What are metal alloys?

The Today programme on BBC Radio 4 this morning reported on the discovery (in 2005) of a buried youth near Stonehenge in southwest England whose remains are thought to date from around 3550 years ago. The youth was buried with a necklace made from 90 or so small amber beads and this hints at his possible status and is being discussed at a meeting to celebrate the 175th anniversary of the British Geological Survey.

The researchers interviewed about the finding alluded to a vast trade network that may have existed at the time and suggested that the youth was of high status. (The trade link and the amber beads suggest to me that the youth was a market trader from the Mediterranean region (based on chemical fingerprinting of his teeth) rather than a dignitary though).

Anyway, one of the materials the interviewees referred to several times was tin, although the interviewer did not ask about what tin was so important at the time. I suspect that he didn’t really see the relevance and I also suspect that the majority of the listening audience would not see the relevance of tin either.

Of course, 3550 years ago was the height of the so-called Bronze Age. And, the “Boy with the Amber Necklace”, was unearthed next to a Bronze Age burial mound during roadworks for military housing. The mound is about 5km south-east of Stonehenge on Boscombe Down.

Bronze is an alloy of two metals: mainly copper and a little tin. The tin toughened up the flexible copper allowing bronze to be used in weapons, armor, building materials, and decorative objects where copper would be too weak.

There are many different bronze alloys but bronze is typically 88% copper and 12% tin. Alpha bronze consists of a solution of tin in copper (a solid, but a solution nevertheless) and is used to make coins, springs, turbines and blades. Today, commercial bronze is 90% copper and 10% zinc. Architectural bronze (57% Copper, 3% Lead, 40% Zinc) is actually a type of brass alloy (brass is copper and zinc).

So the relevance of mentioning tin in the news report is that it was the crucial additive for the Bronze Age, without it we wouldn’t have come of Age. But, perhaps it was too much chemistry for the BBC to cope with at 7am…

2 Comments.

  1. Alan Crooks

    Wish I’d heard this programme :-(

  2. David Bradley

    Listen Again – http://news.bbc.co.uk/1/hi/help/3681938.stm

    This morning’s program interviewed science writer Joel Levy and Rosie Franklyn’s PhD student from the DNA days Raymond Gosling. Fascinating stuff, but unfortunately they had to cut them short for the weather forecast – http://en.wikipedia.org/wiki/Raymond_Gosling

    It’ll be on listen again on Friday…