20 March 2009

removing graffiti

This week, three of our conservators have been working on a contemporary sculpture located on the idyllic shores of Sydney Harbour. A wonderful setting; but the work was rather less inspiring.

One of the major challenges we face in the conservation of public art is dealing with human impact on the artwork. And of course, graffiti epitomises the negative impact that comes from some members of our society.

Graffiti removal is almost always problematic. Often, the marker (paint or pen) penetrates the pores or surface roughness of the materials used for the sculpture, and cannot be easily removed. At other times, the process required to remove the graffiti causes damage to the substrate. And occasionally, on sculptures like Dual Nature by Nigel Helyer, the graffiti can actually alter the characteristics of the material itself.

Weathering steel (of which "Cor-Ten" is the most well-known type) is a particular type of steel that corrodes slowly on exposure, giving a uniform rusty brown finish. The most prominent use of this material in Sydney is the shaft of Sydney Tower.

The impact of graffiti on weathering steel is quite substantial.

Firstly, once the graffiti is applied, it slows the rate of corrosion in the areas beneath the graffiti. So that when the graffiti is eventually removed, even if it is completely removed, the surface will be visibly different because of the varying rates of corrosion.

Secondly, even with very careful solvent dissolution of the graffiti, some rubbing or abrasion of the surface of the weathering steel is inevitable, and hence the surface corrosion layer is lost, resulting in a visible difference.

At "Dual Nature", our team of conservators decided that given the age of some of the graffiti (several years) and the highly visible shadows from removal of graffiti in the past, we would scrub back the surface layer of corrosion across the entire face of the sculpture in order to minimise the visible difference between areas that had been attacked with graffiti, and those which had not.

This meant that after carefully removing the graffiti, our conservators spent many hours scrubbing the surface of these wonderful shell elements.

Given the highly exposed location, the salt-laden air will accelerate the process of corrosion, or weathering, of the Corten steel, so that the surface layer of corrosion will redevelop quite rapidly over the coming months.
David West

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