Casting Hollow Forms in Tin

My first hollow form casting in tin: based on three Canterbury pilgrim’s tokens, holding a pencil (it was the site token for an archery and thrown weapons tourney).

I recently learned a new thing (to me) in low-temperature casting: hollow forms cast in tin. It’s a medieval practice, easily documented, and used for an exciting variety of forms, including ampullae, whistles, bells, wearable vases, and even tiny reliquaries, as ten minutes of happy searching through the Kunera database showed me. (Go look for yourself! It’s awesome!)

The pewter I ordinarily cast with is 98% tin, but that 2% makes a difference. Pure tin stays liquid longer than pewter, not going through a ‘slush’ stage as it cools. This means that it can be poured into a mold, then dumped out, leaving a thin layer of hollow metal in the mold.Tin tends to be a bit softer than the pewter I use, but not prohibitively so.

Why would you want a hollow form instead of a solid one? With some things (bells and whistles), it makes them work as instruments. Ampullae and reliquaries are intended to hold material from a sacred site or person, so a hollow is essential. Of course, a hollow item is also cheaper to produce, as it uses less material.

A mold for a hollow form isn’t much different from one for a solid piece. If it will be two-sided (having carving on both faces) or even more complex, the mold will need to be fitted with registry pins so that the pieces

First steps for the mold: it has pins, and the main parts have been carved on both faces. Next, using a partial cast, the filigree section needs to be carved on the back. Final decorations come after that.

always fit precisely. These are simple enough: drill through one side and into the other a bit with the pieces fitted exactly as you intend them to be. Widen the openings at each end of the drilled holes. Heat the mold, fit it together, and pour molten tin into the holes. Wipe off excess with a gloved hand and allow to cool. Why use tin? Well, although in period, pure lead was used, if there’s a problem with your mold, you may need to put the whole thing in the pot to melt out a locked casting. The pins will melt out, too, so unless you want another metal in your tin pot, you may as well use the same thing for every part.

Because the tin needs to be poured back out, the opening for the pour must be wider than usual, and the body of the hollow also is wider than a flat form would be, to ensure some liquid tin will be able to pour out. You’ll need to watch the temperature of your mold carefully: a hot

Test castings from the mold as shown above. Note the raw top edges.

mold won’t cool the tin quickly enough, and if you don’t wait, it may pour out half of your design with it. Of course, if you have really thin parts (like filigree, pin backs, etc), you’ll want your mold to be warmed up, or they won’t cast. It will take practice, but as with pewter, if it doesn’t come out, put it back in the pot and recycle it right away.

The open edge will vary depending on the type of item you are making. No matter where it is, you will want to clip off the excess once it cools. You can finish by filing or tumbling if desired. You don’t have tremendous control over thickness with this method; if you want the interior to be very smooth, you may need to do finishing work on it. If you want an exact thickness, you may as well use a wooden plug or other means to ensure that and cast with pewter. However, for odd-shaped pieces where a plug will not work, and for pieces that don’t need to be precise on the inside, this is an easy, medieval period method that works well. Happy casting!

From blank soapstone to finished tokens, this project took me a few days of actual work after several weeks of thinking, planning, and research. A few more days of work would have gotten the kinks out of the filigree, which (in a very period manner) refused to cast completely, but the event was coming soon, and the site tokens were well-received.

Cool Things I Learned About Pewter

I went a bit overboard on my documentation for a pewter piece I made recently, and learned some cool things I didn’t know. I’m sharing them here; it makes for a disjointed post, but hopefully it’ll be worth a read.

Backed pewter site tokens for the Palio event at Calafia-Gyldenholt Friendship Tourney, 2015

Backings: Small pieces of paper or parchment were used to back some badges. These materials degrade rapidly when exposed to moisture and weather, so all that is generally left for us to find today are the empty, folded-over clips, though one badge from Magdeburg retains its paper insert to this day. Other materials (contrasting metal foil, fabric or leather, for example) were used as well (Spencer, 5). Card stock is a perfect weight, and scrapbooking papers can make really pretty backings. I went a bit further, and painted mine with period paints. I got a great disco-inferno effect with thin brass foil repousseed in a simple diapered pattern of crossed lines, pushed in at the middle of each square.

Alloys: Spencer describes several alloys used commonly in the production of badges found in London, where many fine openwork badges have been found. Most were made using a lead-tin alloy. As tin was many times more costly than lead, cheaper pieces had higher lead content; however, if lead content is too high, casting problems result, including air pockets and a frosted, rather than shiny, appearance. The finest pieces were made of pure tin or a very high-tin alloy, as used in the production of Canterbury bells. The bells were cast in an alloy containing approximately 97% tin, 2% copper, and the rest bismuth and sometimes antimony, but no lead at all (Spencer, 11). The pewter I customarily use is fairly close to this alloy: 98% tin, 1.5% bismuth, and .5% copper (Rotometals). Coincidence? 😉

How thick is thick?  Like many others, I have heard from various sources in the SCA that period pewter was always cast as thin as possible. This makes sense from an economic standpoint (metal isn’t cheap). However, how thin was ‘as thin as possible’ ? I chose the Portable Antiquities Scheme database in the UK for a brief survey because it routinely includes data on thickness, rare in other sources. I did a broad search for medieval-period badges which had been published (and therefore verified as to authenticity and period) and created a table to get a rough estimate of customary thickness in a fairly random sample. I used only the first dozen pieces with a recorded thickness, not including pin backs, integral rivets, and the like, and skipped any ampullae, whistles, and other hollow forms to avoid confusion. Several of the thinnest finds are fragments, and might have had thicker cross-sections. The average thickness of my sample is 3.8 mm, with exactly 6 pieces below and 6 above this thickness. Finally, my archaeology degree pays off.

