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Evaluating the effectiveness of calcium hydroxide nanoparticle dispersions for the consolidation of painted earthen architectural surfaces

  • Author(s): Lohnas, Dawn Elise
  • Advisor(s): Kakoulli, Ioanna
  • et al.

This paper describes a laboratory evaluation of the effectiveness of a calcium hydroxide nanoparticle dispersion (CaLoSiL) in consolidating manufactured adobe blocks with painted clay surfaces. The particular challenges faced in the conservation of painted earthen surfaces are discussed. Additionally, a review of past consolidation efforts and the properties of consolidants typically used in the treatment of wall paintings is given, with a particular emphasis on inorganic mineral treatments. For this study, test blocks were created based upon the description of Moche painted adobe surfaces in the literature. Blocks were plastered with a clay plaster layer, which included a cactus-mucilage extract as a binder. After the plaster layer had been artifically aged using cycles of fluctuating heat and relative humidity, a painted clay layer was added which consisted of a mixture of kaolin and charcoal. The consolidant (CaLoSiL) was applied to the block surfaces via spraying, and allowed to set for three weeks. Surface absorption tests, pH tests, the Scotch Tape test (ASTM D4214-07), X-Ray Diffraction (XRD) and Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) were used to examine any physical or chemical changes in the blocks. Microscopy, photography, and Munsell Color Charts were used to evaluate visual differences before and after consolidation. Cross-sections taken before and after consolidaiton were examined using digital microscopy and Scanning Electron Microscopy (SEM). Overall, the samples showed some whitening following consolidation, but also an improvement in cohesion of the paint layers. While the microscopy results were somewhat inconclusive, XRD revealed the presence of a calcium silicate hydrate (plombierite) on paint layers from the treated samples. Suggestions for future studies which might incorporate additional variables and testing techniques are given.

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