February 2016 Issue Table of Contents
1811-5209/16/0012-$0.00 DOI: 10.2113/gselements.12.1.3
My first exposure to cultural heritage occurred in 1974 when I was asked by a group of physicists from the Stanford Research Institute (now SRI International based in California, USA) to serve as a mineralogical consultant for their project on the pyramids of Giza (Egypt). Their objective was to perform radio frequency (rf) sounder experiments in search of archaeologically significant hidden chambers. I carried out powder X-ray diffraction and optical emission spectrographic analyses of limestone chips from the Giza pyramids. The high water content of the analyzed limestones, the high relative humidity (80%) inside the pyramids, and the hydrous clay minerals found in the limestone helped explain the high attenuation of the rf signal, which prevented any new chambers from being located (Dolphin et al. 1975). About 10 years later a major controversy erupted when Frenchman Joseph Davidovits suggested that the blocks comprising the Giza pyramids were cast in place using limestone aggregate and a wet alkali aluminosilicate binder (i.e. geopolymeric limestone concrete blocks) rather than having been quarried (Davidovits 1987; Davidovits and Morris 1988). This opinion was challenged a few years later by Robert Folk, the well-known sedimentary petrologist at the University of Texas Austin (USA), who conducted field and laboratory studies of the Giza pyramids and of the limestone from the local Tura quarries, which are thought to be the source of the limestone blocks for the Khufu pyramid (the Great Pyramid) at Giza (Campbell and Folk 1991). More recently, material scientists from Drexel University (Philadelphia, USA) carried out microstructural analyses of nine samples of the stones comprising the Giza pyramids using scanning and transmission electron microscopies (SEM and TEM), coupled with energy dispersive X-ray analyses (EDXA) (Barsoum et al. 2006). Barsoum and colleagues concluded that while most of the blocks, especially those in the core, were indeed quarried and carved, some blocks at or near the surface (casing stones) appear to have been cast in place using a primitive limestone-based cement. However, in reviewing this more recent study, I am not convinced that the mineralogical work is definitive, due to the authors’ reliance on SEM–EDXA for identifying phases and their lack of any X-ray or electron diffraction data on the samples, which would have provided more definitive results on the identity of the crystalline phases. This ongoing controversy about how the pyramids of Giza were built illustrates the important role of modern analytical methods in cultural heritage, which is the subject of this special issue of Elements.
Another example of the use of modern analytical methods in archaeology involves Archimedes of Syracuse (Sicily, now Italy but formerly a part of Greece), the famous Greek mathematician and scientist who lived from ~287 BC to ~212 BC. His well-known contributions to mathematics and science are wide-ranging, particularly his discovery—according to legend while taking a bath—of how to measure the volume (and density) of an irregularly shaped object by the amount of water it displaces. In 1906, Danish scholar Johan Heiberg discovered a battered manuscript at the Church of the Holy Sepulchre in Constantinople (Turkey) written on recycled parchment and containing strange Greek writings, mysterious drawings, and mathematical symbols, most of which were covered by more modern paintings. He recognized that the faint material was from Archimedes, including the only surviving copy of On Floating Bodies in the original Greek. However, Archimedes ideas had been recorded by the monk Johannes Myronas in 1229 rather than by Archimedes himself. Let’s fast forward to 2003 when my SLAC National Accelerator Laboratory colleague Dr. Uwe Bergmann decided to try to decode Archimedes writings in the famous palimpsest using the X-ray fluorescence signal from the iron-based pigment employed by Myronas to record seven of Archimedes’ treatises. As shown in FIGURE 1, using extremely intense synchrotron light, Uwe was successful in “seeing” through the overlying paint on ancient parchment and uncovering the hidden writings in what is now termed the Archimedes’ Palimpsest. Uwe’s conclusion in his 2007 Physics World article is particularly appropriate for this issue of Elements: “In a fascinating cycle spanning more than two millennia, it is fitting that one of the most advanced tools of modern physics – the particle accelerator – should make such a big contribution to our understanding of this genius from ancient Greece who had so significant an impact on modern science.”
These two examples of the application of modern analytical methods to archaeology and cultural heritage stand in stark contrast to the approaches employed by archaeologists prior to World War II, as popularized by the fictional character Indiana Jones in movies such as Indiana Jones and the Last Crusade, set from 1912 to 1938, and Raiders of the Lost Ark, set in 1936. “Indy’s” adventuresome spirit and keen eye could not have resolved the controversy about how the pyramids of Giza were built and could not have detected the hidden writings of Archimedes beneath layers of more modern pigment on recycled parchment. Real archaeologists of that era would have been astounded by what today’s analytical methods, especially those using synchrotron light, can detect and see.
The six articles in this issue of Elements show the power of modern analytical and geophysical methods that are commonly used in the geosciences but now applied to characterizing, interpreting, and conserving cultural heritage. Hopefully, this issue will stimulate a greater involvement of geoscientists in future studies of our cultural heritage.
Barsoum MW, Ganguly A, Hug G (2006) Microstructural evidence of reconstituted limestone blocks in the Great Pyramids of Egypt. Journal of the American Ceramic Society 89: 3788-3796
Bergmann U (2007) Archimedes brought to light. Physics World 20: 39-42
Campbell DH, Folk RL (1991) The ancient Egyptian pyramids – concrete or rock? Concrete International 13: 28, 30-39
Davidovits J (1987) Ancient and modern concrete: what is the real difference? Concrete International: Design and Construction 9: 23-35
Davidovits J, Morris M (1988) The Pyramids: An Enigma Solved. Hippocrene Books, New York, 280 pp
Dolphin LT and 11 coauthors (1975) Electromagnetic Sounder Experiments at the Pyramids of Giza. Stanford Research Institute Report to the Office of International Programs, National Science Foundation, Washington, D.C. Accessed at http://www.ldolphin.org/egypt/egypt1/.