Brass Bar

This flat, oblong bar is made from brass, an alloy mixture of copper and zinc. Thanks to its attractive golden colour, brass has been a popular material choice for doorknobs, candlesticks, trinkets and buttons for centuries. The Romans were the first to master brass, and made it by a process called cementation, where copper, charcoal and a zinc ore called calamine were heated together with a crucible. Zinc’s boiling point is just 907°C, and so zinc vapour was released by the calamine which reacted with copper metal to produce brass. Nobody was really sure what was going on inside the crucible, and so the exact nature of brass remained a mystery for centuries; the alchemists hoped that its golden colour meant that it could be transmuted into gold. They were disappointed when, upon heating brass, it returned to copper. They described it as the ‘spirit’ (in other words, the zinc) escaping. Having eventually got to grips with zinc metal, the direct alloying of the two components of brass (a process called speltering), replaced cementation from the mid-19th Century.

 

Brass’ low melting point (900-940°C, depending on the exact composition) makes it popular for casting into moulds, and thin sheets of it are malleable enough to be cold-worked by hand tools. Brass also has low surface friction, so is popularly used in moving parts such as zips, locks, clocks and hinges. 

 

Brass is a sonorous material, meaning it supports the vibration of soundwaves. For this reason, it has been used to make blown brass instruments such as trumpets, trombones and French horns, as well as percussion instruments such as cymbals, gongs and bells. 

 

This material is not just a pretty face. Thanks to its high proportion of copper, brass is known to kill harmful pathogens on its surface within minutes to hours of contact, including E. coli, MRSA and Influenza. This so-called antimicrobial effect prevents frequently touched objects such as handles from becoming reservoirs of disease-causing pathogens, although how it does this is still not fully understood.