MECHANICAL PROPERTIES OF STONE ARTEFACT MATERIALS AND THE EFFECT OF HEAT TREATMENT*

Mechanical testing of lithologies used for stone tool manufacture has shown that fracture toughness is the most objective measure of the quality of raw materials shaped by either flaking or pecking/grinding. Materials amenable to pressure flaking and blade manufacture have low values of fracture toughness, whereas those shaped by pecking/grinding have high values. The fracture toughness test is also the most definitive for quantifying the improvement in flaking properties of materials subjected to intentional heat treatment. Cryptocrystalline and macrocrystalline siliceous lithologies demonstrate a well-defined, gradual reduction in fracture toughness with increased temperature. When heated to optimum temperatures, their fracture toughness approaches that of obsidian, the lithology generally regarded as having the best flaking properties.     

Color Me Heated? A Comparison of Potential Methods to Quantify Color Change in Thermally-Altered Rocks

This study investigates and compares methods to quantify color changes in quartzite rocks after repeated heating episodes. We collected quartzite samples from the southern Cape coast, South Africa, and heated them three times in experimental fires. We recorded the colors of the samples before and after heating using visual observation, Munsell color notations, Munsell color notations converted to RGB values, and digital image analysis. The methods are also tested on potentially heated and potentially unheated archaeological samples from Klasies River main site, South Africa. It was possible to distinguish between unheated and repeatedly experimentally heated quartzite using visual observation and Munsell color notation, but a large proportion of repeatedly heated samples appeared unaffected by the heat. The digitally-captured color values best discriminated color changes after heating. Color values of repeatedly heated experimental samples overlap with color values of potentially heated archaeological samples.     

Heat treatment of Polish flints

In Poland three types of flint (chocolate, spotted and banded) were intensively mined from the Terminal Palaeolithic to the Early Bronze Age. Although heating of flint to improve its flaking properties was practised across the world from ∼110,000 years ago to the recent, particularly in southwestern Europe, heat treatment of flint in Poland is known from only two sites.     

Heat treatment in the South African Middle Stone Age: temperature induced transformations of silcrete and their technological implications

It was recently found that silcrete raw material was heat-treated during the South African Middle Stone Age (MSA) for altering its flaking properties. This finding led to hypotheses about the implications for the MSA hunter-gatherers such as the cost of thermal treatment in terms of investment and firewood. To date, these hypotheses lack a solid basis, for data on the thermal transformations of South African silcrete and, hence, the necessary heating procedure and heating environment, is missing. In order to produce such data, we conducted an experimental study within the framework of the Diepkloof project. This work is based on the petrographic, mineralogical and structural analysis of South African silcrete from the West Coast and its thermal transformations. Our results shed light on the nature of these transformations, the ideal heating temperatures and the tolerated heating speed. The processes occurring in silcrete are comparable to flint, i.e. the loss of chemically bound ‘water’ and the formation of new Si–O–Si bonds, but their intensity is less pronounced. Effective heating temperatures are significantly higher than for flint and the heating speed tolerated by South African silcrete is relatively fast. These findings imply that silcrete heat treatment cannot be directly compared with flint heat treatment. Unlike flint, heating silcrete does not require the setup of a dedicated heating environment and may have been performed in the same time as other fire related activities. This would represent only a minor supplementary investment in time and firewood. These results have broad implications for the discussion about technological evolution and the acquisition of specialised knowledge in the MSA.     

Responses of South African Agate and Chalcedony When Heated Experimentally,and the Broader Implications for Heated Archaeological Minerals

Here we present a database of responses by South African agate and chalcedony to heat treatment. This will assist analyses of heated stone tools not only in South African archaeological sites, but wherever heated agate and chalcedony pieces were knapped. The minerals are abundant worldwide. To replicate potential heating methods during the Stone Age we placed some minerals in a wood fire, some under coals, and others were buried in sediments beneath fires. Thermal responses include lustrous flaked surfaces, pot lid fractures, semi-circular internal fractures, rough internal surfaces, and crazing. Aerobic heating is implied by pot lid fractures. To explain the thermal responses we analyzed the minerals using X-ray fluorescence, Raman spectroscopy, and carbon and sulfur analyses. Our chalcedony contains more water and impurities than agate, making it more vulnerable to thermal damage. Our method of combining field experiments with chemical analyses has global applications even though we expect that mineral components of agate and chalcedony will vary slightly in different parts of the world.     

