| Summary: | Lime and gypsum plasters and mortars are an important class of architectural materials that were first developed in the Near East some 11,000 years ago. This study examines changes in the technology of production and use of these materials at Petra and Udruh, south Jordan. It aims to understand the technological developments during a sequence of time periods and to explain the use of certain mixes for specific applications. It concentrates upon the Nabataean/ Roman/ Byzantine transitions in order to define the technological styles of their production in each period and to examine the technological exchanges of knowledge in both directions that occurred through imperial conquest. This study has developed an independent chronology by radiocarbon dating of the samples' lime-binder and organic inclusions. Stepped-dissolution techniques were developed to overcome the problem posed by the addition of unburnt limestone aggregate to burnt lime plasters, and the method was tested successfully on samples of known age at Petra. The technology of plaster and mortar production was studied by X-Ray diffraction, scanning electron microscopy, cathodoluminescence, and optical petrography, supplemented by measurements of porosity, aggregate/binder ratios and grain size distributions. I found that the Romans made changes to the Nabatean recipes used for binding and for coating with multiple layers, but they made no changes to the plaster recipes used to line cisterns and canals. The Byzantines produced plasters by combining Nabatean and Roman recipes to produce coating plaster of lower quality. Ayyubid and Ottoman samples at Udruh are of low quality (soft, very porous, and rich in organic inclusions). In summary, Results support the claim that Petra was not abandoned during the Byzantine period. It found that the Nabateans used a diversity of recipes and the Romans used lime-plaster only, crushed ceramics were used from early Hellenistic to late Byzantine times, and it is unwise to use only color to differentiate between Nabatean and Roman mortar.
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