A GEOARCHAEOLOGICAL STUDY OF THE ANCIENT QUARRIES OF SIDI GHEDAMSY ISLAND (MONASTIR,TUNISIA)

Amongst a large number of ancient quarries scattered along the North African coast, those at Sidi Ghedamsy (Monastir, Tunisia) have supplied building stones of Pliocene age. Two lithofacies have been distinguished in the quarry faces: (i) fine sandy limestone, which has been used in the construction of Roman and Arabic monuments; and (ii) porous and coarse limy sandstone, which is of bad quality for construction. Laboratory analysis results confirm that the exploitation of stone in antiquity was well focused on the levels containing the first type. This is confirmed by geotechnical tests, which show that the fine sandy limestone is harder and less porous than the coarse limy sandstone. Extraction of these stones began in the Roman period. The Romans exploited the quarries using steel tools that permitted the extraction of blocks from several levels. In the eighth century, Arabic quarry workers continued the stone extraction using the same technique, but they produced blocks of small and medium size. Statistical measurements have been done on the quarry faces and on the walls of the Ribat in order to understand the degree of conformity between the dimensions of the extracted blocks and those used for building, and ultimately to attempt to date the quarries and the construction of the Ribat.     

THE EFFECT OF SALTS ON THERMAL AND HYDRIC DILATATION OF POROUS BUILDING STONE*

Fifteen desalinated sandstone drill core samples from Umm Ishrin Sandstone Formation in Petra (Cambrian age) were used for this study. The samples were mineralogically analysed using X‐ray diffraction and their physical properties were also determined. Samples with similar physical properties and mineralogical composition were taken for further experimental work. After desalination, thermal and hydric dilatation coefficients were measured, then three types of salts (NaCl, KCl and Na₂SO₄·10H₂O), which have high solubility and consequently are the most dangerous to building stone (and are also detected in the sandstone monuments in Petra), were introduced into the samples and their contents were calculated. The results show that salt crystallization in the pores of building stones can increase their thermal dilatation and decrease their hydric dilatation to varying extents, depending on the nature of the salt. The average increase in the thermal dilatation coefficient per unit mass of salt is the lowest for the Na₂SO₄·10H₂O‐salted samples with a value of 5.3%, while the NaCl‐salted samples have the highest value with 7.8% per salt mass. The average percentage of the decrease of the hydric dilatation coefficient is 1061% for Na₂SO₄·10H₂O‐salted samples per mass of salt content; the NaCl‐salted samples have a value of 1510% per mass of salt content, and the KCl‐salted samples almost the same value. For the salt‐free samples, it was found that in climatic conditions with a high temperature range, the deterioration of sandstone due to temperature fluctuation is more effective than that caused by change in the moisture content, while samples with high salt content suffer more from hydric dilatation.     

MECHANICAL PERFORMANCE OF QUARTZ-TEMPERED CERAMICS: PART I,STRENGTH AND TOUGHNESS*

The effect of quartz temper on the physical and mechanical properties of clay ceramics and the elucidation of the underlying mechanisms that are responsible for these effects are presented here. Characteristics studied included bulk density, open and closed porosity, density of impervious portion and fracture morphology. Mechanical behaviour was studied by measuring energy dissipation during fracture, Young's modulus, initial fracture toughness and strength in flexure. The significant increase in toughness with quartz volume fraction is explained by the development of a model that accounts for the crack distribution around the grains. The archaeological implications of the work are discussed on the basis of all the parameters that might affect the potter's choices of raw materials.     

POROSITY DETERMINATION WITH HELIUM PYCNOMETRY AS A METHOD TO CHARACTERIZE WATERLOGGED WOODS AND THE EFFICACY OF THE CONSERVATION TREATMENTS

The helium pycnometer allows us to measure the cell‐wall density of dry woods and the basic density of wood samples soaked with water and/or a consolidant solution if a non‐volatile solvent is used. These parameters were correlated to the porosity, which for degraded waterlogged wood is related to the maximum water content. Moreover, this has revealed the possibility of investigating, by means of accurate cell‐wall density determination, the efficacy of several consolidants in the treatment of waterlogged woods.     