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.     

Evolution of the transport properties of fractures subject to thermally and mechanically activated mineral alteration and redistribution

Strong feedbacks link temperature (T), hydrologic flow (H), mechanical deformation (M), and chemical alteration (C) in fractured rock. These processes are interconnected as one process affects the initiation and progress of another. Dissolution and precipitation of minerals are affected by temperature and stress, and can result in significant changes in permeability and solute transport characteristics. Understanding these couplings is important for oil, gas, and geothermal reservoir engineering, for CO2 sequestration, and for waste disposal in underground repositories and reservoirs. To experimentally investigate the interactions between THMC processes in a naturally stressed fracture, we report on heated (25°C up to 150°C) flow‐through experiments on fractured core samples of Westerly granite. These experiments examine the influence of thermally and mechanically activated dissolution of minerals on the mechanical (stress/strain) and transport (permeability) responses of fractures. The evolutions of the permeability and relative hydraulic aperture of the fracture are recorded as thermal and stress conditions' change during the experiments. Furthermore, the efflux of dissolved mineral mass is measured periodically and provides a record of the net mass removal, which is correlated with observed changes in relative hydraulic fracture aperture. During the experiments, a significant variation of the effluent fluid chemistry is observed and the fracture shows large changes in permeability to the changing conditions both in stress and in temperature. We argue that at low temperature and high stresses, mechanical crushing of the asperities and the production of gouge explain the permeability decrease although most of the permeability is recoverable as the stress is released. While at high temperature, the permeability changes are governed by mechanical deformation as well as chemical processes, in particular, we infer dissolution of minerals adjacent to the fracture and precipitation of kaolinite.     

The Influence of Indoor Climate Control on Risk for Damages in Naturally Ventilated Historic Churches in Cold Climate

This article analyzes the indoor climate that creates risk of damages in naturally ventilated churches in the cold climate of Estonia. Indoor temperature and humidity were measured over a one-year period and the results were analyzed on the basis of damage functions: mold growth, risk of cracking and fracturing of wooden objects, and delamination of the gesso layer of panel paintings.

In unheated churches, one of the most dominant problems was very high relative humidity throughout the year, creating a high risk for mold and algae growth. Churches may need background heating to avoid freezing during a long cold winter that causes low surface temperatures of massive walls during the spring–summer period. It was found that mold risk was significantly lower in heated churches than in unheated or intermittently heated churches. The risk of mold growth was not decreased by the use of intermittent heating.

In heated churches, overheating (room temperature >+10ºC) causes a RH below 50% during cold periods, and the favorable period for irreversible response of panel paintings was significantly longer, so there is a higher risk that the gesso may crack or delaminate. From the point of view of the cracking and fracturing of wood, indoor climate conditions are in the safe range for most of the year.     

The use of electron spin resonance spectroscopy to determine the thermal histories of cereal grains

The thermal histories of archaeological cereal grains have been explored with electron spin resonance spectroscopy by a quantitative study of pyrolysis-induced radical carbon. Comparison with modern samples of heated cereal grain has shown that the g value of the radical carbon signal is characteristic of exposure to a previous maximum temperature, and studies of other signal parameters suggest that further information, such as the duration of previous heating, may be deduced from such studies. The proposed method offers the possibility of quantitatively rigorous measurement in archaeological studies of cultural and technological processes that previously relied upon subjective assessment.     

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.     

Testing for the presence of thermal pretreatment of flint in the mesolithic and neolithic of Sweden

Through ethnographic accounts, the method of heat treatment of silica materials to improve the flaking qualities is shown to have been known almost worldwide. Some mesolithic and neolithic flint artifacts from southern Sweden were examined in order to determine if they too were heat treated. From several methods proving or indicating thermal alteration of flint, analysis using scanning electron microscopy was chosen. Two samples were taken from each artifact, one being examined unaltered, the other being heat treated. No two samples from the same artifact had the same kind of surface appearance. Thus these analyses prove that the artifacts examined had not been heat treated.     

