Modern Alloys for Reproducing Ancient Bronzes
So you want to reproduce an ancient bronze artifact. To archaeologists, “bronze” is a copper-tin alloy (sometimes with small amounts of other elements) and “brass” is a copper-zinc alloy (sometimes with small amounts of other elements). Sheet metal suppliers use these terms differently. If you want to reproduce artefacts from before the invention of brass around Augustus’ day, you have a few options.
- You can work down cymbals and other thick objects from B8 bronze, a 92% Cu – 8% Sn alloy. Jeffrey Hildebrandt of Royal Oak Armoury in Canada shows how he made an Illyrian helmet from a cymbal. As of 2022, he is the only armourer I know who will accept commissions to make armour this way.
- C220 Commercial bronze is a kind of brass (90% Cu, 10% Zn). It looks somewhat like true bronze and is available in wide sheets in a variety of thicknesses (“gauges” in the USA and Canada). Different metals are measured in different gauges, and different shops measure the same thickness as different gauges, so when in doubt bring a pair of calipers!
- C510 Phosphor bronze is a true bronze with about 5% Sn. Its available in sheets up to 30 cm / 12″ wide. Since the beginning of the 21st century, many people in different countries have searched for any supplier of phosphor bronze sheet in wider widths, but none have found it. If you can buy several hundred or several thousand pounds, some foundries might cast it for you.
- Silicon bronze is a copper-silicon alloy. It does not seem to be useful for replicas of ancient bronze objects, but watch out for replica jewelry and belt mounts cast from it. These can look good until you try to peen them.
The composition of each of these alloys is defined and specifications are available on websites such as https://www.copper.org/resources/properties/144_8/ You can make greaves or multi-part helmets from phosphor bronze sheet, but to make a breastplate or a one-piece helmet you need to use commercial bronze sheet or work down a thick piece of copper-tin bronze.
Because I am not a coppersmith, I can’t comment on what some of these “false bronzes” are like to work. Armourers seem to have success with phosphor bronze, so-called commercial bronze, and B8 cymbal bronze.
Sheets of yellow brasses with more than 10% Zn are available, but don’t look or behave much like Iron Age bronzes. Sheets of pure copper are available, but look much redder than true bronze and are not as strong. The bronzes used for ancient arms and armour are about as strong and hard as medium-carbon steel which has not been heat-treated, so they were stronger and harder than most ancient steels. Whatever you choose, remember that metal dealers do not define “brass” and “bronze” the same way archaeologists do! But modern industries are very good at controlling the composition of cast metal, so if you get the alloy number and look up its composition, you can be sure of what you are buying.
Further Reading:
- “Potential bronze sheet …” Bronze Age Center 2008 https://www.tapatalk.com/groups/bronze_age_center/potential-bronze-sheet-t1789.html
- “Where do I get sheet bronze?,” Bronze Age Center 2010 https://www.tapatalk.com/groups/bronze_age_center/viewtopic.php?f=12&t=1869&p=13189
(created 27 April 2022)
