Tin and building works – what is it for?

I was having a quick look through “The Welsh castles of Edward I”, by Arnold Taylor, when I found mention of the purchase of 160 pounds of tin for use in the building of Beaumaris castle in Anglesey in the late 13th century.

This naturally had me wondering what use tin was in building works. Tin is a weak metal, and not much use by itself. Almost every use requires it to be alloyed with something else. Lead and tin make pewter, tin and copper make bronze. Actually quite a few nice shiny pilgrim souvenirs and ampullae used nearly pure tin because of that shinyness. But you don’t make them for building a castle, gold and silver are much more popular with the workmen.

You certainly don’t put it in the lead for roofing, that would make it stronger but also less able to be beaten out into shape and around corners.

The last use I could think of would be tinning iron nails or other ironwork. Not only does this make it shiny it also helped inhibit rusting.

Theophilus, writing in the 12th century, recommended tinning iron nails and sheet iron used to bind wood together for making an organ. Biringuccio in the 16th century uses tinning on the inside of bronze or copper vessels to ensure that they do not taint food. He no doubt would have tinned iron as well had it been his job.

I also think that some small or large copper alloy castings were tinned to make them look like silver.

So I think the most likely use of the tin was for tinning nails. I have tinned nails before, using Theophilus’ recipe, but it is trickier than you would think, I really should have another go at it.  This photo shows the tinned nails.

tinnednailslanark08

You need a deep crucible for the liquid tin, nice clean iron nails, and to get the temperature of the tin and nails just right, as well as a steady hand when dipping them.

 

Since I wrote this wee post, I have found a mention of using tinned nails in buildings, but cannot recall where I read it.

Interesting article on Viking/ Scandinavian casting methods, compared to what I know and have done

http://web.comhem.se/vikingbronze/casting.htm

It shows a number of things. One is that you can do casting with a comparatively small and simple hearth, with bellows feeding a tuyere. This is not of course news to many people, but it does also indicate the sort of improvements in technology that took place over the following 500 years as furnaces got bigger and bigger. Yet they could make some sophisticated and high quality items on such a small fire.

The hearth is clay lined, on stones, very simple to make, and only about 6 inches long.

He mentions some of his experiences, 15 minutes to melt a crucible of bronze is about right, I’ve done it in that time on my small setup. There is a photo of a double hearth, with one suggested for the melting, and one for heating moulds. I usually do both in the same hearth, which if it is large can mean losing a mould in the charcoal. Otherwise I just put a firebrick at the bottom at the far end of the oblong hearth, and thus less charcoal builds up there with less air getting at it, which ensures a lower temperature there, ideal for moulds.

He spends some time on the moulds, going over the advantages of lost wax casting.

It seems the crucibles were made from sand tempered clay, which is always good, but you could only get one or two meltings from each one, which I say is because it is hard to get the right sort of clay, he points out that the crucible turns glassy when used. If you use a whiter high alumina clay then it doesn’t get so glassy, but a high iron one glasses up very quickly. He then says that he uses sand tempered stoneware clay, as far as I can see stoneware clays are for higher temperature firing, and thus are more heat resistant, so of course that is what to use.

Interestingly potters have evolved their own separate nomenclature that is not directly based on scientific analysis, so they say stoneware or earthenware or describe a clay by it’s type of firing and colour.

Now, one of the interesting things is that he says the mould (made from clay, sand and horse dung) should be completely burnt through, with no organic matter left. This is partly to ensure that there is no unreacted lime within the mould, from the clay. Yet he says that this is in contrast to the historic moulds, which are often poorly burnt, oxidised red on the outside and black through the middle, which can make the casting hard to do. The reasons he suggests for successful casting are that they used zinc copper alloys which were better at getting into the moulds through being less viscous and having a lower temp.

Importantly he notes that the clay mould conduct heat slowly, so you have time to take it out the fire and pour into it without rushing, which is a good point. This also permits the manufacture of finely details pieces, because the metal stays liquid enough to get into all the corners.

Clearly I have a lot of practise left to do because my castings don’t turn out the way his do. The secret is in the mould.

Latten maille and the uses of brass in war

And lots of other latten in war gear.

I was browsing through “The medieval inventories of the Tower armouries 1320-1410”, a PhD thesis by Roland Thomas Richardson (Which can be downloaded from the British Library ETHOS service), when I found various mentions of latten. Latten in that period was a copper alloy with mainly zinc and other elements.

