Distribución pasada y futura del color en edificios históricos de piedra

Abstract

RESUMENLa distribución del color en edificios de piedra varía con el tiempo. En el pasado, el ennegrecimiento se debía principalmente a la combustión de carbón. Actualmente, se debe fundamentalmente al depósito de partículas derivadas del diesel. En el futuro, se verá modificado por la acción de la lluvia y el viento. La percepción del público sobre el ennegrecimiento depende de su distribución. Si se resaltan las formas arquitectónicas, será en general aceptable. Los umbrales de aceptación también dependen de la concentración de carbono elemental. Si la concentración es elevada, como en áreas de tráfico intenso, los edificios estarán oscurecidos y probablemente se percibirán como inaceptablemente sucios. A menores concentraciones de carbono elemental (2-3 µg m -3 ), el aspecto de los edificios es en general más aceptable. En el futuro, los cambios de color se verán favorecidos por la diferente actividad biológica, resultante del cambio climático y los diferentes tipos de contaminantes. Un proceso de amarilleamento será probablemente más relevante. Las partículas derivadas del diesel son ricas en compuestos orgánicos que se pueden oxidar a materiales similares a sustancias húmicas (HULIS) de tonos marrones.Palabras clave: pátina, distribución del ennegrecimiento, contaminación atmosférica, cambio climático, estética. SUMMARYThe patterns of colour on stone buildings change with time. Buildings were blackened by coal soot, but now mostly diesel particles and in future, wind-driven rain may alter the patterns and oxidation of surface organics. Colouring patterns that outline or shadow architectural elements are publicly more acceptable than those that cut across them e.g. rain streaking. Thresholds of acceptability for blackening can be related to soot loading. When soot loading of the ambient air is high, e.g. near busy roads, buildings are dark and typically viewed as unacceptable. However at lower concentrations (2-3 µg m --3 elemental carbon), building appearance is typically seen as more acceptable. The future offers a potential for variation in building colour, arising through different biological growth under changing climates or the presence of different pollutants. In future urban atmospheres more dominated by organic pollutants a yellowing process may be more important. Diesel soot has many organic compounds that can oxidise to brownish-coloured humic-like (HULIS) materials.

Tuning and Effectiveness in Heritage Models

“…Declining levels of air pollution in recent years have been beneficial to heritage [36], while concern over climate change impacts has increased e.g., the Noah's Ark Project [6]. Past exposure conditions for sites and objects can be difficult to determine, and although some have tried, e.g., assessment of historical weathering [37], examining the deposits on buildings [38][39][40], archive photographs [41,42] and economic records of repair [43], it can be difficult. Thus, there has been considerable interest in trying to model conditions in the past and relate them to observed damage [34,44,45].…”

Effect of Artificial Freeze/Thaw and Thermal Shock Ageing, Combined or Not with Salt Crystallisation on the Colour of Zamora Building Stones (Spain)

“…One of the aesthetic parameters of a building stone is its colour, which contributes greatly to its ornamental value. As with other properties, colour monitoring is of great importance to evaluate treatment effectiveness when the stone is subjected to conservation or restoration treatment [10][11][12][13][14][15][16], to assess changes by accelerated ageing tests [16][17][18][19][20][21][22] and to in situ deterioration in the building [3,[23][24][25][26][27][28][29]. In most of the works cited, stone building materials, after the application of conservation treatments (waterproofing, consolidation, desalination, etc.…”

Monitoring façade soiling as a maintenance strategy for the sensitive built heritage

“…In highly polluted urban areas, the concentration of particulate matter is the primary cause of the façade soiling that induces heritage building decay (Bonazza et al, 2007;Grossi and Brimblecombe, 2008;Rampazzi et al, 2011;Barca et al, 2014). The adverse visual impact resulting from colour patterns on these façades may be detrimental to a building's architectural value.…”

“…Pale-hued construction materials are particularly vulnerable to progressive soiling and the concomitant aesthetic decay (Grossi and Brimblecombe, 2008;Grossi et al, 2003). One of the many factors that condition façade soiling is architectural design-dependent deposition and retention of particulate matter on material surfaces (Pio et al, 1998).…”

“…The perception of façade soiling has been evaluated with non-destructive techniques: applying greyscale in photographic images to decipher the rates of re-soiling associated with cleaning/soiling cycles (Searle et al, 2000), monitoring the progressive decline in lightness (L*) values over time (Grossi et al, 2003), quantifying soiling with integrated digital photography and image processing (Thornbush and Viles, 2004;Thornbush, 2010;Janvier-Badosa et al, 2013), or assigning lightness (L*) perception based on a soiling index (Thornbush, 2014). Visual impact resulting from façade aesthetic decay entails establishing aesthetic tolerance thresholds in terms of human sensibility to colour patterns (Grossi and Brimblecombe, 2008;Grossi et al, 2003;Grossi and Brimblecombe, 2004), estimating when (Marie, 2013) or exactly where on façades cleaning operations are needed (Swann, 2013).…”