The use of micro-XRD for the study of glaze color decorations

The compounds responsible for the colours and decorations in glass and glazed ceramics include: colouring agents (transition metal ions), pigments (micro-and nano-precipitates of compounds that either do not dissolve or recrystallize in the glassy matrix) and opacifiers (microcrystalline compounds with high light scattering capability). Their composition, structure and range of stability are highly dependent not only on the composition but also on the procedures followed to obtain them. Chemical composition of the colorants and crystallites may be obtained by means of SEM-EDX and WDX. Synchrotron Radiation micro-X-ray Diffraction has a small beam size adequate (10 to 50 microns footprint size) to obtain the structural information of crystalline compounds and high brilliance, optimal for determining the crystallites even when present in low amounts. In addition, in glass decorations the crystallites often appear forming thin layers (from 10 to 100 micrometers thick) and they show a depth dependent composition and crystal structure. Their nature and distribution across the glass/glazes decorations gives direct information on the technology of production and stability and may be related to the color and appearance. A selection of glass and glaze coloring agents and decorations are studied by means of SR-micro- XRD and SEM-EDX including: manganese brown, antimony yellow, red copper lusters and cobalt blue. The selection includes Medieval (Islamic, and Hispano Moresque) and renaissance tin glazed ceramics from the 10th to the 17th century AD

MÖSSBAUER STUDIES ON THE NATURE OF THE RED OR BLACK GLAZES ON GREEK AND INDIAN PAINTED WARE

La spectroscopie Mössbauer et la microscopie électronique à balayage (SEM) ont été utilisées pour étudier divers échantillons protégés par un revêtement. En utilisant la diffusion des rayons X (Mössbauer), on a montré que la partie brillante rouge et noire des échantillons de la Grèce Attique contenaient respectivement de la magnétite et de l'haematite, tandis que le coeur ne contient que l'haematite. Les mesures par SEM montrent que la partie brillante a une épaisseur de 30 µm et est totalement vitrifiée. Pour les objets 'Samien' on a relevé la présence d'haématite à la fois dans la partie brillante rouge et dans le coeur de l'échantillon. L'épaisseur du verni noir des objets polis du Nord de l'Inde' (NBPW) est environ 10 µm mais ni le verni ni le coeur ne sont vitrifiés, ce qui indique une plus faible température de cuisson. Le spectre de diffusion d'électrons effectué sur le verni (NBPW) fait apparaître un doublet d'une structure ferrique bien que l'un des échantillons donne un spectre contenant une composante magnétite, le coeur contient du fer dans une structure de silicate. Les résultats sont discutés dans le but de comprendre les techniques de fabrication utilisées.Mössbauer spectroscopy and scanning electron microscopy (SEM) has been used to study samples of various types of painted ware. Using Mössbauer X ray scattering, the black and red gloss on samples of Greek Attic ware are shown to contain respectively magnetite and haematite, while the core contains haematite. SEM analysis shows that the gloss has a thickness of ≈ 30 µms and is totally vitrified. Both the red gloss and core of Samian ware contain haematite. The gloss thickness on Indian Northern Black polished ware is found to be ≈ 10 µms while both the gloss and core exhibit no vitrification indicating a lower firing temperature. Mössbauer electron scattering spectra for the gloss consist of a ferric doublet although one sample gives a spectrum containing a magnetite component, while the core contains iron in a silicate structure. These results are discussed in terms of the suggested techniques for manufacture