Quoting from “Medieval English Industries”, page 82,

“The contract for the mid 15th century effigy of Richard Beauchamp in St Mary’s Church, Warwick, specifies “the best latten”, and analysis has shown this to be a copper-zinc-lead-tin alloy: 84.3% Cu, 9.4% Zn, 2.2% Sn, 1.4% Pb, and the remainder including nickel, iron, antimony, arsenic and silver.”

It is attested as being hard as bronze, and shiny.

Thus one of the uses mentioned by Richardson from the inventories, is to decorate the edge of maille shirts, which you see worn by quite a few re-enactors, the shiny brassiness showing up well against the darker iron or steel. (page 39 of the thesis)

Cap a Pie, who sell maille for re-enactors, sell individual rings for making your shirt or standard look prettier: http://www.capapie.co.uk/index.php?route=product/category&path=59_75

Weirdly though, in the Tower inventories and accounts, there is mention of latten maille shirts! A shirt made completely of latten would not be as strong as iron or steel, so I wonder why. (Pages 41 and 44 of the thesis)

The other use on armour is as a latten border, presumably some sheet riveted onto the iron vambrace (page 78 has a photo)

Latten also crops up as horse armour.

Oddly it is also used, e.g. on page 110, to make fletchings for springald bolts! I presume that they were better able to cope with the stress of use? The other use related to springalds is in 7 nuts of latten, purchased for making 7 springalds. I think the nuts they mean are the ones that hold the long brass rod which is turned to pull back the arms of the springald. Thus they would have been large, strong nuts. (page 111)

Page 167 – There is mention of 10 moulds of latten for casting lead balls for firing from guns. Ten is quite a lot and would enable fairly rapid production, although each mould would surely take a minute or two to cool down when cast into, due to the lead taking a long time to cool.

The title though is a bit of a cheat – what they called brass usually included bronze, the latter word not being around in medieval times. So cannon were made of brass, only they meant the strong 10% tin-copper alloy. There is several mentions of them in the inventories, and usefully, of the people who made them.

Page 166 mentions a small gun of copper purchased from John ‘brazier of Cornhill’ in 1361, and of course by copper they must mean bronze, since only that could take the strain of the gunpowder. Technological terms then were not as definite as they are now, although at other places in the accounts the guns were said to be made of bronze. A brazier was basically a foundryman, someone who cast in bronze or indeed brass, into moulds, whether of stone or clay or suchlike.

The earliest accounts I know of from Scotland of such practise are in the reign of James IV, the 1490’s, when a potter made a mould for casting a gun in. A potter being someone who made metal cauldrons, i.e. pots. There isn’t that much evidence surviving for potters in Scotland, but there must have been some.

So, it is amazing what turns up in peoples research. I urge you all to search through ETHOS to find PhD theses of interest.

Trying to make a lead spindle whorl and mould

For several years now I have been trying to make various replica pewter and lead objects, one being a spindle whorl. Not perfect copies cast from an original in silicone, but copies of the sort that a foundryman might make after seeing an object. Of course the process of making the object can also teach you something about the manufacturing capabilities of the time and confirm or disprove how you think it was made.

Spindle whorls are the weight which keep the spindle turning when you are using a drop spindle to make thread, as was common throughout the medieval period and into the 17th century. Excavated examples include ones made of wood, pottery and lead and obviously I am interested in the latter.

Of course nobody seems to have written anything about how they were made, except it is obvious that they were cast. I have examined 5 myself, and the portable finds database gives access to photographs of many others, of several main types amongst the hundreds of examples.

E.g. :
https://finds.org.uk/database/artefacts/record/id/730362

The PAS finds 1,737 medieval lead spindle whorls, which is probably a small fraction of those found over the years, nevertheless it indicates a huge number of them.

Unfortunately the first attempt I made 5 years ago now involved casting plaster and a spindle whorl:

large spindle whorl

It didn’t really work, casting plaster is trickier to use than you think, especially when the whorl is of such an odd shape.

A friend lent me a smaller simpler whorl several years ago, and I’ve been carving since then.

This is it side and top view. Note how well rounded it is, which might be due to wear or the method of casting: Continue reading

Being a blog, I can ask questions that professionals won’t go near due to lack of evidence

For instance, who made stone moulds used to cast pewter and perhaps bronze items? Having had a skim through several sources of information about stone moulds, such as the Museum of London books, the Historical Metallurgy Society journals and excavation reports, I can’t find anything about this question. Of course being a proper careful archaeologist you can’t go beyond what the artefacts tell you, and they mostly don’t come with labels or engravings saying “Made by Bob”.

