03 February 2014

Iron inclusions inside lead shot from the Mary Rose

The image above was published in Archaeology magazine last year.  It's a neutron-beam-generated image of a lead shot from the Mary Rose shipwreck, showing a fragment (?crystal) of iron inside the lead coating.  I found more details at The Telegraph:
Among the items most exciting archaeologists are cannonballs believed to be early examples of armour-piercing rounds. Such shells were thought to have been developed during the late 1800s, before the technology was refined during the world wars. But the new findings by experts working with the Mary Rose Trust, which has been preserving the ship, now suggest the technology was being used several centuries earlier — although it could also have been a money-saving strategy, using cheaper iron inside the lead balls.
Image credit: Bob Cywinski, University of Huddersfield.


  1. It looks like it would be a cube of iron. Part of a bar, possibly?

  2. Since lead is usually more expensive than iron, my guess is an early example of government contract fraud.

  3. I find it extremely frustrating I can never post to this site via Safari. Firefox seems to work. Perhaps it's some privacy filter, but I've white listed this site.

    perhaps this was a way to tune the kinetic energy? Once a bore size is set then the weight of a pure lead shot is fixed by the radius. But what happens if it turns out that more kinetic energy could be delivered by a lighter weight shot? you are stuck unless you have a way to adjust the weight. Adding iron to lower the weight could be a useful degree of freedom. That is to say, all else being equal two shots with the same muzel velocity, the heavier is better. But kinetic energy scales as the square of the velocity and only linearly with the mass. So if all is not equal and you can trade weight with muzzel velocity then a lighter shot might deliver more of the chemical energy release to the opponent. Moreover, if you are working at the extremes limits of the gun's peak wokring pressure then the light shot could allow more energy released at lower peak pressure.


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