Choosing Which Metal To Use

I often hear conflicting complaints from historic re-enactors and SCA folks alike:  “the problem with my group is too many authenticity Nazis” and “why can’t people at least make a more accurate attempt at their clothes?”

As a professional jeweler and merchant at SCA events, I frequently wrestle with the disparity of these sentiments. Some of the choices are difficult, but some are easy from my perspective. I make many of my items using a copper alloy known as bronze. Some merchants choose any old copper alloy without regard to what would have been used historically. But using true bronze gives my pieces the look and feel of the originals that they are patterned after.

Bronze was used to make weapons, armor, knives, brooches, hooks, crosses, and many, many, other items. It’s a ubiquitous material throughout Medieval history, and much earlier. Bronze is a remarkable alloy with multiple formulations. The first bronze included copper and arsenic (yes arsenic). Fortunately for real sticklers for accuracy, arsenic bronze was largely replaced by a tin and copper formulation that we recognize today as true bronze. A bit of good news for authenticity fans – true bronze became the primary bronze from the 3rd millennium BC.

There are very few places on the earth where copper and tin are found together (one site each in Thailand and Iran), so true bronze is reliant on trade. Great Britain was the major source of tin in Europe, which can explain some of the unusual trade goods found in Britain.

Copper alloys are truly remarkable. They can be harder than wrought iron, be sharpened for cutting edges, and the alloying process is comparatively easy. Depending on the alloy (tin, zinc, lead, silver and other additives) the metal can take on many different hues. Each formulation has unique characteristics, and in our modern society they have very specific names – brass, yellow brass, and nickel silver, to name a few. Some alloys are malleable, others are hard and brittle, and still others have differing degrees of chemical resistance.

Are there any other practical reasons for me to want to use true bronze instead of some other bronze alloy? Yes. True bronze can be enameled. Now some of the other alloys can be enameled, too. But the problems with enamels changing color because of the zinc in brass, for example, can be difficult to overcome. True enamel is a form of ground glass that is melted and fused to the metal. If you are interested in more detail about enamel and enameling, just visit my enamel blog.

Handled ewer. Copper alloy with champlevé enam...

Handled ewer. Copper alloy with champlevé enamel, Late Roman work. (Photo credit: Wikipedia)
















Today we know that iron replaced bronze for knives, weapons, and many other larger items, as iron working skills matured. Iron could maintain a sharp edge longer, withstand greater bending forces, and eventually could be made into steel. The transition to iron seems to have been encouraged along by a tin shortage. Around 1200 BC the shipment of tin around the Mediterranean plummeted – coincident with population migration. There’s no definitive proof of the link between migration and the tin shortage, but some archaeologists believe that there is a causal relationship between the two.

But are there any other metal choices that we need to make for period reproductions? We’ll talk about that next time.

The Way That I Cast: Lost Wax Process Part 5

Last time we ran through the basics of the end of my lost wax casting process. But I often get questions about how I got started casting, and how other people could get started, too.

Well, like many people who hang around with reenactment groups, I had seen pewter casting, and took a basic class on carving soapstone molds and pewter casting. It was fun and I wanted to learn more about casting.

Only an hour drive from my house there was a community college with a jewelry department. They taught all day classes on Friday – 8 AM to 5PM. One of my girlfriends suggested that we take a Friday class together. So I went back to college. The classes were different every semester, and included casting, enamelwork, and metal forming. We had about three hours of lecture time and then the rest of the day was hands-on. Best of all we had access to all of the equipment that the jewelry lab had: kilns, centrifugal casting machines, torches, hydraulic presses, you name it. They didn’t care what sort of items we made, just that we were learning to do the semester’s processes.

I loved it. I took classes for a couple of years, and started collecting equipment to be able to do my own casting. I started casting using casting sand, instead of lost wax. It required a LOT less equipment.

Equipment is the big barrier for most beginning jewelers. My current set-up, if I had to buy it new, would be worth about $10,000, and that isn’t even counting the small tools and a lot of the expendable supplies. More basic set-ups are certainly possible. As I mentioned, I started my home casting projects using casting sand. This eliminated the need for almost all of the wax equipment, the mold making equipment, the flasks, the de-waxing and burnout ovens, the vacuum machine and the vacuum caster. The minute that you decide that you want to do lost wax casting there are a lot of expenses that can’t be avoided.

Equipment can be purchased used. I have actually purchased a lot of my equipment used through Rio Grande Jewelry supply. My basic bench and some of my hand tools were bought used from a jewelry company that was shutting down.

The most basic kit that I can think of, that would allow successful lost wax casting would require: a wax model, a flask large enough for the model, a base for the flask, investment to create the mold in the flask, a vacuum machine for removing the bubbles from the investment in the flask, a kiln to melt out the wax and harden the investment into a useable mold, a torch to melt the metal for the casting, a crucible to melt the metal in, and a centrifugal casting machine. Here is a picture of my centrifugal caster.

centrifugal caster

It literally, at the flip of a switch, flings the molten metal into the flask using centrifugal force. The biggest problem with the process that I just mentioned? You destroy your model. If the casting fails you have to create a new model.

Next time: More About Lost Wax Casting Options

The Way That I Cast: Lost Wax Process Part 4

Last time we created the actual molds that are used for casting, and we poured the molten metal into them. But what happens now? Well, they need to be quenched.

Quenched? Yes. The metal needs to be cooled down the rest of the way so that it can be handled, and it needs to be removed from the plaster in the flask. Quenching accomplishes both of these things at the same time. Here is a picture of my high tech quenching arrangement. I have a bucket of water sitting up on a metal stool. The still hot flask (in the tongs) is lowered into the bucket of water. Sizzle, spit, steam and it all happens. The forceps in my other hand are used to remove the still warm metal from the flask. I set it aside into another smaller container of water while I clean the flask.

quench and reveal

There is always some plaster left in the flask, so I scrape it out with a putty knife and throw it into the other bucket that you can see next to me on the floor. The flask is then scrubbed with a wire brush, rinsed and put on the floor to dry.

flasks drying

And here they are drying! Meanwhile the newly cast piece is sitting in a small container (an old cooking pot) full of water. It is now cool to the touch, and this is what a typical one looks like.

newly cast buttons

Once I am done casting it is time to begin making these messy looking blobs into something worthy of being put in my shop. This picture shows the basic process. First the pieces, in this case buttons, are cut off of their sprues. This process often requires that the metal has to be cut apart in stages so that none of the buttons are damaged. Then the sprues are set aside to be cleaned and the buttons are given an initial tumble to remove any remaining investment and reveal any surface imperfections. Any flawed buttons go into the sprue pile to be recycled later. The remaining buttons are sanded, polished, inspected, and touched up until they look like this.

smaller button picture

The sprues are then cleaned and polished to remove all traces of investment and metal oxides. They are then dried and put away for later use.

I thought it was important to include a lovely picture of me in all of my pouring safety gear. Quite the fashion statement!

full kit

So for those wishing to replicate this major fashion statement…Starting at the top we have a full face shield to prevent burns from splashing molten metal and boiling water. Under that shield we have a high quality particle dust mask. The process of quenching the flasks can put quite a bit of fine particulate silicon into the air, which is very bad for your lungs. The blue jacket with leather sleeves is a welding jacket – doesn’t catch on fire easily and protects from an assortment of hot things. Leather welding apron and gloves complete the ensemble. What you can’t see is loose fit cotton jeans and high top leather boots.

Next time: How I Got Started Casting