May Cassar

Damage functions in heritage science

Abstract This contribution critically examines various concepts related to damage functions in current use; it does not represent a comprehensive review, however. In heritage science, damage functions can be defined as functions of unacceptable change, dependent on agents of change. Unlike in other domains of science, the reference to unacceptable change implies that a value-based decision needs to be applied to the analytically determinable change, or dose–response function. Since there are a number of values associated with heritage, there can be a number of damage functions describing one and the same physical or chemical process of change. For practical reasons, it is thus useful to decouple the value function from the dose–response function, as the latter can be independently deduced (empirically or experimentally). While the behaviour of single materials and objects is often modelled deterministically, the probabilistic approach can be used to describe the degradation of complex structures, e.g. buildings, although not commonly in heritage research. There is a case to be made for more in-depth exploration of incremental and stochastic processes of degradation of heritage materials and structures, and the associated values, with a view towards developing more damage functions. Damage functions find use in modelling for predictive maintenance. However, predictions are associated with uncertainty due to the need for extrapolation, and this is also rarely analytically examined. Validation of modelling processes is possible using accurate methodologies of asset monitoring, which would enable an effective appraisal of preservation strategies.

Looking beneath Dalí's paint: non-destructive canvas analysis

A new analytical method was developed to non-destructively determine pH and degree of polymerisation (DP) of cellulose in fibres in 19th–20th century painting canvases, and to identify the fibre type: cotton, linen, hemp, ramie or jute. The method is based on NIR spectroscopy and multivariate data analysis, while for calibration and validation a reference collection of 199 historical canvas samples was used. The reference collection was analysed destructively using microscopy and chemical analytical methods. Partial least squares regression was used to build quantitative methods to determine pH and DP, and linear discriminant analysis was used to determine the fibre type. To interpret the obtained chemical information, an expert assessment panel developed a categorisation system to discriminate between canvases that may not be fit to withstand excessive mechanical stress, e.g. transportation. The limiting DP for this category was found to be 600. With the new method and categorisation system, canvases of 12 Dali paintings from the Fundacio Gala-Salvador Dali (Figueres, Spain) were non-destructively analysed for pH, DP and fibre type, and their fitness determined, which informs conservation recommendations. The study demonstrates that collection-wide canvas condition surveys can be performed efficiently and non-destructively, which could significantly improve collection management.

A cross-disciplinary approach to the use of archives as evidence of past indoor environments in historic buildings

This article describes a methodology developed in consultation with English Heritage, The National Trust and Historic Royal Palaces. It links past environmental conditions in historic houses to object deterioration, using information from a range of disciplines. These include environmental history, building science, archival research and preventive conservation. The methodology was devised in order to integrate qualitative and quantitative evidence for a novel simulation of historic buildings. Application of the methodology has illustrated the value of integrating different strands of research to provide a robust synergistic approach to the complex problem of assessing natural ageing in historic materials. This approach will aid the understanding of both past internal climates and future object deterioration.

REPRESENTATION AND INTERVENTION: THE SYMBIOTIC RELATIONSHIP OF CONSERVATION AND VALUE

Abstract Physical and intellectual access to heritage is shaped by conservation through a long-term, cyclic and symbiotic relationship of representation and intervention (or lack of it). This informs future use and representation. Value (which may be assigned for different reasons) makes heritage. All heritage is valued for varied reasons. Some argue that heritage has inherent value; this is not covered in this paper. Some values are preferred over others in decisions on what to use or conserve. The process below describes a number of different recurring phases in this relationship, which differs with different kinds of heritage: 1. Various agents change heritage; 2. Change affects valued elements of heritage; 3. Valued elements affect how change is perceived; 4. What is perceived as damage affects decisions about conservation interventions; 5. Conservation affects which valued elements are most likely to be preserved; 6. Preserved elements influence how heritage is represented; 7. New forms of representation will affect future conservation decisions. Historically, how heritage has been represented has affected how an object is preserved. This affects later representation and use, making the relationship symbiotic.

OPTIMIZING DRYING STRATEGIES TO REDUCE DOWN TIMES FOR ACTIVELY-USED FLOOD DAMAGED HISTORIC BUILDINGS

Abstract The sustainability of historic buildings often depends on continued use. Institutions provide significant resources for repair and maintenance. Increased flood risk as a consequence of climate change is growing in a number of places. Once wet, a building could be unusable for a long time, leading to losses and possible abandonment. An initial study as part of the EU research project, Global Climate Change Impact on Built Heritage and Cultural Landscapes (Noahs Ark) has shown how novel computer modelling can predict how wood left to dry naturally will dry in future climates. This knowledge will help develop strategies for safe and rapid drying of flooded wooden buildings. Conventional rapid drying using mechanical dehumidification can cause large moisture gradients within wood, leading to mechanical stress and failure. It is hoped to find fast, safe drying regimes by optimizing the pattern of rapid and natural drying.