CERAMIC STANDARDS

Conservation Officers in most towns and cities wifi be confronted with buildings faced in terracotta. Some will be listed but most depend on being in conservation areas for any protection. Terracotta - comprising large blocks and slabs of moulded clayware - was used most widely on commercial and public architecture dating to the late- 19th and early 20th centuries. Such buildings have to earn their keep. Owners will expect any refurbishment to create a bright and commercially more attractive appearance. Costs will be vetted carefully against increased value or rentals. Only in exceptional cases can grant-aid be used to encourage the highest standards in any conservation project.

In this situation where conservationists have to work hard to convince owners, architects and builders of the need for sensitivity, the challenges presented by terracotta are compounded by the fact that there is still widespread ignorance about the nature of different types of architectural ceramic, and the merits and dangers of different approaches to cleaning.

This depressing scenario can be

Dr Michael Stratton

discusses the essential features of the material

taken further. Most of the key examples ofterracotta architecture in Britain have been irreparably damaged not by pollution or decay but by human intervention in the name of conservation. The fireskin and much of the decorative detailing on the Royal Albert Hall was blasted away by grit cleaning in 1972, and the surface of the nearby Natural History Museum was scored and bleached by hydrofluoric acid a few years later. This trail of abrasive destruction continues, with some commercial buildings now being cleaned every 3-5 years, as the rate of soiling increases due to loss of the smooth protective fireskin.

A new British Standard for the conservation of terracotta is awaited. Until it is ready, only broad principles can be put forward, along with a series of cautions about the damage which can inadvertently result from decisions over cleaning and partial replacement. This article urges a more conservative approach; offers some guidelines as to how Conservation Officers can try to understand ceramic architecture and the nature of terracotta; to then guide owners and architects through the maze of different technologies and options.

UNDERSTANDING TERRACOTTA

As a prelude to any recommendations or decisions, one needs to understand the nature of the material and the context in which it was used.’ Unglazed terracotta, typicallywith a natural colour of buff, grey or red, was made in the Tudorperiodbut then, farmorewidely, from the late 18th century. It can be readily distinguished from glazed faience, where the body is covered by one or more glazes. Confusion only arises with some of the vitreous finishes dating to the turn of the century, where a clear, matt glaze was applied to the fired body. Faience became widely used from the 1890s. The most usual colour for faience was a white or cream, bright polychromy inspired by Art Nouveau and Art Deco being reserved for more exotic projects. The unglazed surface of terracotta may be more vulnerable to soiling and is hence often the subject of more vicious cleanmg - buttheprotectivefireskin, achieved by smoothing over a block once it has been extracted from the mould and by giving it a full, high-temperature firing, is the key protective shield for the piece, as well as giving it its distinctive colour and texture.

To understand the nature of the surface, be it fireskin or glaze, it is necessary to appreciate the nature of the body, which, in turn, will depend on the clays used by the manufacturer. In most simplistic terms, firms either worked a single clay or created a mixture which (once mixed with water) would have a smooth texture and plasticity. Terracotta clays had to carry fine detail and then be fired to a high temperature without distortion or excessive shrinkage.

During the Tudor period, young surface clays from the south east of Eng
Building by numbers: hollow blocks of

terracotta being set onto brickwork for the Bournemouth Pavilion, c1930.

6

CONTEXT 52