engleski

The use of the IRB nuclear microprobe in a conservation process studies of a church portal

The southern portal of the St. Marco church in Zagreb, Croatia, which originates from late 14th or beginning of 15th century, is currently under the process of conservation. It is placed in a niche and protected from direct influence of the rainfall, but not from the influences of wind driven rain, fog, temperature variations and atmospheric pollution. The conservation treatments on calcareous sandstone consist of (i) removal of harmful sulphates (gypsum) from the surface of the material by saturated solution of ammonium carbonate ; and (ii) treatment of the material surface with the 10% solution of barium hydroxide in order to convert the remaining dissolvable sulphates into undissolvable (unharmful) compounds and to strengthen the material surface. The nuclear microprobe has been successfully used to demonstrate the level of the gypsum induced damage, and quality of conservation. More specifically, the surface quantity and depth concentration profiles of sulphur have been determined from a number of samples taken from the portal before and after the treatment with the solution of ammonium carbonate. To test the quality of treatment by the barium hydroxide solution, the depth concentration of barium in the samples of the material has been determined after the treatment. Both sulphur and barium concentration levels have been determined by scanning the proton beam over the samples, detecting PIXE spectra and creating elemental distribution maps.

conservation; nuclear microprobe

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