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

Continue reading

Tinning copper and bronze, part 1

This is something I’ve been meaning to do for years, it happened often enough in the medieval period, to cooking pots and also some buckles and the like, basically anything which would look nicer with a shiny corrosion resistant surface. I tinned iron nails many years ago, but somehow never got around to trying it on copper or bronze. It is a sensible thing to do to a cooking vessel, to ensure it doesn’t taint the food you are cooking.
So, this is how you do it, according to Biringuccio (Page 369 of the paperback Dover edition):

“To do this, a little salt and vinegar is boiled and the vessels are cleaned well inside with this. Then some tin mixed with a fourth part of lead and with some powdered Grecian pitch is melted. The tin is applied as you wish by rubbing it all over the outside and inside with a brush of tow tied to the point of a tool or held with a pair of tongs.”

I’ll skip using the lead for obvious reasons. And I don’t have any tow, which presumably would be made from flax or hemp rope. The pitch acts as a flux, helping prevent oxidation of the liquid tin and lead. I have other substances which might do, such as lard or beeswax.

In order to tin the group cauldron therefore, I set it up like this on a fire:#

cauldron on fire

It took a while to heat through due to the mass of bronze. Continue reading

Incredible sets of medieval moulds found in France

A few years ago at Mont San-Michel, a lot of stone moulds for pewter casting were found.
Here is the link

http://www.inrap.fr/preventive-archaeology/Events/Virtual-exhibitions/Virtual-exhibitions/Making-Pilgrim-Badges-at-Mont-Saint-Michel/The-site/p-1475-lg1-The-site-and-the-discoveries.htm

They are 14th and 15th century pilgrims badges, often showing St Michael, or the Virgin, or a sword. The detail and artistic skill is wonderful to see, far above my own. 260 fragments were found,

Quote:
“This excavation is exceptional in that it has revealed a workshop for the making of pilgrim badges, the first to have been found in France to date. Exceptionally, the activity is clearly shown by the objects found, the cast-offs, and the archaeological structures, even if the latter are incomplete.
It was not only a workshop for the making of finished objects for pilgrims, but also for the making of moulds for this activity, as indicated by the numerous waste products, rough mould shapes and reworked examples. The whole chain of production was on one site.

However, it is not clear why certain faultless intact moulds were abandoned, especially when it is clear that this type of object was considered to be precious and was transmitted from generation to generation. “

The above indicates a problem similar to that I have mentioned to do with the Coventry moulds, that is, why were they dumped? Many of the Coventry ones are not obviously damaged. What the article doesn’t specify is how faultless the dumped moulds were. It is entirely possible that still usable moulds would have been dumped when fashion changed. Or maybe one part of them broke.

It is interesting though that the moulds were made on the site they were used. What is unclear from the historical records and finds in the UK is whether the pewterer carved his own moulds. I think they may have done so in some occasions, but in others purchased them from stone carvers, but I am not aware of any definite evidence either way. It has been suggested that engravers did the carving, and even that some carved bronze moulds for pewter casting, although none of them have survived. Somewhere more isolated like Mont San Michele would not be conducive to a division of labour, whereas in a town it would be easier to find a good carver.

The website says:
“The quality of the engraving, characterised by great attention to detail, bears witness to the work of craftsmen in full possession of their art, but who were also dependent on the wishes of the monks of the abbey. Written sources inform us that the moulds were the property of the monks and were made at their demand. The monks then entrusted them to metalworkers for the manufacture and sale of the badges, an important part of the profits being paid back to them.”

which still leaves it a bit unclear who the monks had make the moulds and sits oddly with the fact that the casting and the mould making happened in the same workshop.

The photos of moulds that they have made available indicate the usual methods of manufacture, but what is interesting is that they are made of schist and limestone. The limestone is probably from the same source as the Caen limestone, but the schist is not so easily located, perhaps coming from Breton quarries. According to the website the most detailed carving is in the finest grained schist, which makes sense. But oddly the geology book I just consulted says that schist is a moderately metamorphosed rock, made up of very platy minerals, such as mica, which in a schist are large enough to nearly be visible to the naked eye. Which would to my mind make it not very good for carving. If it is so fine grained that it isn’t obviously so wavy and platy, then it isn’t a schist. Certainly some of the Coventry moulds are highly metamorphosed mudstones and the like.

