Secrets from the X-ray lab

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You may be surprised to hear that the British Museum has a cutting-edge X-ray imaging laboratory located four floors underneath the Museum. Using both traditional and innovative methods and equipment, scientists – including me – are able to answer questions that help with the interpretation and understanding of objects in the collection, including:

  • How old is it?
  • Where does it come from?
  • What is it made of?
  • How was it made?

Here are six such objects with secrets that X-ray technology has helped reveal.

Brass ewer

One of the star objects of the Albukhary Foundation Gallery of the Islamic world is this ewer (large jug) from Herat, modern-day Afghanistan, with beautiful birds surrounding the collar. With X-ray CT scanning (shown on the left above), we were able to determine how the birds were made. The X-rays can be very high in energy and are therefore very helpful for looking through metal objects such as this.

A photo of the top half of the brass ewer, shown in front of X-ray equipment.
On the right of this picture is the X-ray tube. The X-rays come out from just behind the brass square in the centre, pass through the ewer and make an image on a digital detector.

By rotating the ewer while taking images, we can see the inside from all angles, allowing us to make a full 3D picture (which you can find out more about in this Twitter thread). Since the ewer is 40cm tall, I scanned it in two halves, top and bottom, then stitched the two halves together to give the result in the first image.

An X-ray image of the top half of the ewer in black and white. The handle and birds around the rim are much whiter that the rest of the ewer. The silver decoration can be picked out on the sides.
X-ray image showing the changes in brightness that denote the different materials.

In the X-ray image above, we can see the silver inlaid design (it appears brighter because silver is denser than brass and so absorbs more X-rays) and various solder attachments. But what about the birds’ heads?

A video showing a cross-sectional view of the ewer.

To answer this question, we can go through the 3D picture of the ewer slice-by-slice – click to play the video above. On the right-hand side here, you can see that the bird head on the collar is a white outline, continuous with the body of the vessel (the handle is completely solid).

The birds’ heads, thought to be parakeets or pheasants, were made by hammering outwards from the inside of the vessel and were not made separately and stuck on, as originally thought! It is clear that incredible artistry and skill was needed to make this ewer.

A photograph of scientist Dan O'Flynn working at a computer screen in the X-ray lab. To the left, the door to the chamber is open and a ewer is seen under dramatic lighting.
Dan in the X-ray imaging lab, working with another ewer.
Cuneiform tablet

In the ancient Near East, clay tablets were inscribed with text called cuneiform, as well as clay envelopes to hold letters or important documents. With X-ray CT imaging, we were able to virtually strip back the clay envelope surrounding this cuneiform tablet, allowing us to read text that hasn’t been seen in over 4,000 years – without damaging the object!

The X-ray scans revealed the following text, translated by curator Jonathan Taylor:

2,427kg wool, as rations for the men of (the village) Gaka, under the supervision of the chief minister, via (Mr) Shesh-Utumu, from (Mr) Aradmu, governor of (the city) Girsu, have been withdrawn.

(Sealed with) the seal of (Mr) Babati.

Year Shu-Sin became king

By itself this information may seem insignificant, but it gives a valuable insight into the economic life of ancient Mesopotamia.

Tibetan thangka

This thangka (a painting on cloth) was featured in our recent major exhibition Tantra: enlightenment to revolution.

At the British Museum, we normally use X-ray imaging to look inside 3D objects, but it can also be effective on some more 2D objects including paintings and textiles. This Tibetan thangka depicts a Tantric teacher, or Mahasiddha (‘Great Accomplished One’) called Saraha, and was discussed in our blog about its conservation treatment here.

A photo of the front and back of the thangka. The front is brightly coloured and features strong patterns, and the central scene with six smaller figures and a larger figure in the centre. The back of the thangka is straw-coloured and features handprints in the centre, and the outline of a building.
The thangka after its conservation treatment, showing the colourful front side, as well as the reverse.

Conservation of the thangka was carried out in the Museum by conservators Alice Derham and Teresa Heady, and colour scientist Joanne Dyer to see if we could learn anything about the painting process.

Joanne identified paints containing gold, lead, mercury, iron and copper on the thangka. X-rays are good at detecting these heavy elements on carbon-based backgrounds – such as cotton or paper – so we hoped to be able to see them in an X-ray image.

