Ancient Bronze is a copper-based alloy with anywhere from 10-12.5% tin. It was widespread by the 2nd Millennium BC and depending on the country it was found in, its composition varied.
In the Bronze age (4000 BC to 2000 BC) Bronze was usually an alloy of Copper and Arsenic, or with added Aluminium and Manganese. Arsenic was common in Bronze at the time because it acted as a deoxidizer and produced arsenic oxide fumes that that boiled out of the melt, taking the oxygen with it. Arsenic also occurred naturally in the copper ores that were mined.
Arsenic based Bronze also allows work hardening as compared to pure copper, so it’s a better material to work with – especially considering the tools that people had 4000-6000 years ago!
There are a few reasons that civilizations smelted Bronze:
- It’s relatively low melting point of about 950 °C (1742f), as compared to iron at 1,538 °C allowed the current pottery kilns of the age to handle the melting point of Bronze.
- Bronze is harder and more durable than metal objects that ancient civilizations used, especially more so than copper which was widely used for tools and weapons.
- Tin and Copper ore discoveries and trade access made the alloy a suitable choice. Tin is also very easy to work with and has a low melting point at 231.9°C, however tin mines were rare in the Bronze age.
Types of Bronzes
Today there are many different types of Bronze alloys. Copper is the base metal, but the alloying metal can be different depending on the end use of the bronze. Some example of modern Bronzes:
- Tin Bronze – the ancient Bronze recipe. Density of 8.78 g/cm³.
- 87.5% Copper
- 12.5% Tin.
- Manganese Bronze – Density of 7.7 g/cm³. Very strong and high corrosion resistance.
- 60-68% Copper
- 25% Zinc
- 3-7.5% Aluminium
- 2.5-5% Manganese
- 2-4% Iron
- 0.2% Tin
- Aluminium Bronze – Many variations of this recipe. Useful in marine applications. Has a biostatic effect which prevents colonisation by marine organisms such as Algae. Density of 7.21 g/cm³.
- 88-94% Copper
- 4-6.5% Aluminium
- Up to 1% Iron/Nickel/Manganese/Zinc
- Silicon Bronze – Noted for its easy pouring characteristic. Common in modern Bronze product offerings. Density of 8.91 g/cm³.
- Up to 92.6% Copper
- 2.8-3.8% Silicon
- Up to 0.8% Iron.
- Up to 1.5% Zinc
- 0.5-1.3% Manganese
The cost of Tin Bronze
For small scale production the cost depends on:
- Copper and Tin prices.
- Furnace and tools
- Time
If I wanted to produce a 100kg Bronze Ingot today it would be based on an 87.5 & 12.5% mix of the two metals below. This would bring the cost to $1,357 USD. You could consider cheaper prices from scrap sources, although there are costs involved in sourcing those prices which commonly don’t get included in a finished products price.
- The Copper price in 2021 is currently $10,724 per tonne, or $10.72 kg and 4.87 lb. In Australian Dollars this is $13,689 per tonne, $13.69 a kilo.
- The Tin price in 2021 is currently $33,562 per tonne, or $33.56 kg and $15.25 lb. In Australian Dollars this is $42,840 per tonne, $42.84 a kilo.
From here there are depreciation costs (wear and tear) on the furnace and crucible primarily, plus all of the associated tools that are required to melt Bronze. Fuel and PPE are other consumables that need to be included in the final production cost. Lastly there is the time taken to melt and fabricate a finished ingot. All of this goes a long way into the price paid above spot rates for smaller ingots and products, and especially so for specific alloys such as Ancient Bronze or Nordic Gold for example.
Bronze is a great looking alloy and one of my personal favorites as it just has a unique color, one that I can’t quiet figure out.
Anyway, here are some fun facts about Bronze which may come in handy as good pub trivia down the track!
Bronze Trivia
- Bronze is not magnetic.
- The first alloy used by humans (that we know of)
- Was replaced by the iron age.
- The word Bronze comes from Italian origins in the 13th century from the word Bronzo, meaning ‘bell metal or brass’.
- The oldest Bronze found dates back to Serbia from 4500BC.
- Before Bronze there was…..well, stone!
As our business grows we will be adding in Bronze ingots and coins for sale as a specialty product. Hopefully we can get to this soon, so be sure to check them out when they arrive :)
GWB Team.