Summary.-Five groups of rats were treated by inhalation for 12 months with the U.I.C.C. preparations of the 3 main commercially used asbestos types, chrysotile, crocidolite and amosite. The experiment was designed so that the effects of both fibre mass and fibre number could be examined. The results indicated that chrysotile dust caused far more lung fibrosis than either amphibole type even when the fibre numbers in the dust clouds were similar. All malignant pulmonary neoplasms found during this study occurred in animals treated with chrysotile. The fibre-number calculations used for the generation of dust clouds were evaluated using the parameters recommended by the Health and Safety Executive in 1976, by which all fibres over 5 ,um long are counted using a phase-contrast light microscope. When fibrelength distributions were calculated using a scanning electron microscope, however, it was found that the chrysotile clouds used in this study contained many more fibres over 20 ,um long than either of the amphibole clouds. The results, therefore, support previous suggestions that long asbestos fibres are more dangerous than short. They also indicate that neither a single mass standard, nor the present fibre-number standards are satisfactory.
Elevated concentrations of P2O5 of 2–12 wt% absolute were observed in the matrices of a small group of ceramics with the electron microprobe. P2O5, CaO and FeOt are enriched towards the surfaces in some cases and elemental correlations suggest precipitation of a crystalline calcium phosphate with a stoichiometry close to CaO · P2O5. Scanning electron microscopy with X‐ray mapping showed P2O5 to be dispersed in the ceramic matrix on a very fine scale, while X‐ray diffraction detected no crystalline phosphate. Parallels are drawn with the precipitation of phosphate in the surfaces of weathered glass. It is concluded that the amorphous phases produced on firing behave as chemically active substrates which facilitate the adsorption or precipitation of very fine grained calcium phosphate from the burial environment.
The modern analytical SEM, which can provide high-quality imaging facilities together with quantitative elemental analysis using an energy-dispersive spectrometer, is finding wide application in the investigation of archaeological problems. Many of these investigations involve the study of silicate and carbonate-based artefacts which may be relatively unmodified from their original geological parent raw materials so that mineralogically based interpretations are often appropriate. In this paper we present a series of examples illustrating the role of the analytical SEM in the mineralogical investigation of archaeological problems, including the characterization and provenancing of geological raw materials, the elucidation of the processes used to transform those raw materials into useful objects and the recognition and characterization of changes which archaeological artefacts may have undergone during burial or during storage.
The determination of the sources of ancient ceramics by the identification of diagnostic mineral inclusions in thin section is an approach which has produced some impressive results (see Williams 1983 for a recent review). However, many regions are characterised by geological successions which are monotonous on a scale of hundreds or even thousands of kilometers; hence the mineralogies of ceramics from distant production centres may appear very similar. In such cases, variation in the size, shape and proportion of non-plastic inclusions, rather than their composition, may allow characterisation and discrimination of the products of different kilns. Such an approach, commonly termed 'textural analysis', is being increasingly applied, and the reader is referred to the reviews of Darvill and Timby (1982) and Streeten (1982) for examples and discussion.The techniques used in textural analysis have been in large part adopted from those used by sedimentary petrologists (e.g. Folk and Ward 1957, Pettijohn 1949, cf. Peacock 1971. Most studies have concentrated on the use of size rather than shape or proportion of inclusions, producing a body of data, the 'grain-size distribution' which is amenable to statistical analysis and manipulation (Darvill and Timby 1982, Leese 1983). In order to obtain a grain-size distribution, between 50 and 200 grains (cf. Betts 1982, Wandibba 1982) in a thin section are measured, usually using an eyepiece graticule in a petrological microscope. These measurements are time-consuming, tedious and tiring for the operator and accuracy and precision are likely to depend on a strong subjective element. For these reasons we are experimenting with a semiautomatic image analyser, which promises to make measurements easier, more accurate and allows a much wider range of textural characteristics to be determined. The present paper presents the results of preliminary experiments designed to determine the effect of sampling procedure on the observed grain-size distribution. These have broader implications for the methods adopted in other studies. M 1ZT H 0 D SThe Kontron MOP-Videoplan image analyser interfaces a petrological microscope with a TV monitor, microcomputer and digitizing tablet. Individual grains from the field of view are outlined on the digitizing tablet with a pen which moves a cursor on the TV screen and selected size and shape parameters for each grain are calculated by the measuring programme and stored on magnetic disc for further statistical evaluation, if required.A 'standard image' (SI), based on a thin section of sand-tempered pottery, was produced which could be analysed repeatedly using different grain selection procedures. The outlines of 64
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