Research news
Study of two large crystal skulls in the collections of the
British Museum and the Smithsonian Institution
British Museum 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 (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 
decades. 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
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 o
f 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 b
e 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 
were 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.
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.
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.
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 a
lso 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