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Marble conservation to be improved with new research

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Science & Technology, Australia (Commonwealth Union) – The splendor and beauty of marble has made it a popular option for palaces and monuments, going back centuries, in fact the very word marble is derived from the Greek language for shining stone. Marble is also available in a variety of colors such as pink, grey, black, brown, green, red, and white however white remains the most popular option that is presently used.

A new study has demonstrated how chemistry researchers combined computational modelling and experimental methods to gain knowledge on how various additives enhance protective treatments.

Researchers applied a novel approach that may enhance how artefacts created from marble are preserved.

The findings were published in Applied Surface Science, where researchers from the University of New South Wales (UNSW) and The University of Bologna in Italy combined computational modelling with experimental procedures to measure if various organic solvents such as alcohol may enhance a protective treatment applied in marble preservation. Researchers discovered that even though a range of solvents acted differently on the marble surface, all enhanced the treatment in a similar manner.

The utilization of marble in a variety artefacts of cultural significance across the globe, with examples such as the statue of David by Michelangelo in Florence to the famous columns of the Parthenon in Athens demonstrates that their preservation is vital for future generations as when marble is exposed outdoors, they are vulnerable to deterioration from the rain.

“Most of us are familiar with some iconic marble works of great historical and cultural significance. We’re working to find ways to help preserve these works for future generations so they can have the chance to enjoy and appreciate them just like us,” explained Dr Martina Lessio, who is a lecturer in the School of Chemistry at UNSW Science as well as a senior author of the study.

Recently, a significant new treatment has been formed by conservation scientists to enhance marble resistance to rain. This treatment is successful when forming a durable protective coating on the marble surface composed of calcium phosphate (CaP), or hydroxyapatite, which is a naturally occurring mineral also present in teeth and bones. In comparison to other treatments, it leads to no discoloration or aesthetic alterations to the marble.

Prior studies indicated that adding organic solvents like alcohol to this treatment assists in enhancing the ability of the hydroxyapatite layer to protect the marble, but the reasons for the observed enhancement were not very well known.

“Finding out the reason it’s behaving this way is critical to be able to select the best possible solvent for the treatment and maximise the protective efficacy,” Dr Lessio says.

“Computational tools allow us to investigate the fundamental chemistry behind these observations.

“Combined with experimental insights, we can better understand how these organic solvents work at the molecular level and develop a rational design for the marble conservation treatment.”

The research was conducted with the testing of the adsorption of ethanol, isopropanol as well as acetone on the calcite surface of a Carrara marble sample, which is a type of marble common in sculpture and architecture.

To gauge suitability, initial simulations of the interaction between the various solvents and the calcite surface of the marble was conducted applying computer modelling. The experiments, involved testing 4 different conditions, with 1 utilizing just water as a solvent and the remaining 3 utilizing the additives. The marble samples were treated with immersion in different beakers with 100 mL of an aqueous solution of a phosphate precursor, with and having no organic additives.

The various organic solvents displayed different behaviors when they approached the marble surface with the models. The alcohols made a water-repellent layer on calcite, as the acetone produced a mixed, dynamic layer. However, each solvent enhanced the protective performance of the treatment with no key differences between them in the experiment.

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