Neutron tomography for the assessment of consolidant impregnation efficiency in Portuguese glazed tiles (16th and 18th centuries)

摘要

Neutron tomography (NT) has been applied to visualize the inner structure of ancient Portuguese glazed tiles undergoing conservation treatments. Neutrons have the advantage of interacting strongly with hydrogen, so NT is able to map hydrogenous compounds with high sensitivity. The present study explores its potential for assessing the distribution of the consolidant Paraloid B-72 inside tiles, to evaluate the efficiency of two different methods of treatment: brushing and immersion in solution. Using a prototype NT setup at the Reactor Português de Investiga??o (Sacavém, Portugal), each two-dimensional image is obtained from a 90 s exposure, at a thermal neutron flux of 2× 10~5n cm~(-2) s~(-1) at the irradiation site. The neutron beam has a diameter of 5 cm, so fragments with outer dimensions upto 4.8 cm can be inspected. Samples are automatically rotated by an angle of 0.9-between successiveimages. Images were obtained before and after the application of the consolidant. The results obtainedshow that: (i) NT is a useful tool for visualization of the inner structure of ancient glazed tiles, and toassess penetration depth of consolidant and its distribution inside the tile; and (ii) brushing with 10%Paraloid- B-72 in acetone solution appears to be more efficient than immersion. Neutron tomographyshowed a greater and more uniform retention of resin inside the tile if the brush is used to apply theconsolidant, to increase the cohesion of the object.