Obviously carving stone is a specific skill associated with masons, but the moulds are quite small and were probably carved using small sharp tools and files. My experience of making them suggests that with a modicum of artistic ability and fine motor skills you can carve moulds reasonably well, but the complex ones for pewter badges will take quite a lot more practise and real artistic skill.

Which therefore does not mean a stone mason is required.

One suggestion, in “English Medieval Industries” (page 78 of the paperback edition) is that many of the more detailed pewter badges were cast in metal moulds, the metal being cut by seal engravers. Who would indeed have the requisite skills, but I would need more evidence that they actually used metal moulds for this sort of thing in the first place, given the stone moulds that we know of from Britain and Germany, and the fine detail you can get in any fine grained rock.

I did read somewhere that the earthen moulds for casting bells and cauldrons and suchlike in, were made by a specialist on making them, referring to some records from medieval York, but those were single use moulds and he would have made scores every year, whereas a good stone mould can make 300 or 400 pewter castings and thus last for years of use.

Certainly engraving metal moulds would be harder for foundrymen to learn and do than simply outsourcing the work to someone else, but on the other hand they might, especially in smaller towns, encompass engraving within their skill set, as it is in a way related to the finishing of small items.

Turning to “A History of British Pewter”, we find mention of moulds in wills, but unfortunately it does not say what the moulds are made of. Some will be bronze, for plates and the like, and maybe they all are, or maybe some are stone. The authors write that metal moulds were widespread in England in the 15th century, attested to by references in the London Pewterer’s records, in Welch, i, 14-15, 105, 120, 175, 179. Welch is “History of the Worshipful Company of Pewterers of the City of London, 2 vols, 1902. (Note to self, the NLS and St Andrews and Glasgow have it) They also assume that the pewterer would make his own moulds. It would be comparatively simple for a pewterer to cast their own moulds (Or got a foundry to do it, but in smaller towns they were often both the same person and workplace), and spend time finishing them off. It would certainly negate the need for an engraver.

In fact, having been spurred on by this question to read more, I have an answer in the book “Pilgrim souvenirs and secular badges” by Brian Spencer, one of the Museum of London books. It says in the introduction that “Little is known about the men who made the moulds, an operation that called for skill in small-scale precision work as well as a degree of artistry and iconographical knowledge.” It seems some records in York and Cneterbury mention mouldmakers, i.e. people who carved the moulds, whether stone or also, as is shown in the book, cuttlefish bone, but it is not always clear in the records whether they made their own mould or hired them. The introduction also mentions the use of seal engravers in mould cutting and goldsmiths and that bronze moulds for casting pilgrim souvenirs are also described.

So we have more of an answer than at the start of this post. With any luck there is more information available; I shall certainly be chasing up the excavation reports of the moulds mentioned in the book. Cuttlefish bone is one substance I haven’t really looked at, but will surely be the subject of a blog post in the future.

The rather important use of lathes by foundrymen

For 7 years now I have been thinking about all aspects of how medieval craftsmen made objects out of bronze or pewter. The method of manufacture of some objects is obvious, from the excavated stone moulds for pewter badges through to the methods of making bells, which are recorded in detail in the 12th and 16th centuries, with nothing much changing in between.

But that still leaves some items unaccounted for. Some, like small bells, are made of sheet metal or else have cores of sand and clay within a stone mould a bit like that for making bullets, but nobody has left instructions for their manufacture.

Others, like mortars and pestles, well, eventually I worked out that they were probably made the same way as bells, and lo and behold, in Biringuccio’s book it says that you make mortars, basins and other vessels which need to be hollow in the middle in the same way as bells (page 268 of the paperback Dover edition).

This means that a founder needs a lathe of sorts in order to turn the core of the mortar.

I did in fact first try to make a mortar by having a wooden pestle and a mortar made, which could then have the earth pressed around them before removing them and sealing it all together, but that proved to be harder to get right than I thought. The pestle I did produce had a lot of flash down one side because the dampl clay was not rigid enough to stay perfectly in shape when I was taking the former out, and the mortar mould has not yet been tried due to the slowness of mould manufacture and drying and issues with melting the metal.

Anyway, what did lathes look like then, of the sort I can use?

Fortunately there are pictures and descriptions, but never enough. Continue reading