Radiocarbon (carbon-14) Dating of Book of the Dead of Sobekmose
Radiocarbon (carbon-14) Dating of Book of the Dead of Sobekmose
Rachel Danzing – Brooklyn Museum
Our research to further understand the Book of the Dead of the Goldworker Amun, Sobekmose continues. Carbon-14 (C-14) dating was one of the first scientific analytical techniques that we employed to confirm the date for this piece, thought to be approximately 1420 B.C.E. based on previous research.
Detail from the Book of the Dead of the Goldworker Amun, Sobekmose. New Kingdom, Dynasty 18, ca. 1479-1400 B.C.E. Ink and pigment on papyrus. Brooklyn Museum, Charles Edwin Wilbour Fund, 37.1777E.
For several reasons, it is a rare opportunity for us to test Museum objects using this technique. One necessary condition is that the object must fit into a certain time range. C-14 dating requires that the material in question be at least 2,000 years old (and up to 50,000 years old) to get a result with a significant certainty. Fortunately, we believed our papyrus fit into this time range.
Additionally, with works of art on paper, we do not often have an expendable sample for this type of analysis. Unlike the Fourier-Transform Infrared Spectroscopy and X-ray Fluorescence Spectroscopy described in the two previous posts which require no sample and were used to investigate pigments and adhesives used on the papyrus, C-14 dating requires a sample from the object, usually about 5 mg, which is destroyed during testing. After placing as many loose fragments as best as possible (we will talk more about our repairs in a future post), we had some very small ones remaining with no ink or coloring which were unplaceable. We consulted with our curators and decided that we could use a few of these small fragments for C-14 analysis.
Fragments circled are approximately 5 mg of sample.
There are only a handful of labs in this country that do this kind of analysis. We sent our sample to the Accelerator Mass Spectrometry (AMS) laboratory in the Physics Department at the University of Arizona in Tucson for analysis. C-14 dating was developed after World War II in the 1940s and 1950s and the principal is based on the measurement of the unstable carbon isotope 14C levels in a sample as compared to modern, known standards of the stable carbon isotopes 12C and 13C, which comprise the great majority of atmospheric carbon. (Isotopes are different forms of the same element.) The 14C atoms are produced when cosmic rays bombard the Earth’s upper atmosphere and produce nuclear reactions which produce neutrons. (About 2 atoms per second per centimeter squared are produced.) These neutrons react with nitrogen atoms to form 14C atoms, an unstable form of carbon. 14C mixes up into the atmosphere and is taken in by plants during photosynthesis, and other organisms as part of the food chain.
The 14C in an organism is always being replenished from the atmosphere at a constant rate while it is alive, and the ratio between it and the stable carbon isotopes is approximately constant with time. But when a plant or organism dies, its 14C intake stops and what remains will decay at a known rate (half life of 5,730 years). Therefore by measuring the amounts of the 14C and comparing it to known 12C data, an approximate age can be determined.
Spectra of C-14 results from University of Arizona AMS laboratory.
Our results are given in the spectra above. With some interpretation this shows that the results we received from the C- 14 method of scientific analysis are indeed consistent with our current understanding of our Book of the Dead, i.e. that it was produced in the New Kingdom, Dynasty 18, c. 1420 B.C.E.
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This post is part of a series by Conservators and Curators on papyrus and in particular the Book of the Dead of the Goldworker of Amun, Sebekmose, a 24 foot long papyrus in the Brooklyn Museum’s collection. This unique papyrus currently in 8 large sections has never been exhibited due to condition. Thanks to a generous grant from the Leon Levy Foundation, the entire papyrus is now undergoing conservation treatment. The conservation work is expected to last until fall 2011 when all 8 sections will be exhibited together for the first time in the Mummy Chamber. As each section is conserved, it will join those already on exhibition until eventually the public will see the Book of the Dead in its entirety.