UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2011 Meeting


Section: Atomic and Molecular Physics; Astrophysics


Title:
Investigations of Colour Defects Induced by Gamma Irradiation in Paintings


Authors:
C.D.Negut(1,2), V.Bercu(1), and O.G. Duliu(1)


Affiliation:
(1) University of Bucharest, Department of Atomic and Nuclear Physics,P.O. Box MG-11, 077125 Magurele - Ilfov, Romania

(2) Horia Hulubei National Institute for Physics and Nuclear Engineering, P.O. Box MG-6, 077125 Magurele - Ilfov, Romania


E-mail
dnegut@nipne.ro


Keywords:
decontamination, gamma irradiation, painting, historical pigments, EPR, colorimetry


Abstract:
Biocide effect of ionizing radiation was put into evidence soon after the discovery of X-rays and radioactivity in 1895-1896. The first patent regarding the use of ionizing radiation to preserve food was issued in 1905. Presently, processes such as food irradiation or radiation sterilization of medical products are well established technologies. Gamma irradiation can be used in decontamination of art objects as well. Despite of its advantages when compared with classic methods, decontamination by gamma irradiation is still an exotic method. Conservators’ restraint in using this method is caused not only by the negative connotation of “radiation” but also by the fact that few papers describe the effect of irradiation on the properties of materials which compose art objects. The aim of this paper is to investigate colour defects induced by gamma irradiation in materials used in paintings. From this point of view the most important material in a painting is the pigment. As these pigments retain their crystal structure after mixing with binders, the main defects induced by gamma irradiation can be colour centres. The study is focused especially on historical white pigments which are the most susceptible to accommodate colour centres and thus suffering colour changes. The presence of colour centres is investigated by reflectance spectroscopy. The contribution of these irradiation defects to the colour of pigments is evaluated using CIELAB colour. Most of colour centres are paramagnetic therefore EPR spectroscopy is also used to confirm the hypothesis of colour centres formation during irradiation. Also we present the results of colour tests on samples simulating oil paintings and wooden icons from XVIII-XIX.