Finally, not new to me, but trust me, if you like period pewter, you need to visit the Kunera database.

Works Cited

Finds.org: Portable Antiquities Scheme. URL: https://finds.org.uk

Rotometals R98 pewter. URL http://www.rotometals.com/product-p/alloy_r-98_pewter.htm

Pilgrim Souvenirs and Secular Badges. Spencer, Brian. Woodbridge, UK. Boydell Press, in association with the Museum of London, 2010.

Adaptive Tools for a Pewterer

Among other things I do in the SCA, I am a pewterer. Pewtercasting in the Middle Ages was done in molds of stone or plaster, although less durable wooden and cuttlebone molds were used as well. Like many pewterers, I use soft, smooth-grained stone, like soapstone, for my molds, and carve them by hand. Like medieval pewterers, I use simple hand tools: a saw, hand-drill, and carving tools.

My dominant wrist has a ganglion cyst pressing on nerves and blood vessels, so ease of work is more than usually important to me. Holding narrow items, like needles and pencils, causes numbness and pain rapidly (within seconds), and soon after, loss of grip strength and control. A work injury to the shoulder on that side and the early stages of arthritis have taken a further toll on my ability to use hand tools. Many pewterers use dental tools as a convenient, relatively easy to get set of stoneworking tools; so did I, but these have become almost completely useless to me except as class tools when I teach. My ability to carve fine details in my molds was rapidly disappearing, and with it, my desire to make things.

Closeup, drilling center hole into the tool handle

I had to find a way to adapt my tools for use with my increasingly recalcitrant hand. I’d noticed that I could hold large tools (like ‘chunky’ screwdrivers) for much longer than small ones. If I could make big handles, I would be able to use fine tools. And of course, if I was going to make the handles, I might as well make the tools as well.

I visited my friend Roger Wells and made large birch-wood handles (turned on his lathe) which are easy for me to hold and work with. They also have a slight taper and flare at the base, allowing me to grip and control them with great precision. I also cut grip grooves in each handle (I made three), grouped so that each has its own numerical and nerdy pattern (integers, odd numbers, and the first four digits of pi, in case you were wondering). I put each handle in my bench vise and drilled the holes by hand, using an old-fashioned drill. I finished them by rubbing with bayberry wax… I know it’s not European, but I grew up in New England and love the stuff, and at least it isn’t polyurethane 🙂

Micro-blacksmithing setup; the forge is hiding behind my anvil on the left

For the next step, I needed to set up my micro-blacksmithing rig. I am not a Real Blacksmith ™, no matter what the t-shirt ads on Facebook say, but I do have a tiny, tiny forge that sits on top of a propane torch. I used this, a hammer, large pliers, and a small anvil, made from a length of rail. I didn’t end up needing the jeweler’s anvil, but added the end-nippers and a file, as well as fine sandpaper and a piece of granite counter. I’ll explain in a minute. There’s also a can of water, for cooling and hardening the tools.

Two of the tool ends are based on the shapes of the tools I used most often, each combining several tools in one. These two points have replaced a dozen or more tools, and I only rarely think I might need a different shape for most applications… and then, I turn one of them, and there’s the shape I needed, after all! I heated and hammered each of these into the rough shape I wanted, bending one to get an angle seen in many of the dental tools I frequently used. I then used the fine sandpaper on the granite as a flat sanding surface to sharpen the cutting edges. Finally, I reheated the tips to glowing, and dropped them into the water to cool and harden them.

The tips of my three mold-carving pewterer’s tools

The third (center in this shot) is a specific, purpose-built tool, in use in the header photo to do the one thing it does best: making dots with circles around them. To do that, it needed to have two points, one of which was close to the center of the tool as a whole, and the other, off-center slightly. I heated and hammered down the nail’s point, then flattened out the tip and cut just the very end of it slightly off-center, let it cool, and filed the gap a bit. The points were too far apart, though, for the size of dots-and-circles that I wanted, so I heated it again, and hammered the two points closer, very, very carefully. I should be clearer: I did not actually hammer the points at all. I hammered on the wide point below the points, making it fold together. I had to repeat the process about three times before it was the size I wanted. Then I heated and hardened this point, too.

Before setting the tips into the handles, I sawed grooves into the bases of the tips to give the epoxy something to hold onto. I put epoxy on the bases of the tips and pushed them into place, then let them set for 24 hours.

I really can’t say enough how much making these tools has changed for me. I thought I might never make another pewter thing I could feel good about. My depression was all too enthusiastic about jumping on that bandwagon. Instead, my very next project was one about which I am actually quite happy, and whose making will be the subject of another entry.

PS: The micro-forge is awesome, but I can’t find them for sale anymore. For people interested, here is an excellent site with a couple of DIY designs, safely made, and links to the materials you’ll need.

Backed pewter site tokens for the Palio event at Calafia-Gyldenholt Friendship Tourney, 2015