The transformations induced in two clays differing in Ca content, by firing under reduced conditions up to 1080°C, were studied by X‐ray diffraction, scanning electron microscopy, Mossbauer, and magnetization measurements. In the calcareous clay, gehlenite forms at lower temperatures (900°C) and, in addition, wollastonite forms at higher temperatures (1080°C). Ferric iron persists even under strongly reducing conditions and its presence is attributed to trapping in gehlenite. Extensive vitrification is observed in the non‐calcareous clays. Ferrous iron, produced by dissociation of iron oxides, is partly dissolved into the vitreous matrix and partly incorporated into the spinel mineral hercynite. The key role of Ca in controlling the above transformations was verified by studying the clays after removal or addition of calcite. The interaction of Ca with the clay constituents and its progressive attack on the quartz grains forming wollastonite zones was observed with the electron microscope. The bulk magnetic properties of the samples depended principally on the amount of iron oxides present, which in turn were strongly affected by firing temperature and type of clay. Metallic iron was detected in strongly reducing atmospheres.

Studies of the average crystal structure properties of human dental apatite as a function of age in the range of 5–87 years are reported. The crystallinity of the dental hydroxyapatite decreases with the age. The a-lattice constant that is associated with the carbonate content in carbonate apatite decreases with age in a systematic way, whereas the c-lattice constant does not change significantly. Thermogravimetric measurements demonstrate an increase of the carbonate content with the age. FTIR spectroscopy reveals both B and A-type carbonate substitutions with the B-type greater than the A-type substitution by a factor up to ~5. An increase of the carbonate content as a function of age can be deduced from the ratio of the ν 2CO3 to the ν 1PO4 IR modes.

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Wall paintings spanning two millennia of Cretan painting history and technology were analysed in an effort to determine similarities and evolutions of painting materials and technology. A multi-technique approach was employed that combined the use of a) laser-induced breakdown spectroscopy (LIBS) and Raman microspectroscopy, based on mobile instrumentation, appropriate for rapid, routine-level object characterization, and b) non-destructive x-ray diffractometry (XRD), performed directly on the wall painting fragment, that provides detailed information on the minerals constituting the paint. Elemental analysis data obtained through LIBS were compared to molecular and crystal structure information featured by Raman spectroscopy and XRD. Cross-sections from selected samples were also investigated by means of optical microscopy and scanning electron microscopy coupled to microprobe analysis and x-ray mapping that enabled identification of several mineral components of the paint confirming the results of the XRD analysis. In parallel, replica wall paintings, created with known pigments and binding media, for reference purposes; were examined with optical microscopy and stain tested for organic materials. The overall study shows that the LIBS and Raman techniques offer key advantages, such as instrument mobility and speed of data collection and interpretation that are particularly important when dealing with on site investigations. Thus they are capable of providing important compositional information in an effective manner that enables quick surveying of wall paintings and permit targeted sample selection for further analysis by advanced laboratory techniques. The present multi-analytical technique study is part of a broader project that aims to explore the wall painting pigments used on the island of Crete from the Bronze Age to the Roman and Byzantine periods. A fairly large body of work exists on the analysis of pigments used in Bronze Age wall paintings from Crete [9,10,11] in relation to issues concerning on the one hand painting materials and technology and on the other painting style and thematic content. In contrast, information regarding wall paintings from later periods is scarce. The current project begins to redress the balance, and to augment our understanding of the whole palette of Cretan wall painting pigments. Keywords: archaeological pigments, wall paintings, analysis, LIBS, Raman, XRD, SEM-EDXThe principal materials and methods of constructing a wall painting remained almost unchanged onCrete from the Bronze Age until (and in many cases including) the 20 th century. Levelling layers of plaster, usually a combination of hydrated lime (calcium hydroxide) with various inorganic and organic filler materials such as calcitic or quartzitic sand, crushed ceramics, or straw, were applied to the wall, prior to the application of a thin, fine layer of almost pure slaked lime. In most cases, pigments were ground to powder, mixed with water, and applied to the still wet uppermost plaster

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A systematic behavior in the crystal structure parameters of natural, synthetic, carbonate, and non-carbonate apatite is revealed from Rietveld refinements of neutron powder diffraction experiments. The results of this work on synthetic carbonate hydroxyapatites (CHAps) are consistent with the mechanism of carbonate substitution on the mirror plane of the phosphate tetrahedron, as it was introduced for the natural carbonate fluorapatite (CFAp). The present comparison shows that the tetrahedral bond lengths P–O1 and P–O2 decrease by 3–4% in all carbonate apatites. The atomic displacement parameters (ADPs) of the tetrahedral (T) and the O3 sites are greater in the carbonate than in the non-carbonate apatites. The atomic positional disorder of the T site (P/C site) is greater in the CFAp than in the CHAps, while the opposite happens at the O3 sites. Finally, the room-temperature ADPs of all of the atoms in the CFAp and CHAps show the same behavior as in the corresponding non-carbonate materials.

Atomic positional disorder of a single-phase natural carbonate fluorapatite (francolite) is revealed from analysis of the atomic displacement parameters (ADPs) refined from neutron powder diffraction data as a function of temperature and carbonate content. The ADPs of the francolite show a strong disturbance at the P, O3, and F sites. When it is heat treated to partially or completely remove the carbonate, the ADPs as well as the other structural parameters resemble those of a fluorapatite (Harding pegmatite) that was measured under the same conditions. The various structural changes are consistent with a substitution mechanism whereby the planar carbonate group replaces a phosphate group and lies on the mirror plane of the apatite structure.