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and mixed with the body of the stone, or the body limestone somehow merged or melted with the surface layer. Lastly and most unlikely, the limestone constituents could have been a part of the added surface layer. If this were true, the second and third spectra would have been more similar. and mixed with the body of the stone, or the body polishing. The layer has the composition, sheen, limestone somehow merged or melted with the surface _ hardness and glassy texture of a glaze. layer. Lastly and most unlikely, the limestone The results strongly indicate that heat was used to constituents could have been a part of the added produce the surface layer, which raises several surface layer. If this were true, the second and third questions. Even if a layer of a ceramic paste had been spectra would have been more similar. applied, how was the whole heated to the requisite temperatures without cracking the limestone? It tends Conclusions to shatter at such high heat levels. The body stone is limestone, but the surface is more How was the heat produced to treat these structures? complicated. Its spectrum shows some similarity to While this sample is from a cave, there are similar wollastonite, which forms when impure limestone is structures outside with the same kind of glaze. The subjected to high temperatures and pressures. same conclusion cannot necessarily be applied to these However, the impurities that are seen in the surface are _ other cases. not present in similar amounts in the stone body. This Chemical analysis is needed, but the similarities with indicates that the compounds in the surface layer were the investigated sample and other photographed cases most likely added. Other stone types may be are clear. It is likely that these other cases are also comparable, but they cannot have formed naturally in __ vitrified. The amount of heat needed to fire the huge he layer on the man-made surface. It appears that the — stones on which these glazes are found would have surface layers were applied and treated with heat. This | been enormous. In furnaces, the whole body has to be option does have some merits, but it is moving towards __ raised to the temperature of the surface glaze. This is he arcane world of the done slowly over the course of ceramist. many hours. How the heat If an antique ceramic sample g g would have been produced is is compared to the spectra of Even if a layer of a ceramic unknown. he glaze above, there is little to paste had been applied, h . Inth i i "eoray techniques ‘applied to how was the whole PSION ed stones provoke surface paintings of ceramic heated to the requisite much debate. Faplenations on pottery pieces from Aguada . ow the forms were produce Culture (Catamarca, Argentina)", temperatures without vary from the use of advanced here are several comparable cracking the limestone? machines, simple metal or results. The samples are from stone tools, moulds, pottery pieces from Argentina, concentrated sunlight and fire so an exact match is unlikely. methods. While the analysis These researchers tested a variety of different-coloured above says little about the way the shapes were made, it samples from Argentine pottery shards with residual does eliminate some ideas on the means of producing gold leaf on the surface. The spectra are surprisingly these exquisite finishes. similar if the gold leaf is ignored, along with the The finish on the stone sample is not the thickest, manganese and iron. The latter two elements have _ shiniest or glassiest of the examples. However, its oxides that are common colorants in ceramic pastes. composition and morphology are the same as a ceramic This is the source of the various colours discussed in glaze. This means that heat was somehow applied to their research paper. The key constituents silicon, the stone. How the heat was applied is not clear. What aluminium, magnesium, carbon and oxygen are present _ is clear is that an unknown technology was used. To in the same ratios. create ceramics on this scale, the heat must have been While the abovementioned spectra do not show _ greater than that used in normal ceramic production explicitly that the surface is vitrified, the composition is | methods. that of a glaze. It has a different make-up to the The most referenced work on the stonework of Peru limestone body. This means it is very likely that the | was produced by Professor Jean-Pierre Protzen. His glaze was made from a ceramic paste applied to the work deals primarily with the carving of the stones with limestone surface. This is clear from the comparison primitive tools. However, Prof. Protzen has looked at with the ancient glazed ceramic pottery shards. these effects and has suggested that they could have The microscope photographs of the surface do not been achieved with polishing. To date, only andesite show the amorphous state of the layer. This can be polishing has been attempted, with very limited shown explicitly by electron microscope analysis. success. Further studies need to be carried out to confirm the After considering the above analysis of the surface state of the layer. The different chemical composition layer, it is clear that polishing alone will not produce the makes it very unlikely that this surface was created by requisite heat needed to produce a ceramic glaze. This Even if a layer of a ceramic paste had been applied, _ how was the whole heated to the requisite temperatures without cracking the limestone? NEXUS ¢ 63 AUGUST - SEPTEMBER 2012 www.nexusmagazine.com