M. Járó - L. Költő szerk.: Archaeometrical research in Hungary (Budapest, 1988)

Dating - ERDÉLYI Balázs: Thermoluminescence dating in the history of arcmtecture

In occurrence of style critically interprétable details, periodization and relative chronology are generally unimpeded. That is, different style periods of the building can be delimited, even intervals within style periods can be determined, but no exact chronometry data can be obtained. This result is seldom convenient for the actual goals of research, at most it is acceptable if integrated by exact written documents. Even if rarely, such cases do occur in the history of architecture - mostly for late mediaeval and modern buildings. Mediaeval written documents often refer to buildings but most of the data permit chronological dating only "ante quam", or sometimes, "post quam". 2. Thermoluminescence dating The endeavour to develop exact dating methods for historical building materials and structures is an old problem of the archaeological investigation of monuments. Such methods are of outstanding significance for investigating monuments with accessory archaeological finds, written documents, or style critically évaluable details. The testing of building materials primarily had recourse to physical dating methods, relying on the decomposition of radiactive isotopes, the direction and intensity variations of the Earth's magnetic field, and on time independent chemical changes after being made and eventually buried. Among them I feel the most important, the most promising procedure to be thermoluminescence dating. The TL method relies on the effect of very intensive energy radiation, emitted as a product of decomposition of radioactive impurities in clay. Thermoluminescence consists essentially of the previously irradiated crystal absorbing the exciting energy, it stores a part of it for a long time (in a quantity linearly related to time), then, upon heating, it is emitted as luminescent photons. This mechanism can be understood from the band theory solids (Becker, 1973). In the course of history, man-made clay artifacts (vessels, decorative and utility ceramics, building units) have been fired to increase durability. At the firing temperature the geological information became cancelled, i. e., the "archaeological clock" started from zero. Provided subsequently the clay object was not exposed to significant heat shocks (t = 200 °C), after a time the TL signal of the clay specimen will be proportional to the time after being made. The application of the TL method in the history of architecture is expected: - to date buildings with brick or mixed masonry of unknown age; - to distinguish construction phases within a building. In evaluating the results, let us recall that: a) results yield the time elapsed since the bricks were fired, rather than the actual building time. Bricks from pre-existent buildings might be utilized, or later repairs might be made using new bricks; b) data always refer to a group of bricks rather than to the entire building; c) error limits (standard deviation of the mean age, or context error) have to be reckoned with; d) not every brick can be TL dated. The TL method is advantageous in that the dated event is actually brick firing, and by its direct relation to ceramics essential for traditional archaeological chronology. TL dating as a method belongs to the same category as the periodization traditionally applied for dating in the history of architecture. Their parallel use may support or refute style critical findings. It is of use in cases where there are no style marks at all, or those fitting narrow intervals, such as maybe the unique possibility of dating.