Santander, February 19th-22nd 2008 - Aranzadi

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HORTENSIA DE VEGA, EMILIANO R. MELGAR, M. DE LOURDES GALLARDO
de arqueología experimental en materiales conquiológicos”
and “Proyecto de técnicas de manufactura
del México prehispánico”, both under the
direction of Adrián Velázquez (2007).
The first project has an experimental archaeology
workshop where different types of modifications
of Ancient Mexico shell objects are reproduced
(abrading, cuts, holes, incisions, and finishing),
using tools and techniques referred in
codexes and historical documents, or data recovered
from archaeological contexts. In the second
project, the manufacture traces are analyzed
comparing them with archaeological specimens
in three levels: macroscopic, using an optical
microscope at 10x, 30x and 63x and with scanning
electron microscopy (SEM) at 100x, 300x,
600x and 1000x in high vacuum mode (HV) with
signal of secondary electrons (SEI), and voltage
of 20 kV.
To avoid the need to apply a conductive coating
over the pieces, detailed impressions were
made with a thin tape of polymer with one drop of
acetone, pressed it over the area that we want to
analyze for one minute until it is dry. After that, we
mounted each replica sample on 30 mm diameter
aluminium stubs and coated all of them with
an ultrathin coating of electrically-conducting
material, commonly gold, by low vacuum sputter
coating. By this way, we could analyze oversized
pieces bigger than the 10 cm of the SEM chamber,
avoid the movement of the objects from the
museums to the lab, and optimize the time invested
in the SEM by analyzing 20 samples per two
hours. Following this technique, we had a 165
pieces sample of the 1664 total pieces for the
stereoscopical microscopy, and 28 for the SEM,
in order to observe the abrading, edges, holes
and polishing.
The surfaces were abraded with lithic tools,
without abrasives, because of the presence of
intercrossed lines (Fig. 4). With the microscopical
analyses we observed rounded bands of 100
microns width, that correspond to the ones produced
experimentally with basalt (Fig. 5).
Figure 4. Archaeological surface (a) and experimental abrading with basalt (b) at 10x.
Figure 5. Archaeological surface (a) and experimental abrading with basalt (b) at 100x.
MUNIBE Suplemento - Gehigarria 31, 2010
S.C. Aranzadi. Z.E. Donostia/San Sebastián