Françoise Bechtel

Changes in luminescence properties induced by thermal treatments; a case study at Sipan and Trujillo Moche sites (Peru)

Abstract TL-dating studies were carried out on prehispanic pottery attributed to the Moche culture of Peru (from BC 200 to AD 800 according to the previously known chronology). A greater than expected scatter in ages was found for samples known, from archaeological considerations, to have been contemporaneous. This was related to applying a fixed, but inappropriate, annealing temperature to the grains prior to their irradiation to regenerate the TL growth curve. The dependence of growth of TL and equivalent dose evaluation on this annealing temperature was tested in the range 400–1000°C. A combined cathodoluminescence/TL study was used to select the appropriate thermal treatment for evaluation of the final equivalent dose. This procedure, which we suggest can be generally applied in pottery dating, resulted in a reduction of age dispersion when applied to groups of contemporaneous ceramics.

Gilding Techniques in Mural Paintings: Three Examples from the Romanesque Period in France

Since paleo-Christian times, gold maintains a close relationship with colour within the church. However, more than just colour, gold is also matter and light. It is heat, weight and density. The use of the precious metal has an artistic, aesthetic, political and liturgical function: it is a sign, mark, and symbol of power and authority.

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.

An Investigation into the Ceramic Technology of the Two-Colour Tiles of “Prince Noir” Castle (Bordeaux, France, Thirteen to Fourteenth Centuries AD)

Two-colour tiles were produced in abundance in France and England during the thirteenth and fourteenth centuries AD. They replaced the mosaic, hand-incised and counter-relief tiles that had been developed since the twelfth century. These tiles proved very successful and many regional styles of decoration for religious and secular opulent edifices. Two-colour tiles are usually made by applying a pattern impression on an unfired, clayey tile. The impression is then filled with a slip, and, finally, the surface is covered with glaze.