Revisiting and reanalysing the concept of bioreceptivity 25 years on.

2020 marks 25 years since Olivier Guillitte defined the term 'bioreceptivity', to describe the ability of a building material to be colonised by living organisms. Although Guillitte noted in his 1995 paper that several issues required further investigation, to the best of our knowledge the bioreceptivity concept has not been restated, reviewed, reanalysed or updated since then. The present paper provides an opinionated exposition of the status and utility of the bioreceptivity concept for built heritage science and conservation in the light of current knowledge, aimed to stimulate further discussion. A bibliometric analysis highlights the key dimensions of the past 25 years of published research, showing that the term bioreceptivity has been widely used in the field of built cultural heritage. In our reanalysis of the concept, special attention is devoted to the six types of bioreceptivity (primary, secondary, tertiary, intrinsic, extrinsic and semi-extrinsic) articulated by Guillitte in 1995. We propose that field-based studies of bioreceptivity are urgently needed, and that the intrinsic, extrinsic and semi-extrinsic types of bioreceptivity should be dropped, and a new category (quaternary bioreceptivity) added. Additionally, we propose that bioreceptivity in submerged and subsoil environments should also be considered. Bioreceptivity remains an important concept for managing both new build and built heritage, as it provides the key to understanding the drivers and patterns of biological colonisation of building materials.

Soiling and decay of N.M.E.P. limestone tablets.

The British National Materials Exposure Programme (N.M.E.P.) ran from 1987 to 1995 and involved exposure of a range of materials samples (including tablets of Monks Park and Portland Limestones) at over 20 sites around Britain for 1-, 2-, 4- and 8-year periods, under known climate and pollution conditions. Deterioration of the limestone tablets has previously been recorded in terms of weight change, contents of soluble salts, and visual soiling. In the present study samples from exposed and sheltered positions at Wells, Bolsover and Lough Navar have been studied using a spectrophotometer, optical microscopy and scanning electron microscopy (SEM) to investigate the distribution and nature of particulate material and its role in soiling and decay. Clearly, recognisable pollutant particles such as perforated cenospheres, are only rarely present. Organisms and organic remains, including filamentous microorganisms and pollen grains, are widely distributed. At each site, soiling has different characteristics in terms of composition and change over time related in part to differences in climate and pollution histories. There is no general link between degree of soiling and amount of decay (in terms of surface recession) as the nature of decay is a key influence on the relation between soiling and decay.