Numerical Assessment of Frictional Heating in Sliding Bearings for Seismic Isolation

This article proposes a numerical investigation of the frictional heating developed in sliding bearings under high velocities and the influence of the relevant temperature rise on the mechanical characteristics of the device. A three-dimensional finite element model of the bearing is created and frictional heat generation is modelled through a thermal source inserted at the sliding surface of the bearing, with intensity dependent on the coefficient of friction, the contact pressure and the velocity. The friction value is adjusted step-by-step on surface temperature and velocity and used to update the thermal flux and the resisting force developed by the bearing. The numerical predictions of temperature histories and force–displacement loops are compared with the results of laboratory tests to validate the numerical approach. The procedure can help in preliminary studies for the selection of bearing materials accounting for their thermal stability and for the estimation of change of design properties of sliding isolation bearings due to frictional heating.     

Thermally Altered Novaculite and Stone Tool Manufacturing Techniques

Abstract

This paper describes a study of the physical origins of improved flaking properties, called flakeability, for novaculite, a material exploited for stone tool manufacture by the peoples of prehistoric Arkansas, Missouri, Texas, and Louisiana. Experimentation in thermal pretreatment and ways to detect and discriminate the results of this pretreatment were carried out. The criteria derived for distinguishing this alteration in the novaculite are easily determined by a straightforward analysis that can be done in almost any laboratory.

The results of this experimentation have direct implications for the study and identification of thermal pretreatment in this and other stone materials. From the correlations between the physical alteration of such source materials and the implication for manufacturing techniques, the archeologist can more validly infer relationships between prehistoric lithic technology and the knappers who developed highly diversified and specialized techniques. Such experiments combined with wear analysis, material source determination, and other lithic studies will allow the archeologist to delineate manufacturing and exploitative patterns and examine their relationship to all forms of cultural and environmental variables.     

AN X-RAY DIFFRACTION STUDY OF HEAT-TREATED CHERT AND ITS ARCHAEOLOGICAL IMPLICATIONS

It has been established that on occasion prehistoric man heat-treated siliceous stones in order to improve their flaking qualities. In this work we have examined samples of heat-treated chert by means of X-ray diffraction and have established that, in most cases, heat treatment causes an X-ray diffraction line broadening which can be interpreted as a decrease in range of crystalline order of up to 40%, in the most extreme case. The implications of this to an understanding of the fundamental mechanisms of fracture and as a tool for archaeological studies are discussed.     

Mapping Mesolithic and Neolithic cultures behaviours and interactions with nature and properties of rocks in Western France

Multivariate statistical methods are used to study recent Prehistory lithics from the Armorican Massif, allowing us to classify them in more or less distinct groups according to the structural and mineralogical qualities of rock types involved. Analyses are carried out on metamorphic, sedimentary and magmatic rocks making up lithics collected from 31 localities. The petrographic properties are determined by polarizing microscope (POM), while the mechanical properties are obtained by Vickers's indentation method (VI), compression/traction (CT) and ultrasound echography (UE). The results provide us with important information about the management of lithic raw materials used by various human and cultural groups during the Mesolithic and Neolithic of the Armorican Massif. The more commonly used materials show a homogeneous and stable distribution of regional technology styles. The rock types exhibiting mature and homogeneous structures possess the better qualities for knapping (fracture energy G_Ic) and use (edge toughness M₁), and are more involved in exchange. The application of Upward Hierarchical Classification (UHC) and Principal Component Analysis (PCA) allows us to identify the classes of materials as well as the causes of variations of rock type abundance within the lithic assemblages of the Mesolithic and the Neolithic. In this way, we can then also predict the discovery of archaeological artefacts in areas lacking any known indications of the exploitation of outcropping materials.     

“南澳Ⅰ号”出水陶瓷器脱盐技术对比研究

为了对“南澳Ⅰ号”明代沉船出水的大量陶瓷类文物进行安全高效的脱盐保护处理,选取“南澳Ⅰ号”出水的3种不同窑系的陶瓷文物作为研究对象,对其胎体理化性能进行分析检测与对比,并在常温静水浸泡、加热静水浸泡、超声波与加热-超声波4种方法11种不同技术参数下分别进行脱盐实验,并作对比研究。研究发现,加热与超声波技术相比常温浸泡法可以大幅度提高脱盐的速率,但是随着温度的继续升高与超声波频率的增加,脱盐速率增加幅度不大。实验中发现超声波对比较脆弱的陶瓷文物的釉面与胎体会产生一定影响。在对比实验基础上提出了3种不同窑系的陶瓷文物相应的最佳脱盐参数,以期为安全高效地完成“南澳Ⅰ号”出水的2万多件陶瓷器的保护脱盐提供研究支持,并为其他沉船陶瓷器保护提供借鉴。     

