Scottish market crosses: the development of a risk assessment model.
Thomson, Lindsey Jane
MetadataShow full item record
The purpose of the research was to investigate the causes and effects of stone decay and soiling upon Scottish market crosses, and to develop a risk assessment model for this monument type. Risk assessment methods are otherwise used in spheres of business and industry. This research is unique in exploring the possibility of applying these techniques to the study and prediction of monument degradation. Additionally, the research is the first synthesised study of market crosses since 1928. A mapping methodology was developed in order to record the condition of a sample of Scottish market crosses. Visible evidence of the erosion, soiling and conservation of these monuments was collected and analysed in relation to various associated weathering factors. A risk assessment model was then developed for predicting the future condition of such monuments. Integrated with this, intervention criteria and conservation guidelines were also produced aimed at those charged with the care of market crosses. The model was applied to a case study to assess the risk of degradation of the tested monument. The method was found to work in practice, and could be used by practitioners in the future. The methodology for the research can be summarised as follows. Based upon the literature review, hypotheses were formulated regarding the effect of various weathering factors upon decay and soiling patterns. Data for all surviving market crosses in Scotland was co11ected from archives and publications. A pro-forma and relational database were designed to hold an of the gathered data. A sample of 27 crosses was selected for detailed analysis. An increased level of data was col1ected for the sampled crosses, and a programme of intensive fieldwork was undertaken at these. Evidence for a11 visible decay, soiling and conservation treatment was mapped onto a detailed elevation sketch of each facade of every sampled cross. The decay and soiling were also classified according to intensity level and surface extent, based upon evidence from visual observation. In addition to the drafted mappings, the visited monuments were subject to a photographic survey. The collected data were analysed by interrogating the database and by applying a variety of statistical tests. A number of significant relationships were indicated between the various decay/soiling types and weathering agents. It was found that the patterns of decay, and particularly soiling, were greatly influenced by the monument characteristics, primarily due to the degree to which the stone was exposed to moisture ingress. Environmental factors were also found to have some influence, particularly the nature of the ground surface and the land-use type. Surprising1y, the leve1 of nearby traffic was found to have little effect. Climatic factors were shown to be significant in relation to a few decay/soiling types. However, the contradictory nature of these trends suggested that the ranges within Scotland may be too limited to have much real effect upon the observed variations in decay/soiling. Previous intervention was found to have some significant effects, particularly in the case of chemical stone cleaning. Risk levels for each significant relationship were calculated from the rate of occurrence and the amount of stone degradation observed in the sample. The sample risk model was developed to produce a pro-forma designed for use by practitioners involved in managing Scottish market crosses. Practitioners could use the designed system to regularly record the condition of other crosses and assess the extent to which they are at risk from decay/soiling due to various weathering agents existing at each site. Intervention criteria were also produced in order to advise the practitioner on when and how to intervene to stall the current decay or to reduce the risks of future degradation of crosses in their care. Methods were also suggested for interpreting and promoting market crosses to the public.