Max Schvoerer

Double Nanoparticle Layer in a 12th Century Lustreware Decoration: Accident or Technological Mastery?

Metallic lustre decorations of glazed ceramics, which appeared in Mesopotamia during the 9th century AD, can be considered nowadays as an historical example of controlled nanotechnology for optical devices. Their surprising optical properties are directly due to metallic nanoparticles that Islamic potters were able to bury in the first layers of glaze through empirical chemical means. Lustre technology is fascinating and many papers have been devoted to this subject. Many lustre samples have been investigated with the most modern equipment such as the synchrotron radiation, electron microscopy, micro-Raman spectroscopy and other spectroscopic methods. This decor made in the twelfth century during the Fatimid dynasty shows a quasi-perfect double layer of nanoparticles confirming the high technological mastery of this civilization. Moreover, up to now, no lustre has been found with an organization of nanoparticles as elaborate as the decor presented here.

Luminescence dating of burnt materials: effects of preheat treatment on OSL and consequences for dating procedures

For dating purposes, OSL experiments were carried out on a variety of silicate materials extracted from ceramics and kiln fragments which were already dated by TL. In order to check the thermal stability of signals, a study of the variation of OSL with preheat temperature showed, in a majority of cases, that OSL, recorded at room temperature, increases above 200°C before the normal thermal drainage at higher temperature, at more than 250°C. According to our data, preheat treatments at a temperature which induces an increase of OSL, lead to underestimated measures of equivalent doses (ED). So, dating protocols avoiding sensitivity changes by preheating have been carried out, using the more appropriate conditions of preheat and stimulation that get rid of unstable components, determined by preliminary studies. A good agreement between OSL and TL results is then obtained when no change in sensitivity occurs during the irradiation/optical bleaching cycles performed in ED measurements.

Gamma-thermoluminescence dating (Г-TL)—III: Checking the homogeneity of the structure by γ spectrometry☆

Abstract The experimental simplification of the TL dating method is one of the CRIAA Laboratory research fields in physics applied to archaeology. For radiochemical homogenous systems, Г-TL allows a significant simplification for the measurement of the natural dose-rate I while preserving an accuracy as good as the one of classical TL dating within certain limiting circumstances. For instance, in the case of large heated structures determination of I reduces to Iγ on site measurement (gammametry or dosimetry) and to k (α efficiency coefficient) determination. The annual dose-rate is then given by I=Г(k) I γ with Г(k)=12.17k+2.72 . However, it is necessary to test the hypothesis that radioactivity in the structure is homogeneous. For this purpose high resolution γ spectrometry is used as a routine laboratory technique applied to several similar samples (identical masses and shapes) of structure. The comparison between the natural γ-ray spectra (γ-rays of K40 and of U238 and Th232 radioactive series) allows establishment of applicability criteria for the Г-TL method, since for constant conditions, γ-ray intensities must be identical from one sample to another (to within statistical errors). We are now investigating structures of known age in order to find within what limits (in the radioactivity differences) the Г-TL can be used.