Dame Barbara Hepworth
'Four-Square (Walk Through)' 1966

For this project, Patina's sculpture conservation team collaborated closely with Tate’s conservators to carry out the treatment. The appearance of ‘Four-Square (Walk Through)’ had altered considerably since it was first installed. This was largely due to weathering in a coastal environment, but also because the artwork is more difficult to maintain on a regular basis because of the need for scaffolding to gain full access.

Early photographs of the sculpture seemed to show that the flat vertical faces were originally patinated with several different and contrasting colours. This included brown, several shades of green and possibly a white or very pale green. The images also showed that the rings piercing the square stacked elements were once polished and lacquered so the Hepworth Estate wanted to explore the possibility of restoring the rings as part of the treatment. However, they were concerned that if the rings were returned to their original polished appearance then they might sit slightly uncomfortably with the weathered patina of the rest of the sculpture. The aim was therefore to strive for a slightly toned-down polished finish in order to achieve a more integrated overall appearance. 

For this treatment we chose to use the ThermaTech heated pressure washer, which works with variable water pressure and temperature to remove surface soils as well as built-up waxes. We carried out a number of cleaning tests on different faces of the sculpture, varying the parameters to achieve the optimal cleaning result for each face. Interestingly, it appeared that some green corrosion products had migrated through the layers of wax; when this was gently removed with steam it became possible to see the underlying patina more clearly with the result that it became more uniform and saturated in colour. 

Following cleaning we were able to test new waxes and methods of application to improve protection of the sculpture in future. This showed that hot waxing with a clear wax in multiple layers had the effect of further enhancing the varied underlying colour of the patinated flat faces, bringing back some of contrasting browns and greens that must originally have been present. 

The pierced rings on the sculpture had lost much of the lacquer originally applied to preserve their polished appearance and had weathered over the years to a dark brown colour. Initial cleaning tests to determine the best method for polishing the rings revealed a heavy layer of an unexpected red corrosion product at the interface of the bronze. Although there was no time available for analysis at this stage in the treatment, the distinctive cherry red colour and slightly metallic sheen of this corrosion product suggested that it was copper(I) oxide (Cu2O). This is known to form on bronze through exposure to moist air and is usually the corrosion product immediately overlying the metal surface. Its appearance in such a thick layer on an outdoor bronze is atypical and may be related to the protected environment created by the lacquer. 

After removal of this red layer a more polished finish was finally achieved. Our discussions with the Hepworth Estate led the decision that we would aim to retain the texture that Hepworth added to the interior of the bronze rings with the idea that darker patina would remain in the recesses. The cleaned surface was then immediately lacquered using Incralac to prevent further colour change and darkening. We hope that this treatment has made it more possible to appreciate the combination of the artist’s intended colour contrasts with the polished rings whilst still respecting the sculpture’s natural ageing outdoors. Tate’s team will continue to monitor and maintain the sculpture annually to help preserve its condition.