1. The term ‘patina’ refers to the character of the material surface that develops with age. Patina interlayers in masonry are the thin surface layers resulting from weathering and treatment of the substrate over time. In general, patina in masonry is often regarded as a natural and positive characteristic, similar to the green corrosion layer that appears on copper and bronze and is valued for its colour and historical character.
2. ASTM E 1857, ‘Standard Guide for Selection of Cleaning Techniques for Masonry, Concrete, and Stucco Surfaces’. This guide outlines procedures for the selection and assessment of cleaning techniques for removing soiling and staining from masonry, concrete and stucco surfaces. The current version of the ASTM standard references British Standard BS6270 (1982), further discussed below.
3. The referenced standard is British Standard BS 8221–1:2000, ‘Code of practice for cleaning and surface repair of buildings, Part 1: Cleaning of natural stones, brick, terracotta and concrete’, issued by the British Standards Institution (BSI). Part 2 of this standard is subtitled, ‘Surface repair of natural stones, brick and terracotta’. This code of practice was prepared and adopted by Technical Committee B/209 of the British Standards Institution (BSI) and organizations such as English Heritage, Historic Scotland, Society for Protection of Ancient Buildings, the Royal Institute of British Architects, and other representative councils, associations, and research institutions throughout the UK. The current standard was updated from the previous British standard adopted in 1982.