Maintaining marble monuments


Scientists in Italy have made a new oxamate salt that could help shield monuments from weathering.

‘Set in stone’ describes something permanent or difficult to change. However, in regions of polluted air, this begins to lose meaning. Sulfur and nitrogen oxides produce acid rain, which dissolves calcite in limestone and marble monuments, and leads to their degradation.

The treatment was tested on marble statues by Giuseppe Maria Sartorio in the Monumental Cemetery of Bonaria in Cagliari, Sardinia © Paola Meloni

To tackle this problem, scientists lead by Massimiliano Arca at the University of Cagliari, have synthesised a promising protective agent for calcerous stone. Calcium carbonate reacts with oxamate ions to produce a calcium oxalate salt. To allow appreciable salt formation on marble and limestone surfaces, the team increased the oxamate ions’ solubility by adding a phenyl group and creating ammonium N-phenyloxamate. After immersion in the ionic solution, FT-NIR spectra and SEM microscopy uncovered an invisible, low solubility, crystalline calcium phenyloxamate coating. With no visible colour change and a thickness of up to 15µm, this salt is an ideal candidate to prevent weathering and retain the appearance of stone monuments.

References

L Maiore et al, New J. Chem., 2016, DOI: 10.1039/c5nj02505b


Related Content

Potash on a megascale

11 March 2016 Premium contentFeature

news image

A new mine could produce up to 20 million tonnes of potash each year and provide 1000 jobs – but it’s in a national park....

Taj Mahal browning due to light-absorbing particles

13 January 2015 Research

news image

Researchers have identified the pollutants behind the marble monument’s gradual colour change

Most Commented

New antibiotic picked from nose bacteria

27 July 2016 Research

news image

Discovery suggests human microbiome may be an untapped source of antimicrobial compounds

Perovskite boosts silicon solar cell efficiency

25 November 2015 News and Analysis

news image

Silicon industry will be ‘beating a path to the door’ of inventors, says scientist