Research news

Study of two large crystal skulls in the collections of the British Museum and the Smithsonian Institution

British Museum skull

The British Museum crystal skull

The life-size carving of a human skull in the British Museum collection was made from a single block of quartz crystal (a clear colourless variety of quartz known as rock crystal). According to Museum records, the skull was acquired in 1897 from Tiffany and Co., New York, through Mr George Frederick Kunz.

In one of his numerous publications, Kunz claims that the skull was brought from Mexico by a Spanish officer before the French occupation (1. See references at the bottom of the page). It was sold to an English collector and acquired at his death by Eugène Boban, a French antiquities dealer, later becoming the property of Tiffany and Co.

At that time human skulls and skull imagery were known to have featured in Aztec art and iconography in Mexico when first contact with the Spanish was made in AD 1519. They were worked by Aztec, Mixtec and even Maya lapidaries, and a human skull covered with turquoise and lignite mosaic is displayed in Room 27: Mexico of the British Museum catalogue entry, 1898British Museum (2).

They were also carved in relief in basalt or limestone as architectural elements, as can be seen in a large shield-shaped stone relief discovered at the Aztec Templo Mayor in what is now Mexico City.

However, the authenticity of skulls made of quartz crystal soon came to be questioned. Although some are said to be examples of colonial Mexican art for use in churches, perhaps as bases for crucifixes, they may be among the large quantities of forgeries produced during the second half of the nineteenth century, when interest in collecting ancient artefacts from Mexico was at its height in both the United States and Europe. Some of these pieces made their way into museum and private collections. 

Staff in the Department of Scientific Research at the British Museum examined the British Museum skull several times between 1950 and 1990 (3). Observations made with a binocular microscope suggested that the techniques of carving were probably atypical of pre-Columbian times. Also, the large piece of rock crystal used for the skull was thought to have come from Brazil, an area far outside the ancient trade network of Mexico.

Smithsonian Skull

An increasing number of large and small quartz skulls have become known, particularly in recent Skull from the Smithsonian Institutiondecades. None has ever been reported from well-documented official archaeological excavations.

In 1992, almost a century after the crystal skull was acquired by the British Museum, a particularly large white (or milky) quartz skull with a hollow cranium (right) was sent anonymously to the Smithsonian Institution, Washington D.C. An accompanying note said the object was bought in Mexico City in 1960. The carving, like the British Museum skull, is stylistically somewhat anomalous when compared with ancient Mesoamerican depictions. For example on both skulls, the rigid linearity of features representing teeth contrasts with the more precise execution of teeth on pre-Columbian artefacts. 

The arrival of the white quartz skull led to a study of archival documents concerned with the early history and acquisition of several crystal skulls in museum collections. It became apparent that not only had the dealer, Eugène Boban, owned the British Museum skull (as alluded to above), he had previously also been involved in the sale of three other rock crystal skulls, one which is around 11 cm high and two small ones (which are less than five cm high), currently in the Musée du Quai Branly, Paris (4,5,6,7).

Collaborative study

Margaret Sax examining the British Museum crystal skull

In 1996, a collaborative programme of authenticity studies was set up between the British Museum, the Smithsonian Institution and the Department of Earth Sciences and Geography at Kingston University, Surrey.

Small skulls carved from rock crystal have perhaps attracted less public attention than larger examples, and the investigations were focused on the origin of the large skulls in the two national museums. Because stone objects cannot be dated satisfactorily by the techniques available today, the aim of the project was to answer three questions. How were the skulls carved? Where did the large pieces of quartz originate from? What is known about the early history oCrystal Mixtec gobletf the skulls?

A number of other rock crystal artefacts of undisputed origin are also known, including beads and zoomorphic figures. The opportunity was taken to compare the two large skulls to several other rock crystal objects from well-documented excavations in Mexico City and Oaxaca, Mexico, including the goblet shown here, which is 8.8 cm tall and is the largest documented rock crystal artefact to have been excavated at a pre-Columbian site and is now in the collection of the Museo de las Culturas de Oaxaca.

An approach developed early in the 1990s in the British Museum for investigating carving methods was adopted for the study of skulls. This enables the use of tools and techniques to bScanning electron microscopee identified from the fine detail of the carved features or ‘tool marks’ preserved on hard stone objects (8). In the investigation of the skulls, the faint tool marks remaining on the highly polished surface of the British Museum skull and the pitted matt surface of the Smithsonian skull were examined under a microscope. Moulds were also made of these tool marks using special silicone dental ‘wax’ and these were examined at high magnification in a scanning electron microscope (SEM). 

The tool marks on the skulls were compared to the tool marks remaining on genuine pre-Colombian rock crystal objects. The regular characteristics seen on both skulls showed they Detail of the teeth of the British Museum skull. A mould made of the teeth is shown in the image to the rightwere mainly worked with rotary wheels in conjunction with very hard abrasives. In the SEM image shown below, the curvature along the moulded teeth shows they were cut using a wheel.

SEM image of a mould from the carved mouth and teeth

The characteristics contrasted with those seen on pre-Columbian pieces, which were carved with hand-held tools, as can be seen on the Aztec Codex Mendoza in the collection of the Bodleian Library, Oxford.