They have the usual holes for locating pins, vents for air etc. One has a clear saw mark in it, proving that they cut the stone up using saws.

Some day I’d like to have a look at these moulds.

Books, blogs and communicating knowledge to the public

This blog as yet has few readers; perhaps at some point I will be swamped by school pupils looking for information they can steal for their essays. But thinking about it, this lack of interest is part of wider issues to do with the means of communication.

The first example is that this blog covers archaeometallurgy, i.e. historic artefacts made of metal, their manufacture and their place in society and use by people. As far as I know, the only general book on the topic written for the general public was Ronnie Tylecote’s “History of Metallurgy”, which was first published in 1976 and an updated version in 1984.

It would be nice to know there was a more recent book of this type, but people are still using it as a reference on wikipedia, and I am sure I know of an error or two in it, because actually archaeometallurgical knowledge has greatly improved since the early 1980’s. Just in Britain we’ve had the publication of lots of London digs, putting metal objects of various sorts into their context and period; in Scotland there’s the Perth High street digs. There have been numerous PhD’s on archaeometallurgical topics, and a thriving society, the Historical Metallurgy Society: http://hist-met.org/

which journal has many interesting articles on the manufacture and use of iron, copper, gold, silver etc. In fact Tylecote was the founding father of archaeometallurgy and helped found the society.

http://en.wikipedia.org/wiki/Ronald_F._Tylecote

What all minority interests have trouble with over the decades is getting funding and disseminating information. Hence this blog and my re-enactment presentations. But my self appointed task (One which is also quite fun) is made a little harder by the paucity of publicly available information.

Another example of the issue is the book “English Medieval Industries”, edited by Blair and Ramsay. Whilst it is available on google (http://books.google.co.uk/books/about/English_Medieval_Industries.html?id=PDLPX7J8kW8C) that is not a full copy, so frustratingly you can’t get at all the information.

Amazon has copies from £42 upwards into the hundreds, because it was first published in 1991 and a paperback edition done in 2001, from which my copy comes, and it cost £19.95.

So the information in it is now 25 years old!

It is a standard reference work for anyone wanting to learn more about everything from cloth manufacture to foundrywork, but the sources and such are more than a generation out of date. Whilst I think the information given and the general conclusions are accurate enough even now, any attempt at public education should include more up to date sources, which in this day and age would include web links, even although they are often subject to rot. There is also the simple fact that EMI is out of print now and unavailable to the general public; if you are luck your library will have a copy, although due to cuts that is now extremely unlikely.

Fortunately, Copac indicates that there are copies at 31 British libraries, including the NLS, NLW, BL and university libraries. So if you really want to you can find it, but most people won’t know of the fact that you can get into University libraries even as a member of the public.

To summarise – I think there’s a disturbing lack of modern public friendly sources of archaeometallurgical information. Whilst the archaeometallurgists I know will happily talk to anyone about the topic for as long as their interlocutor can stand it, there simply doesn’t seem to be much that is easily available to the interested member of the public.

There is a great deal to be found on less well known places like http://www.academia.edu, but how many people know of it? I know of no other blogs like this, although some of the old SCA websites have information and write ups from 10 or 15 years ago. A lot of information is also found by careful searching of groups on the likes of facebook (E.g. this French experiment on crucible steel, written in English – http://ceroart.revues.org/2557#tocto2n1), but ultimately I have the impression that the subject is stuck in a ghetto. We need more communication and examples and books and other sources, to let everyone know how interesting this subject is and of course ensure they are properly educated.

TV programs sometimes cover it, for instance there was that well done documentary a couple of years ago on the bronze crossbows found with the Terracotta warriors, which really put archaeometallurgy centre stage. But that is about it. A fe minutes on Time Team or such programs really isn’t enough.

Real and possible misperceptions about medieval copper alloy castings

In the rainy season I thought I’d correct a few of the odd ideas that people have about medieval casting, but the annoying thing is I can’t really find many examples of people being wrong. This is in part because the internet is not all powerful and all containing, and searching it isn’t as easy as it used to be. Some of the errors will have been promulgated off internet, in magazines or books that I have never read. Other errors have no exact source, but are what people assume based on partical knowledge.

