Development and validation of non-invasive chemical methods for cleaning of palaeontological specimens
Date
2009-05-22T11:37:39Z
Authors
Pole, Stephen
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The dolomitic cave deposits of southern Africa hold arguably the most abundant
hominid and fauna fossil record in the world. However, as a result of various mineral
processes occurring, these fossils are often covered in a brown/black deposit. This
layer is a mixture of manganese and iron oxides from mineral dissolution of the
dolomite in cave environment in which all the specimens are found. This covering
presents a particularly complex problem as it obscures fine surface details (e.g. cut
marks and carnivore tooth marks) on the bone that are of particular interest in the
fields of palaeontology and palaeo-anthropology. Being able to identify and
distinguish between different modifying agents is important for interpreting how the
bones were transported into the cave.
The deposit of manganese oxides was successfully removed from the bone using
hydrogen peroxide, nitrites, chromium(III) and hydroxylamine without visibly
altering the bone composition and structure, leaving all surface markings unaltered
from their original state. It has been established that the above reagents can be used to
reduce the manganese oxides resulting in Mn2+ as the main product of the reactions.
The concentration of reagents, reaction time and other conditions were optimised. The
hydrogen peroxide method has been applied in the cleaning of over seven thousand
manganese oxide coated fossil bones and teeth from the early hominid site of Coopers
D situated in the Cradle of Humankind. A flow through system was also constructed
and used for the mass cleaning of fossils using the hydrogen peroxide method and the
hydrogen peroxide was continually replaced to maintain the [H+] and remove the Mn2+ formed, and thus drive the Mn4+ reduction reaction. Validation and analysis of
cleaning methods included pH, time, Mn2+ concentration as well as the Mn: Fe ratio
determination. Although the chromium method was proved successful in removing
the fossil bone coatings, the kinetics for this surface reaction were extremely slow.
Qualitative validation of all these methods was performed by gravimetric analysis and
through the use of scanning electron microscopy and proved that the manganese oxide
removal does not damage bone matrix. Characterisation of the mixed oxide coatings
was performed using powder X-ray diffraction, X-ray fluorescence mapping, Raman
spectroscopy and Infrared spectroscopy. These chemical procedures of selectively
removing the dark manganese oxide coating from fossils to expose surface
modifications, is a breakthrough for the fields of palaeontology and archaeology and
sub-disciplines concerned with fossil bones.