The X-ray image below shows details of the Mahasiddha Saraha. A reworking of the gold lines radiating from the Mahasiddaha Saraha can be seen, as well as brushstrokes from the application of red paint.

A composite image showing the central figure of the thangka in a photograph at the top, and an X-ray at the bottom. The top image is brightly coloured and the below is black-and-white, revealing lines radiating out of the figure.
Detail from the visible image and X-Radiograph of the thangka. The latter shows two sets of gold lines radiating from the Mahasiddha Saraha.
Gandharan heads

In 2019, the Museum worked with Border Force to identify and return a number of heads of Buddhist sculptures from Afghanistan that were damaged by the Taliban and illegally trafficked to the UK (read more here).

A clay head of the female bodhisattva wearing a crown. There are traces of red paint on the face including the eyelids, the forehead and above the lips.
Moulded and painted clay head of a female bodhisattva wearing a diadem (crown).

CT scans revealed how the heads were made and scientific analysis showed that the red and yellow pigments found on the sculptures were made from common iron-rich ores.

An X-ray CT scan showing a cross-section of a clay head. The black-and-white image shows a solid white outline of the head and facial features, and the inside shows a rougher texture.
This X-ray CT scan shows a ‘slice’ through one of the heads, helping show how it was made with a two-layer technique.

An X-ray CT scan of the heads revealed a two-layered construction. Firstly, a coarse clay was used to roughly model the shape of the head. Afterwards, the face, hair and headdress were overlaid with a finer and more compact material which was then painted. The rediscovery of the sculptures was a good opportunity to conduct this work and we are very grateful to the National Museum of Afghanistan for permitting us to do so.

Three X-ray CT scan images showing the head of the female bodhissatva. The first image shows the head complete, the second shows a 'slice' taken on the right side of the face, revealing the internal texture. The third image shows a 'slice' taken in the middle of the face, also revealing the internal texture.
This X-ray CT scan shows the internal composition of one of the heads, and how this type of imaging can show the hidden cross-section of objects without damaging them.
Bronze age axe mould
Two halves of a bronze axe-head mould, heavily corroded.
This mould was used to cast bronze axe-heads, and is over 3,000 years old.

This copper alloy mould came to the X-ray lab through the Portable Antiquities Scheme, which registers finds of treasure in the UK. This fascinating object is a 3,000+ year old Bronze Age mould for making palstave axes from southern England. The X-rays revealed the extent of the partially visible cracks in the two halves, and corrosion (seen as small dark circles on the images).

3D models of the palstave axes made using moulds like this are available to view on Sketchfab here.

Two x-rays showing the axe-head moulds side-by-side. Large cracks are visible on the sides and centre of the moulds.
X-rays showed the full extent of cracks that were only partially visible with the naked eye.
Townley Discobolus
Scientist Dan O'Flynn working in front of three computer screens in the X-ray lab. To the left, the Discobolus statue can be seen in the chamber under dramatic lighting.
Dan in the X-ray lab with the Discobolus sculpture.

This marble sculpture shows an athlete stooping, about to throw a discus. It is one of several Roman copies made from a lost bronze original made in the 5th century BC.

X-ray images have revealed the multiple restorations conducted before the statue came to the Museum. The statue is famed for having a head that does not belong to the original body. The head is very close in age and style, and uses marble that is exceptionally well matched to the torso, but it has been attached at the wrong angle! Complete statues from the time reveal the head to be turned to look towards the discus, rather than the floor.

The images below show some of the other, less visible, restorations.

A composite picture showing the head of the discobolus statue looking to the left (image on the left), and to the right an X-ray of the same portion of the statue showing a join around the nose and a metal rod inside this area.
Here you can see the chin, mouth and nose have been reattached using metal rods for stabilisation.
A composite image showing two views of the left hand of the Discobolus sculpture. On the left, a photograph, and on the right an X-ray showing how the index finger has been joined on using a metal rod inside.
And the left index finger of the statue is actually a modern restoration (made of resin), of which we have a record. You can see a rod has also been used here.

We hoped you enjoyed this brief introduction to X-ray imaging at the Museum. You can read more about scientific research in our blog celebrating 100 years of science at the Museum here.

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