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Evidence of Vitrified Stonework in the Inca Vestiges of Peru (cont.)
By Jan Peter de Jong & Christopher Jordan


The body stone is limestone, but the surface is more complicated. Its spectrum shows some similarity to Wollastonite, which forms when impure limestone is subjected to high temperatures and pressures. However, the impurities that are seen in the surface are not present in similar amounts in the stone body. This indicates that the compounds in the surface layer were most likely added. Other stone types may be comparable, but they cannot have formed naturally in the layer on the man made surface. It appears they were applied and treated with heat. This option does have some merits, but it is moving towards the arcane world of the ceramist.

If an antique ceramic sample is compared to the spectra of the glaze above there is little to separate the two. In the Paper X-Ray Techniques Applied to Surface Paintings of Ceramic Pottery Pieces From Aguada Culture (Catamarca, Argentina) there are several comparable results. The samples are from pottery pieces from Argentina so an exact match is unlikely. These researchers tested a variety of different colored samples from Argentine pottery shards, which had residual gold leaf on the surface. The spectra are surprisingly similar if the gold leaf is ignored along with the Manganese (Mn) and Iron (Fe). The latter two elements have oxides that are common colorants in ceramic pastes. This is the source of the various colors in their research paper. The key constituents Silicon, Aluminum, Magnesium, Carbon and Oxygen are present in the same ratios.

Whilst the spectra do not show explicitly that the surface is vitrified, the composition is that of a glaze. It has a different makeup to the limestone body. This means it is very likely that the glaze was made from a ceramic paste applied to the limestone surface. This is clear from the comparison with the ancient glazed ceramic pottery shards.

The microscope photos above of the surface do not show the amorphous state of the layer. This can be shown explicitly by electron microscopic analysis. Further analysis needs to be carried out to confirm the state of the layer. The different chemical composition makes it very unlikely that these surfaces were created by polishing. The layer has the composition, sheen, hardness and glassy texture of a glaze.

The results strongly indicate that heat was used to produce the surface, which raises several questions. Even if a layer of a ceramic paste was applied, how was the whole heated to the requisite temperatures without cracking the limestone? It tends to shatter at these sorts of heats.

How was the heat produced to treat these structures? Whilst this sample is from a cave, there are similar structures that are outside with the same kind of glaze. The same conclusion cannot necessarily be applied to these other cases.

Chemical analysis is needed, but the similarities with the investigated sample and other photographed cases, are clear. It is likely that these other cases are also vitrified. The amount of heat needed to fire the huge stones on which these glazes are found is enormous. In furnaces, the whole body has to be raised to the temperature of the surface glaze. This is done slowly over the course of many hours. How the heat would have been produced is unknown.

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