Materials Science for Cosplay 2: Copper and its Alloys
Steampunks and other cosplayers spend a lot of time in the company of copper and its alloys, brass and bronze. Here I hope to throw a little of the science of the stuff your way to make it easier and more rewarding to work with.
Copper was one of the first metals to ever be used by humans. Chunks of it could be found in a workable state lying about on the surface, requiring no mining or smelting to extract it, much like the early sources of gold. It also melts at a relatively low temperature and mixes well with tin and lead. This allowed it to be the material that both the copper and bronze ages were named for. Now, we have to mine it, but only the most hardcore cosplayers will bother with that, so let’s move on.
Copper is a base element, 29 on the periodic table, which makes it just a bit heavier than steel by volume. It’s only about one quarter as strong as common mild-steel. To a costumer, though, that’s generally an advantage as you can bend it to your will more easily, often without having to worry about heating it up to make bends.
It is more conductive than steel, both thermally and electrically. It’s also very ductile (can be stretched out like taffy) without being overly soft or toxic, like lead. This makes it terribly useful for things like making pipe and wire.
Its usefulness, unfortunately, leads to the main problem with copper: It’s kind of pricey. Copper is not terribly abundant, like aluminum or iron, so the demand somewhat outstrips the supply sometimes and it can be hard to get in convenient shapes and sizes at a reasonable price. The most likely form you’ll find it in is as copper pipes at the hardware stores or in cables.
There are two classes of common copper alloys, brass and bronze. Brass is a mix of copper and zinc, usually in the 55%-80% copper range. The stuff I like to work with the most is called cartridge brass. As the name suggest, it’s used in bullet cartridges. It’s a 70-30 mix and it has great cold-working properties that allow me to make armor and sheet metal accessories from it.
Bronze is a bit more complicated. Historically, bronze usually refers to a blend of copper and tin. In has come to refer to variety of copper alloys including alloying elements such as aluminum, silicon, and (confusingly) zinc.
Their properties can vary widely based on their alloys. Broadly speaking, though, bronze is good for casting, brass is good for cold working (stamping, bending, etc)
A note, if you are going to do any casting, be very careful with your alloys. You need very good temperature control to melt anything with zinc in it as it will start to evaporate and the vapors are somewhat toxic.
The value of copper in electronics leads to a lovely side-effect. A couple of fairly nasty chemicals that might be otherwise difficult to find are available at most electronics supply stores. Ferric Chloride, Ammonium Persulphate, and a HydroChloric Acid/Hydrogen Peroxide mix can all be used to etch copper as well as most brasses and bronzes. What is even nicer about this is that both electrical tape and sharpie ink can work as a mask for etching.
As you work metal cold by bending and shaping it, it gets stiff and brittle. This is called work hardening. It is possible to reverse this process with the careful application of heat. This is called annealing the metal.
Copper and brass are pretty easy to anneal. In short: Make it really hot and then dunk it in cold water. This is nice as it’s a very fast process and you can do it with a butane torch.
Heat the metal just until it starts to glow red. Alternately, scribble sharpie over your piece and heat it until it’s gone. Quench it in cold water while it’s still hot and you’ll get a nice soft metal to work with again. Overheating copper isn’t really a problem. Overheating brass, however, has the zinc fume problem, but also oxides can form that will mess up the properties of the metal.