A WATER ABSORPTION ANALYSIS OF NABATEAN,NORTH AFRICAN AND OTHER CLAY LAMP FABRICS UNEARTHED AT THE RED SEA PORT OF ROMAN AILA (AQABA,JORDAN)*

A water absorption analysis was conducted on 103 clay lamp samples to determine whether the fabrics of this pottery type are porous. If so, this would lend further support to the long‐standing assumption that lamp makers coated their lighting vessels with slip—not just for decorative purposes, but as a means of preventing oil seepage of the fuel chamber. The samples were excavated at the Red Sea port of Roman Aila (modern Aqaba, Jordan) and belong to 10 different types originating from Arabia, Palestine, Egypt, Tunisia and Gaul. The results of the experiment reveal that clay lamp fabrics are porous, and comparatively more so than a reference group of non‐lamp pottery from Pella (Jordan). Petrographic thin‐section analysis of select fabrics confirms the presence of pores, cracks and propagating veins indicative of thermal stress resulting from repeated lamp use. Meandering veins identified in a nozzle fragment were created by the diffusion of vapours, probably originating from the burning lamp oil itself. Ancient lamp makers understood that, given its direct exposure to the extreme temperature of the flame, the nozzle was particularly vulnerable to breakage as a result of thermal shock. A porous lamp fabric, however, helped limit crack propagation, allowing the nozzle and the lamp body to expand and contract to avoid breakage.     

The Origin of Soluble Salts in Rocks of the Thebes Mountains, Egypt: The Damage Potential to Ancient Egyptian Wall Art

Soluble salts are indigenous to the marine sediments of the Esna Formation and Thebes Formation in central Egypt. Natural weathering processes and human impact cause salt efflorescence in tombs and on walls of ancient Egyptian monuments in the Theban Necropolis, resulting in the disintegration of wall paintings and carved hieroglyphs. Determination and quantification of soluble salts and measurements of the porosity were done on tomb marls in order to understand the origin and damage potential of the salts in the royal tombs of the Valley of the Kings. The study shows that sodium chloride (NaCl) is the predominant salt species. Sulphates, anhydrite (CaSO₄) and gypsum (CaSO₄ . 2 H₂O) also occur in the limestone deposits of the Thebes Formation and the underlying shale deposits of the Esna Formation. Member I of the Thebes Formation, into which most of the ancient tombs were hewn, shows the highest amount of soluble salts (up to 6·2 wt-% dry). In addition, the porosity and permeability of the marls in Member I are high, enhancing water molecules and brine migration. Wetting and drying of the tomb surfaces in the past has affected solution, transportation and recrystallization of water soluble minerals, and has led to major destruction of wall paintings and ornamentations. This study shows that large amounts of salt minerals still remain in the wall rocks. Future humidity changes due to flash floods and tourists may favour salt crystallization in the ancient Egyptian monuments. The authors urge the authorities to undertake steps to prevent further destruction to save the magnificent cultural heritage found in the Thebes area.     

DETECTING AND QUANTIFYING HEAT TREATMENT OF FLINT AND OTHER SILICA ROCKS: A NEW NON‐DESTRUCTIVE METHOD APPLIED TO HEAT‐TREATED FLINT FROM THE NEOLITHIC CHASSEY CULTURE,SOUTHERN FRANCE

Heat treatment of lithic raw material is known from the Middle Stone Age to the Neolithic. These findings require archaeometric techniques and methods for detecting the heat‐induced effects within lithic artefacts. However, the existing methods are often cost‐intensive and time‐consuming, and most of them are destructive. Here, we present a new method using the infrared spectroscopic measurement of the strength of H‐bonds formed between surface silanole groups (SiOH) and H₂O molecules held in open pores of the samples. The reduction of H‐bond strength in chalcedony is shown to be strongly correlated with the loss of open pores induced by heat treatment. Hence, the method is based on measuring one of the transformations aimed for by the instigators of the heat treatment: the reduction of porosity that modifies the rock's mechanical properties. A first application to heat‐treated material from the Neolithic Chassey culture (southern France) shows that flint was heated to temperatures between 200°C and 250°C in this period. This has important implications for the study of the procedures used and the heating environments. Our new method is non‐destructive, rapid, cost‐effective and allows for detection of the used annealing temperatures.     

MECHANICAL PERFORMANCE OF QUARTZ-TEMPERED CERAMICS: PART II,HERTZIAN STRENGTH,WEAR RESISTANCE AND APPLICATIONS TO ANCIENT CERAMICS*

Mechanical performance of ceramics can be measured by various techniques. Conventional testing usually requires multiple samples of large size and specific geometries and for this reason cannot be usually applied directly to ancient pottery. However, Hertzian strength and wear resistance can be measured on the same specimen, of small size, and it is shown that these tests can describe, to a good approximation, the basic ceramic mechanical propertics (strength and toughness). Therefore, these tests are proposed for use on archaeological specimens. An application on Punic amphorae found in Corinth is presented.