Early Copán Acropolis Program 2000 Field Season

Analysis of Activity Residues

During the tunnel excavations a series of samples from various activity areas were taken for later analysis to assist in the reconstruction of ancient behavior. One type of residue that held considerable interest was a very dark stain found in several contexts, including the interior of several masonry drains and both the facades and fills of several structures. One hypothesis held that these dark stains were carbon residues from burning. To test this possibility, permits to export three samples were secured from the Instituto Hondureño de Antropología e Historia. With partial support from FAMSI Grant 99102, these samples were submitted to the Weizmann Institute of Science (Israel) where they were analyzed to identify their content by Ruth Shahack-Gross (one sample from an early Acropolis drain, and samples from the facades of two early Acropolis structures, Yehnal and Sapo). Shahack-Gross and the laboratory where she works at the Weizmann Institute of Science were chosen for their experience in analyzing samples from archaeological sites to distinguish between carbon-based and mineral-based (usually manganese) stains.

The results show that while all three samples contain organic matter, it is not charcoal. On the other hand, two of the three samples also contain manganese oxides which is probably the source of the dark staining. The dark staining in the sample without manganese oxides is unknown, but could be organic.

The complete results by sample were reported as follows:

1. Sample 99M-426 (dark stain from facade of Yehnal Structure): The sample is a light brown sediment composed mainly of calcite, clay and quartz. The sediment was dissolved in hydrochloric acid which dissolves carbonates and phosphates. The resulting insoluble fraction contained mainly clay and quartz, which are silicate minerals. In order to get to the minor components of the sample, we further dissolved it with hydrofluoric acid (which dissolves the silicate minerals). The result showed the sample contains manganese oxides and unidentified organic matter, as its minor components.

2. Sample 99M-427 (dark stain from the facade of Sapo Structure): The sample is a black residue on the surface of a rock. The major components of this residue are calcite, clay and quartz. Similar to the above sample, we dissolved it first in hydrochloric acid and then in hydrofluoric acid. The minor components obtained from the insoluble fraction are manganese oxides and unidentified organic matter.

3. Sample 93M-162 (dark stain from the eastern drain of Yune Platform): The sample is a gray-brown sediment that contains a black layer. This black layer contains, as its major components, calcite, clay and quartz. Following the procedure of acid dissolutions as described above, the minor components found are unidentified organic matter and possible humic substances.

Plans call for additional activity area samples to be analyzed. But for the time being it seems unlikely that any of the analyzed samples represent residues from burning. Rather, the two analyzed dark facade stains seem due to natural deposition of manganese oxides, while the one drain sample seems to be composed of sediments containing minerals and small amounts of humic and other organic materials, all of which would be consistent with the drain’s apparent function as a water conduit.

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