LONDON.- As the National Gallery prepares to celebrate its 200th anniversary, it’s no surprise that such a big birthday has required some cosmetic work.

Over the last three years the external façade overlooking Trafalgar Square has undergone a phased major clean and refurbishment programme, made possible by the generous support from the late Julia Rausing and her husband Hans Rausing. The philanthropic couple offered to help the Gallery mark its Bicentenary this year. With the final scaffolding down, the stone looks as fresh and clean as it did when the young National Gallery formally opened to the public in 1838.

A slightly bigger task than the average domestic spring clean, the front of the building is clad in Portland stone – a relatively soft and porous natural material mined from Portland Bill, the southernmost point of Dorset. The challenge for conservation specialists Paye Stonework and Restoration was to clean the building but without removing the patina of age, while conserving as much as possible of the original elements.

Julia and Hans Rausing have been long standing supporters of the Gallery. In fact, it was the late Julia Rausing who approached the Gallery with the idea of refurbishing the façade in 2019. The façade was last refurbished in the early 1980s. Being located in central London, the Museum exterior is impacted from air pollution and the urban environment.

All areas have been cleaned with a combination of dry cleaning, super-heated water cleaning, and mild abrasive water based cleaning techniques. Areas with stubborn and dark staining then had a poultice applied to draw out the pollutants; followed by a final wash down to remove remaining dust or debris.

• Dry cleaning is carried out with stiff bristle brushes.

• Super-heated water cleaning is carried out using a Thermatech steam generator machine providing pressured water at 145oC to soften and remove dirt from the stone.

• Gentle abrasive cleaning is carried out using the TORC system, which uses a mix of water and fine, powdered calcium carbonate combined with pressure to pass through a nozzle that creates a swirling, vortex motion that removes stubborn dirt without damaging the stone.

• Poultice cleaning softens and removes residual sulphate crust. It also draws out contaminants from within the pores of the stone.

In some cases, cleaning also made clear the need for repairs, in places where the watertightness of the façade was either already compromised, or if left, would have made the stone at risk of further damage. Unless strictly necessary, missing stone parts were not rebuilt and replaced.

Gabriele Finaldi, Director of the National Gallery, said, ‘The National Gallery façade on Trafalgar Square is one of London’s most recognizable sights. Julia Rausing encouraged us to undertake the complex task of cleaning and restoring it for the Gallery’s Bicentenary year. We are enormously grateful for Julia and Hans' support and are now immensely proud of our gleaming, elegant façade.’