PLASTER CASTS AND CORROSION AN EXPERIMENTAL STUDY ON REMOVAL OF CORROSION PRODUCTS FROM PLASTER CASTS

Abstract: Conservation of plaster casts is complex due to the nature of the material itself. Corrosion of armature and metal structural supports is one of the most common causes of damage in plaster casts and subsequent corrosion staining. This study examines the use and efficiency of different cleaning systems in removing corrosion staining from plaster casts. Three different carriers were employed - commercial grade liquid latex, Arbocel® and xanthan gel - all in combination with varying concentrations of chelating agent EDTA. Evaluation of efficiency was based on ease of use, removal of corrosion products and damage to the plaster substrate. A combination of colorimetry, visual examination and documentation, microscopy and XRF analysis was used to evaluate results. Results of this study demonstrate that corrosion staining in plaster casts can be treated efficiently with xanthan gels and Arbocel® poultices, albeit some original material may be removed in the process. The influence of prior cleaning and condition of the plaster object itself proved highly relevant. Latex cleaning systems proved unreliable and difficult to control on break edge surfaces; systems left residue and overall removed an excessive amount of original material. Arbocel® systems indicated the most potential; comparatively less damage to the plaster substrate and efficient removal of corrosion products. It is further concluded that a combination of XRF and microscopy as a means of evaluating cleaning systems provided more supplementary data than colorimetry values - due to the surface stratigraphy of the experimental material and uneven severity of corrosion staining, reliable values were difficult to obtain. Furthermore, results of this study strongly suggest that surface stratigraphy, substrate condition and extent of staining is highly relevant when choosing a carrier for delivering cleaning agents.