The most common error is certainly the idea that they used sand casting, especially for cauldrons and smaller items. Apart from the lack of dumps of metal contaminated sand at excavated foundry sites, we’ve got lots of physical evidence of what they did use to cast bells and cauldrons. Yes, clay and organic muck. It survives well in the ground. For instance, at Exeter archaeologists dug up over half a tonne of clay based mould fragments from the manufacture of cauldrons, as can be seen by the shape of the pieces.

Elsewhere in the country many fragments of bell mould have been dug up, whether in London, York or elsewhere. These correlate with areas and times when the documentary evidence shows that there were bell foundries at work, and in the texts they refer to earthen moulds, i.e. not sand, but mixes of clay and other sedimentary materials.

(I just found this report on a Lincolnshire excavation that examined bell casting debris http://services.english-heritage.org.uk/ResearchReportsPdfs/104-2002.pdf)

We also have the remains of a clay based buckle mould found in London, showing that they were using it for small items as well. Since we also have stone moulds which could be used for buckles and the like, the question is, where would sand moulds come into it? Continue reading

Previous posts on foundry related topics

Here are some links to previous posts on my now alchemy oriented blog:

http://distillatio.wordpress.com/2014/06/03/the-use-of-stone-moulds-in-13th-century-germany/

http://distillatio.wordpress.com/2013/11/03/an-observation-about-medieval-buckles-which-may-or-may-not-have-any-significance-about-how-people-made-buckles/

http://distillatio.wordpress.com/2013/10/25/casting-copper-alloy-buttons/

http://distillatio.wordpress.com/2013/09/29/the-randomness-of-surviving-artefacts-and-re-enactors-having-the-wrong-stuff-medieval-buttons/

http://distillatio.wordpress.com/2013/10/25/casting-copper-alloy-buttons/

http://distillatio.wordpress.com/2013/11/13/itinerant-bellfounders-and-the-shire-book-on-bellfounding-a-critical-blog-post/

http://distillatio.wordpress.com/2013/10/20/trying-out-different-mould-materials-for-bronze-casting-its-amazing-what-works/

http://distillatio.wordpress.com/2013/02/04/bronze-casting-at-kentwell-hall/

A fair bit of reading for anyone who is interested.

Introductory post

So, an explanation about the illustration at the top of this blog. That is a bronze pestle, cast at Kentwell hall into a clay mould. The mould was made of clay, horse dung and sand, mixed together and formed around a wooden patron (a version of the finished object).

Unfortunately the end result was a little squint, due to the mould not keeping it’s proper shape when the patron was taken out. Nevertheless, it illustrates things very nicely. You have the red bloom of copper oxide halfway along, and to the right a head of metal for filling the void. It filled it well too, it wa s a good casting. Importantly you can clearly see the red, oxidised outer layer of clay, which is that colour from the oxidising atmosphere in the furnace when it was fired before the casting, and the inside is black, the colour due to reduction, i.e. not getting enough oxygen in the furnace. You see this on medieval pottery and debris from casting all the time, the red outer from iron oxide in the clay and the black inner where there wasn’t enough oxygen. It helps you piece together the moulds after they have been in the ground for centuries.

I’m going to be commenting a lot about the surface finish of the pieces as well. I suspect I’ll need to get a lathe to get anything like a historic surface finish, because in my experiences so far it has proven impossible to get a finish as good as the medieval artefacts I have examined. Some of that might be done to not casting in stone yet, but that is another technique I have to learn and make work.

Essentially, what I think is that historically/ archaeologically, we don’t know the past well enough until we can re-create as much of it as possible at will as closely to the material culture and artefacts of the period. Some might argue that we’ll never get perfect accuracy, but I think that is a pointless claim, although it might be technically correct when you get down to the precise chemistry (E.g. there are few modern sheep with wool anything like medieval ones, so reproduction cloth won’t be quite right), it ignores that we can know and be sure of a great deal without any problems, and part of that is knowing that there will be differences in behaviour between medieval and modern cloth.

Hopefully you will follow me as I get better acquainted with how our ancestors did things, and the skills they learnt and used, as well as the exciting stuff like molten metal and fire.