SEM image of the moulded details of the internal surface of the goblet

SEM image showing regular striations retained in the polish at the side of the skull

Rotary cutting wheels were not introduced to the Americas until after the Spanish conquest of Mexico in 1521. The skulls therefore cannot be of Aztec manufacture. The white quartz material of the Smithsonian skull is of relatively common occurrence, but the large clear quartz crystal used for the British Museum skull would have been obtained from a special source. Raman spectroscopy (below, left) was used to confirm that the skull was carved from rock crystal.

Raman spectrometer being used to study the skull

The upper trace shows the spectrum obtained from the British Museum skull, the lower trace is obtained from a reference sample of rock crystal

Because the characteristics of inclusions in clear quartz may indicate the geological conditions under which the original crystal formed (9,10), the mineral composition and the fine detail of the inclusions in the clear crystal of the British Museum skull were investigated to provide information on the provenance of the source.

To address the history of the British Museum skull, archival research has aThe skull being examined under a binocular microscopelso been carried out. These results and those of the technical studies of the two skulls have just been published online by the Journal of Archaeological Science in a paper describing the origins of these two large carvings: ‘The origin of two purportedly pre-Columbian Mexican crystal skulls’, Journal of Archaeological Science (2008) by M. Sax, J.M. Walsh, I.C. Freestone, A.H. Rankin and N.D. Meeks.

Whatever their origin, the spectacular appearance of crystal skulls continues to fascinate as much as when they first appeared during the second half of the nineteenth century.

This interest continues today - the new film Indiana Jones and the Kingdom of the Crystal Skull explores other avenues of their story.

Margaret Sax (British Museum), Jane M. Walsh (Smithsonian Institution), Ian C. Freestone (Cardiff University), Andrew H. Rankin (Kingston University) and Nigel D. Meeks (British Museum)

References

1. Kunz, G.F., Gems and Precious Stones of North America. New York, pp. 285-286, 1890.

2. McEwan, C., Middleton, A.P., Cartwright, C. and Stacey, R., Turquoise Mosaics from Mexico.  London, British Museum Press, 2006.

3. Jones M., “The Limits of Expertise”, in: Fake? The Art of Deception. London, British Museum Publications, pp. 296-297, 1990.

4. Walsh, J.M., “Crystal skulls and other problems”, in: Exhibiting Dilemmas: Issues of Representation at the Smithsonian, A. Henderson and A.L. Kaeppler (eds.). Washington and London, Smithsonian Institution Press, pp. 116-139, 1997.

5. Walsh, J.M., “Falsificando la historia, los falsos objetos prehispánicos”, Archaeologia Mexicana Vol XIV(82), 2006.

6. Walsh, J.M., “Legends of the crystal skull. Why Indiana Jones might want to rethink his latest quest” Archaeology Magazine, May/June 2008

7. Smith, D., ‘With a high-tech microscope, scientist exposes hoax of 'ancient' crystal skulls’, Inside Smithsonian Research, Quarterly Newsletter on Science, History and the Arts, No. 9, Summer 2005

8. Sax, M., N.D. Meeks, and D. Collon., “The introduction of the lapidary engraving wheel in Mesopotamia”, Antiquity 74(284), pp. 380-387, 2000.

9. Rankin, A.H., “Fluid inclusions; a new look at ancient fluids in crystals”. Geology Today Vol 5, pp. 21-24, 1989.

10. Rankin, A.H., “Fluid inclusions – tools for geological investigations”, in: Encyclopaedia of Geology, R.C Selley, R. Cocks and I. Plimer (eds.). Elsevier Science, Chapter 9, pp. 253-260, 2005.


Images (from top, left to right):

  • The British Museum crystal skull
  • The British Museum catalogue entry made in 1898 that records the acquisition of the skull
  • White quartz skull with hollow cranium, # 409954 Natural History Museum, Smithsonian Institute. Photograph courtesy of James Di Loreto and Donald Hurlburt/Smithsonian Institution
  • Margaret Sax of the British Museum examining the crystal skull under a stereomicroscope. Photograph courtesy of Ana Garcia
  • Rock crystal skull goblet with cup-shaped hollow base, 10.105605 Museo de las Culturas de Oaxaca, Mixtec culture, around AD 1200-1521
  • Scanning electron microscope (Hitachi S3700) in the laboratories of the Department of Conservation and Scientific Research, British Museum. Photograph courtesy of Laura Jones
  • Detail of the teeth of the British Museum crystal skull
  • SEM image of a mould from the carved mouth and teeth - the curvature of these and other features on the skull show that they were cut with a rotary wheel
  • SEM image of the moulded details of the internal surface of a crystal goblet from the Museo de las Culturas de Oaxaca: single striations in random orientations are consistent with non-rotary tools
  • SEM image of the moulded details of thetemporal fossai at the sides of the skull: regular parallel striations retained in the polish are consistent with the use of rotary wheel-cutting.
  • A Raman spectrometer being used to study the crystal skull. Photograph courtesy of Laura Jones
  • The upper trace (red) shows the spectrum obtained from the British Museum skull and this can be compared to the lower trace (blue) which is the spectrum obtained from a reference sample of rock crystal
  • Examination of the inclusions within the rock crystal of the British Museum crystal skull. Photograph courtesy of Laura Jones