We work very closely with archaeological scientists here in the British Museum.
And one of my colleagues, Dr Aude Mongiatti, has been working on the Oxus treasure,
which is a collection of about 180 gold, silver, and gilt-silver
objects that date from the fifth or fourth century BC.
Hi my name is Aude Mongiatti
and I'm a scientist here at the British Museum. I specialise in ancient metallurgy.
And today I am studying some gold objects from the Oxus treasure.
This is an example you have here a gold roundel with boars and ibex on it.
And what I'm interested in is understanding how it was made and also its composition.
So I am using the scanning electron microscope, variable pressure scanning
electron microscope which allows us to study objects non-destructively and to
analyse them as well.
Here I will now push the door, we can know the position
of the object at all times thanks to the infrared camera within the chamber.
And so it's actually ready now so I'm able to switch on the high voltage so
the incident beam of electrons onto the object to create an image. It should now
be able, yes there it is. We have got a first image of our object.
Then we get to a small area and we get the image in focus as much as we can, we go higher in magnification.
And then we can move on the surface of the object.
This is an ear of one of the of the boars.
Those long grooves are part of its mane.
And this is the mane going through here. And what we are trying to look at is the type of
tool marks that we can see on the images. And here for example we can see cuts
which have been done in the mane but the tool has actually gone further down.
They're quite sharp angled. Other grooves I think the ones which we can see on the
ear they're much smoother and so the tool that has been used
is most probably with a blunt edge and it has been gently pushed into the
surface of the metal to create the groove instead of cutting through the
metal to do that. So this is the sort of features we're trying to look for in
order to identify manufacturing techniques on objects.
If I show you one of these gold armlets this is a typical example of a cast. The casting method
used is a well known method for the period which is lost wax casting. Some of
the decoration has been added post casting using techniques such as chasing
and punching which is using a blunt edged tool to create the various grooves and patterns.
Here is another object illustrating a different type of technique.
It will have started with a little cast ingot of gold but in order
to create this roundel, make the shape and then decorate it it's only hand
working which has been involved. Again chasing and punching, gently hammered
from the back and from the front as well.
So the scanning electron microscope as I've shown allows us to capture high
resolution images but it also allows us to analyse compositions.
The SEM is equipped with a detector for energy dispersive x-ray spectroscopy which
allows for chemical characterisation of a sample or an object. So this detector
allows us to acquire spectra typical of the chemical composition of a sample or object.
So in order to analyse, in our case we're looking at gold alloys, we
first acquire an image of the area we are interested in. And this is relatively
you know low magnification it's 200 times you can go much higher if you're
interested in a single crystal or phase as we call that in a metal.
So once we have acquired the image of the area of interest we can choose to analyse a
whole area — this whole area inside the yellow
square is being analysed — but I can also choose to do spot analysis.
So I've done four little spot analyses here. Then you want to have an idea of the chemical
composition overall but also each phase. And so while the spectrum is being
acquired you can watch it live and see the elements which are being detected.
What we see here is the composition of the surface of the object.
And in our case we can see that there is a lot of gold with some silver and copper.
What has to be borne in mind though is that due to various factors such as
burial environment and/or surface treatment applied by the goldsmiths,
some of the alloying elements copper and possibly silver may have been removed
from the surface. So it may be that in the actual core of the object the silver
and copper contents are higher than what we detect here on the surface.
So yes this is the final spectrum that you get upon doing chemical analysis. And then
the software also allows you to quantify. So here I have chosen to highlight gold,
silver, and copper which are the alloying elements for this alloy and I can see
that on my surface on this particular object and on this particular area there
is about 90% gold, about 9% silver and very little copper.
So we get two types of results, the spectrum where we can actually check whether the
elements that the software detects are really there and then the quantified and
normalised results.
What I found interesting is the variety of alloys which have been identified.
For example this particular roundel which
looks a lot greener than the other gold objects due to its high silver content
it has got about 20%, it shows that it's an unrefined gold used for this particular object.
We were really excited right from the outset to
put the results of archaeological science in the interpretation of this
exhibition. One of the most interesting things about this new research was the
real proof of the level of skill and the variety of techniques used by the
different craftsmen to make these different objects.