For forty years I have maintained that it should be possible to date certain old pictographs painted with ochres by archaeomagnetic dating techniques. A 2004 study by Avto Goguitchaichvili and his team used archaeomagnetic dating on ochre paint used to create precolumbian murals in Mexico. “The magnetic measurements of the pigments show that at least four murals retain a remanent magnetization carried by a mixture of magnetite and minor hematite grains.” (Goguitchaichvili et al. 2004) Given that they have proved the feasibility of the process on murals, it stands to reason that it would work on paint deposits on cave walls and other pictographic imagery.
In traditional archaeomagnetic dating clay samples from a feature that has been exposed to high heat, like a fireplace or a adobe brick from a structure that burned down are tested for magnetic orientation. This is then used to calculate the time period that the earth’s magnetic north pole was in the position indicated. “A number of samples are removed from the feature by encasement in non-magnetic plaster within non-magnetic moulds. These samples are marked for true north at the time of collection. The samples are sent to an Archaeomagnetic Laboratory for processing. Each of the samples is measured in a spinner magnetometer to determine the thermal remnant magnetism of each sample. The results are statistically processed and an eigenvector is generated that shows the three-dimensional magnetic declination that will yield a location for the North Pole at the time of the last thermal event of the feature. Data from this feature is compared to the regional secular variation curve in order to determine the best-fit date range for the feature's last firing event.” (Wikipedia)
Now a team of scholars in Mesoamerica have tested the red paint in four Precolombian murals to see if they can be dated archaeomagnetically. The team of scholars involved in the study, aware that archaeomagnetic dates for Mesoamerican sites are relatively few, wanted to study the possibility of retrieving dates on paintings from Precolumbian sites. “For this study, we chose four mural paintings from Central Mexico: Templo de Venus (Cacaxtla culture), Templo Rojo (Templo Mayor of Tenochtitlan), Chapulines and Estrellas (both belonging to the Cholula complex). These sites correspond to the Classic and early post-Classic period in Mesoamerican chronology (approx. 200 to 1200 A.D.).” (Goguitchaichvili et al. 2004)
The results of these tests were very promising, having positive results in all samples. “In summary, 28 samples belonging to four Mesoamerican mural paintings were investigated and the direction of their remnant magnetization was successfully determined. A mixture of magnetite and hematite is responsible for the magnetization, Studied Mesoamerican mural paintings retain the direction of the magnetic field at the time they were painted and are therefore an invaluable source of information concerning secular variation. The archeomagnetic study of pre-Columbian mural paintings opens new alternatives for improving the Mesoamerican absolute chronology.” (Goguitchaichvili et al. 2004) If this is the case in the tested murals, surely it will also apply to many other records painted with ochre paint, such as pictographs and cave painting.
The team of researchers also
triple-checked their results to confirm them. “When researchers compared the magnetic directions of the murals to
directions measured in volcanic rocks dated to the same periods and to other archaeomagnetic
studies of similarly aged lime-plasters, they found rough agreement. And based
on that agreement, they conjecture that the mean direction from three of the
murals corresponds to the interval between A.D. 1000 and 1200.” (Pratt
2004)
In the situation I am proposing the layer of ocher paint will have to be thick enough on the painted surface (cliff, cave wall) to remove a sample. This might be the result of uneven application of paint, or applying paint to a rough stone surface where high and low points on the stone would create a paint layer of varying thickness. While it was still liquid after application the earth’s magnetic field would influence the magnetite and hematite constituents of the paint to orient to the magnetic North Pole as it was then located, and when the paint dried that orientation would be locked in place. This procedure would add a new tool to our collection of dating methods for ancient paintings in addition to radiocarbon dating of charcoal based black pigments. Now some graduate student can take this and run with it - it always feels really good to be vindicated.
NOTE 1: Some images in this
posting were retrieved from the internet with a search for public domain
photographs. If any of these images are not intended to be public domain, I
apologize, and will happily provide the picture credits if the owner will
contact me with them. For further information on these reports you should read
the original reports at the sites listed below.
NOTE 2: For technical details see the paper (Goguitchaichvili et al. 2004) in References below.
REFERENCES:
A. Goguitchaichvili, A. M. Soler, E. Zanella, G. Chiari, R. Lanza, J. Urrutia-Fucugauchi, and T. Gonzalez, 2004, Pre-Columbian mural paintings from Mesoamerica as geomagnetic field recorders, Geophysical Research Letters, 22 June 2004, Vol. 31, No. 12. DOI:10:1029/2004GL020065. Accessed online 3 February 2-25.
Pratt, Sara, 2004, Geoarchaeology - Magnetic Murals, Geotimes Magazine online, September 2004, http://www.geotimes.org/sept04/NN_magneticmurals.html. Accessed online 12 January 2025.
Wikipedia, Archaeomagnetic dating,https://en.wikipedia.org/wiki/Archaeomagnetic_dating. Accessed online 20 November 2024.
Posts
nice Insights
ReplyDelete