基于近红外高光谱技术的敦煌莫高窟壁画起甲病害风险评估方法

针对敦煌莫高窟壁画起甲病害的发生发展过程,本实验采取了近红外高光谱技术进行分析和评估。高光谱技术由于其非接触、光谱信息丰富能够无损地应用于壁画的病害检测上。首先通过高光谱成像系统采集不同起甲病害程度下的壁画高光谱图像,提取出壁画从未发生起甲到碎片脱落的病害周期内各个阶段对应的光谱信息,从而建立起甲病害光谱数据库;然后分别使用偏最小二乘回归(PLSR)、主成分分析与支持向量机、主成分分析与人工神经网络三种评估模型对此光谱数据库进行训练,并且通过平均误差、决定系数的大小决定评估模型的优劣。实验结果显示PLSR取得了较好的评估结果,同时利用PLSR评估模型中的加权回归系数得到光谱中的重要波段;之后运用PLSR评估模型对未标注风险情况的壁画进行逐像素点的病害风险评估,获得壁画的起甲风险评估图。实验结果显示基于近红外高光谱技术能够对敦煌壁画起甲病害进行风险评估。     

The Thermal History of Maize Kernels Determined By Electron Spin Resonance

Electron spin resonance (ESR) can be used to determine the thermal history of charred organic material. Maize seeds were heated under controlled conditions in order to produce calibration curves relating g‐values (the rate of electron splitting) and spin intensities (the number of spin centres) to heating temperatures, times and conditions. These experiments reproduced results that had been previously obtained by other laboratories, with some minor exceptions. The calibration curves were then used to reconstruct the thermal histories of charred maize kernels from several prehistoric sites in eastern North America. At these sites, the differing thermal histories of maize kernels are correlated with depositional contexts.     

COMPOSITIONAL VARIATIONS IN AGED AND HEATED PISTACIA RESIN FOUND IN LATE BRONZE AGE CANAANITE AMPHORAE AND BOWLS FROM AMARNA,EGYPT*

This study examines resinous deposits from the interior surfaces of sherds of imported Canaanite amphorae and locally produced bowls from the 18th Dynasty site of Tell el‐Amarna, Egypt. Archaeological evidence indicates that the Canaanite amphorae were used for resin transport, whilst the bowls are associated with burning resin as incense. A number of characteristic triterpenoids identify all the resinous deposits from both vessel types as Pistacia spp. No other resins were observed and there was no evidence of mixing with oils or fats. The composition of the archaeological resins is more complex than that of modern pistacia resin, due to degradation and generation of new components. Experimental heating alters the relative abundance of the triterpenoid composition of modern pistacia resin. One component, the triterpenoid 28‐norolean‐17‐en‐3‐one, is produced by such heating; however, an increase in its relative abundance in ancient samples is not matched by the archaeological evidence for heating. It is therefore not possible to use this component reliably to identify heated resin. However, additional unidentified components with a mass spectral base peak at m/z 453 have been associated with seven (out of 10) bowls and are not observed in resins associated with Canaanite amphorae. It is proposed that these components are more reliable molecular indicators of heating.     

Formation of Fluid Inclusions during Heat Treatment of Barremo‐Bedoulian Flint: Archaeometric Implications

At the end of the fifth millennium bc , the development of a specialized lithic industry in the Chassey societies of south‐eastern France and its dissemination as far as Catalonia and Tuscany attest to important socio‐economic changes in the Mediterranean Neolithic societies. The lithic production was made on barremo‐bedoulian flint that was heat‐treated to improve the sharpness of the tools produced. Microscopic observations of archaeological and geological, heated and unheated barremo‐bedoulian flint samples allowed us to highlight the heat‐induced formation of fluid inclusions. Microthermometry analyses showed that these inclusions contain pure H₂O, most probably resulting from the dehydration of length‐slow (LS) chalcedony and the closure of narrow pores, according to the model proposed by Schmidt et al. ( 2012 ). Our results enable us to estimate the heating temperatures used by Chassey artisans to ≈ 230°C. We also propose the ‘pressure cooker’ model to explain the migration of liquid water in flint nodules heated to 230°C. Then, we discuss the ability of a particular type of flint to be heat‐treated, and hence its value for Neolithic society, which depends on: (1) the amount of LS chalcedony that ensures the water release at relatively low temperature; and (2) on the total volume of porosity available to store the dehydration water.