Stone Conservation: An Overview of Current Research (2010)

Stone Decay 3ize terminology (Stone Federation of Great Britain 1991), governmentalorganizations (Grimmer 1984), and research groups (Fitzner, Heinrichs,and Kownatzki 1997).The ICOMOS-ISCS Illustrated Glossary on Stone DeteriorationPatterns (Vergès-Belmin 2008) helps define and clarify usage across languagesand within the stone community, providing useful definitions ofterms such as scaling, spalling, and flaking. Weathering is generallydefined as the result of natural atmospheric phenomena, while decay is“any chemical or physical modification of the intrinsic stone propertiesleading to a loss of value or to the impairment of use,” degradation is“decline in condition, quality, or functional capacity,” and deteriorationis the “process of making or becoming worse or lower in quality, value,character, etc.” Some interesting details of the history of stone glossariescan be found in the introduction to the glossary.A more guided approach than a glossary can be found in work onexpert systems from the late 1990s, with Van Balen (1996; 1999) producingan atlas of damage to historic brick structures as part of an expertsystem for elucidating environmental effects on brick. The atlas evolvedinto a broader program known as the MDDS (Masonry DamageDiagnostic System) (Van Hees, Naldini, and Sanders 2006; Van Hees,Naldini, and Lubelli 2009). Expert systems have gone in and out of fashionover the past fifteen years, but the need to capture expert experienceand judgment has become ever more urgent, given the large number ofconservation professionals nearing retirement age.Fitzner has produced an important classification of weatheringforms as a basis for mapping the deterioration across a building facade(Fitzner, Heinrichs, and Kownatzki 1997). This system has also been presentedin case studies (Fitzner, Heinrichs, and La Bouchardiere 2004).Such complex systems have been criticized because of the number ofparameters to be measured (Moraes Rodigues and Emery 2008) as wellas “cost concerns and the extensive training they require” (Dorn et al.2008). Fitzner’s classification recognizes nineteen different weatheringforms and goes some way toward recording the severity of each, basedon visual inspection (Fitzner 2004). Similar, but simpler systems havebeen described by Massa, Naldini, and Rorro (1991) and by Vergès-Belmin (1992). Zezza (1990; 1994; 2002) has used digital image processingto map different forms of surface decay. Starting with photographsand other nondestructive information, such as ultrasonic measurements,false color images are produced that identify particular forms of decay.HOW SERIOUS IS IT?MEASURING THE EXTENT AND SEVERITY OF DECAYIn order to make real progress, we need to quantify decay. In otherwords, in addition to describing the type of decay, it is essential that weare able to measure its extent, or the area it covers; its severity, or howadvanced the decay is; and the rate of decay over time. First, we need todo so in order to unravel its various causes. For example, how can we say