time to start working properly on it on Monday, and so we put a load of charcoal in and started blowing. It took two or three hours for it to warm up properly, presumably because of how cold the stone and such were, and how damp.

The trick during the rest of the week was to control our use of charcoal too, since it quickly became apparent that the furnace burnt it quite quickly. It was however very useful to find that the furnace retained a lot of heat if we left the charcoal in it. The next day it was still hot inside, almost too much so to touch, and this made heating it up much easier. We would use about 8 to 10kg to melt up to a couple of kilos of bronze, with enough left over to melt a few hundred grams for a second casting.

One issue is the perennial production of sparks when you put charcoal onto the furnace. The stuff we had was pretty good, and didn’t spark too badly, but it would be dangerous to anyone standing nearby in modern plastic based clothing.

For the school parties on a route we tended to put a few bit of wood inside and then blow the bellows for sparks.  The woodsmen were really good, bringing us all the wood we needed.

The actual bronze casting was best done on a freeflow day. This is when school parties can move about the manor as they wish, stopping at different places according to their whim. It means they can get more out of specific stations that the children are interested in, rather than having to move on after 4 or 5 minutes. Unfortunately timing bronze melting and casting is tricky, so we never had large crowds, but those we did have loved it.

This is also why I like to do one big melt and pour, followed by some smaller ones 10 or 15 minutes later. It enables us to use the charcoal better, and increases the chances of having some success.

It does require a bit of care though, insofar as you have to be warming up the crucible for the second melt and the associated moulds at the same time as the main melt. This sort of work is a two person job, one on the bellows and one watching the fire. You don’t have time to talk to the public, which is where the other people on the foundry are essential.

Here is the half a bell, which proved to us the necessity of working out how much metal you need before the cast, but also that we needed a new, bigger crucible (It’s about 4 inches across at the top):

Kentwell 17 half bell

The more observant of you will have noticed that it is sand cast. That’s because we didn’t have anything to make the proper clay based moulds with, you need strickle boards and lathes and stuff. Also, since the year was 1600, that’s pretty close to the use of casting sand at the foundry in Exeter, which changed over to it around the 1620’s, IIRC. Therefore I had no qualms about doing it this way this year. Plus it is easier to try and get used to, essential when people don’t have so much experience. In fact too much water was added the first day to the sand we had when mixing it, and it took a couple of days to dry out so we could use it.

We did manage to make two new bells too, small ones (half the size) using an original bronze one as a mould. You have to leave the bells to cool for a long time, perhaps an hour or two, and we left the first one overnight, because it looked like we hadn’t poured enough bronze into the mould, therefore it would be more fun to open it in front of the public and have an argument about whose fault it was that it hadn’t work.

Instead, we were very happy when we found that the bell was okay and had a nice sound to it.

One of the restrictions we had to adapt to was that as the pieces of charcoal burnt down in size, there were too many of them and they got in the way. They reduced the distance the blast travelled into the furnace. It was a good idea to start with large pieces, 3 or 4 inches across, which would then burn down to an inch or two and thus get tightly packed together, creating a decent sized hot zone between the two nozzles. Because of the charcoal burning down to small bits, after half to an hour of blasting, enough to melt metal in a large crucible and a small one, the furnace was choked with small bits of charcoal, making it hard to settle another crucible into the charcoal, as well as blocking the blast a fair bit.

Once the furnace had been dried out and we had adjusted to the best way of using it, the melting went quite well, especially using ready made bronze, which would have melted easily by 1000C. We also knew from the last two years that really a lid isn’t necessary for the furnace, and it is also possible to over blow it a lot and lose heat that way. So blowing more gently is a good idea, you can tell how hard from the sound and the look. You are always looking to see what colour the charcoal around the crucible is, red to yellow is good. White is really too hot, red not hot enough.

We also made some lead ingots for use around the place, from a small lead cannon ball, casting into sand.  Also some bronze ingots from broken up bells.  It is difficult to safely break up bells, but after an initial near accident, we managed it with a sledgehammer and anvil.

Here is Alastair casting bronze ingots, note the yellow hot crucible:

Kentwell 17 ingot making

The pewter casting went quite well too.  I tried to tin the cauldron again, but although it went better, it still didn’t bond well with the bronze so I was able to peel it off the inside.

What didn’t work so well was the lost wax manufacture of small items, as usual. Nothing wrong with the clay, just the usual issues with in-gates, metal not running in properly due to not being quite hot enough, etc.

Here you can see a few items, on the left a wax purse bar and wax key, and on the right, actual items produced.  The key might be useable, and maybe the seal at bottom right, possibly the purse hanger at the middle:

 

Also the zinc fume when melting brass was a little worrying, but we survived. There isn’t that much written about it in historical works, although you were informed that you could collect the condensed vapours from inside the chimney.

Finally, I made and sold some spindle whorls, all of pewter though. People didn’t want the heavier lead versions. Here they are, variations on a moderately uncommon design:

I managed a 14th century one too, in pewter and it looks quite realistic as well, compared to the original which has been battered about a lot:

Anyway, more on spindle whorls later, when I’ve made more moulds and cast more of them and have a better understanding of the best way to do it all.

 

Finally, a slight disappointment was how easily the outside of my brand new modern crucible glassed up:

 

It is still structurally sound, but for how much longer?

That aside, it was a good week and I think it worth doing the foundry one more time, perhaps managing to make more bells, a small cannon or two, and a mortar and pestle.

 

 

 

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