A few questions about bronze

January 25, 2014 3:02 PM

What is the functional difference between arsenic bronze and tin bronze? Do the two alloys have different properties, aside from one is toxic to make? I keep reading that the best bronze is 10% tin, but you can make bronze with 2% tin or arsenic. How big a difference is there? Pewter is 90+% tin, with copper and antimony (and sometimes lead). Any reason you couldn't make bronze out of copper + pewter?
posted by musofire to Science & Nature (4 answers total)

Bronze was made out of copper and arsenic to form arsenic bronze. It was only later that tin was used, becoming the sole type of bronze in the late 3rd millennium BC. Tin bronze was superior over arsenic bronze in that the alloying process itself could more easily be controlled (as tin was available as a metal) and the alloy was stronger and easier to cast. Also, unlike arsenic, tin is not toxic.
posted by vulnus at 3:28 PM on January 25, 2014

Bronze is pretty much defined by "copper + tin", but there are a LOTS of different alloys. For example, aluminum is used in one type, makes it a bear to machine.
What you describe above is pretty close to 932 bearing bronze. , but be forewarned, even minor trace amounts of certain other metals can really foul up the properties of what you are trying to make, so the antimony might be a dealbreaker.
posted by rudd135 at 8:59 PM on January 25, 2014

It's been a long time since I studied this (and I was never a specialist, I was just interested). Generally speaking, any two alloys will have different properties, and in addition to the properties granted by the materials present in the alloy, the smelting conditions have an effect, as does any treatment done afterwards (cold working, hot working). Off the top of my head I remember very little about this - along the lines of 'lead makes casting easier' - but probably at a cost in brittleness or similar later, but I don't remember - and for different alloys, cold working can strengthen the material or cause brittleness, that sort of thing.

A few reading recommendations for you -

Early Arsenical Bronzes--A Metallurgical View - first page preview in JSTOR but possibly the full article would be accessible from your local or university library.

Likewise Arsenic Bronze: Dirty Copper or Chosen Alloy? A View from the Americas.

This one is open access - Copper Alloys - Early Applications and Current Performance - Enhancing Processes. Chapter 1 looks most applicable but other chapters might also be of use.

Copper and Copper Alloys - a few pages that might be relevant on a Google Books preview.

Metallography and Microstructure of Ancient and Historic Metals - a PDF of David Scott's book available for download from Getty.

Regarding making bronze from copper and pewter - a) if you're googling, 'copper alloy' might be a more useful search term, and b) yeah, people have been re-melting and repurposing various objects into various other objects since ever - it's possible, but risky if you don't know what you're doing or what exactly is in what you're working with, in the sense that you won't be sure what the properties of the final product will be - it might corrode quickly or be brittle or in some other way not do what you want it to do. A sort of overview of this sort of re-working objects for their raw materials is From Bells to Cannon – The Beginnings of Archaeological Chemistry in the Eighteenth Century - another landing page for an article behind a paywall, but again, your local or university library might have access to this.

This was a lot of words for not a very useful answer, sorry! If you're interested in any of the journal articles, I can help out with PDFs if you memail me.

I've tested the links but I'm still nervous about some of them - let me know if they don't work.
posted by you must supply a verb at 4:02 AM on January 26, 2014

>tin is not toxic.

Tin is less toxic than arsenic (by a lot), but it's by no means not toxic.
posted by kjs3 at 5:15 PM on January 26, 2014