18 Y E A R B O O K 2 0 1 4 For example, the stained glass at Canterbury Cathedral is being eroded by acid rain. The sulphuric acid and sulphur dioxide in rainwater react with the alkali and calcium in the glass, forming sulphates, which are chalky and opaque. As this chalky crust is washed away, a new surface is exposed and pits start to appear in the stained glass panels. The pitting then allows acid rain to attack the inner surface of the glass causing even more damage. Moreover, as the weathered crust is hygroscopic in nature, it absorbs water and accelerates the deterioration process. Without analysing and understanding the science of the problem one cannot attempt to stop the deterioration and restore the artefact. One solution is to secondary glaze the stained glass to keep the rain off the historic surface. A pane of glass that is not attached or glued to the stained glass can be used as an external lining to protect the exterior of the stained glass from pollutants. Humidity and temperature between the two panels, however, must be controlled. The inner surface of the glass can be protected by the provision of a controlled climate combined with an air-filtration system to avoid condensation. But the design and installation of this secondary glazing requires great skill and creativity to prevent the protective glazing framework being obtrusive and affecting the beauty of the stained glass. The conservation of stained glass therefore draws on knowledge and skills from both the arts and the sciences. The same can be said more generally of repairs and other conservative interventions, as demonstrated in Anna Keay’s article (see page 21). The remarkable renewal of Astley Castle was made possible by a detailed understanding of building fabric (both old and new) and by a subtle appreciation of aesthetics. Similarly, Robin Kent’s advice on conservative repair (see page 29) extols both the importance of a scientific understanding of how repair materials will interact with historic components and such aesthetic concerns as allowing conservation repairs to weather-in naturally. Conservation, of course, isn’t just about working directly with historic fabric. As Jo Evans’ article (see page 37) demonstrates, heritage protection often relies on the skills of negotiation, persuasion and lobbying – skills that seem to belong more naturally under the banner of arts than sciences. That said, her article also shows that for ‘artful’ negotiations like those between conservation officers and homeowners to be successful, a scientific application of reason, objectivity and clear, accurate communication is often necessary. The traditional association of the arts with free-thinking creativity and of the sciences with the rigorous application of processes is, in any event, an over-simplification – all disciplines need the application of both creativity and rigorous process. The best science requires creative thinking: someone has to see a problem, form a hypothesis about a solution, and then figure out how to test that hypothesis. For artists, creativity alone will fail to deliver anything of worth. A musician or painter must also learn technique (or method), sometimes as rigorous and precise as found in any science, in order to turn their creativity into art. When designing the external lighting of a building or monument the lighting specialist has to understand the technology and equipment available. As Paul Millar’s article (see page 32) explains, the choice of light source and its effects need to be understood in order to design a lighting scheme that enhances and highlights the architectural detail and composition of buildings. Artistic interest is a relatively new addition to heritage protection and legislation. The Planning (Listed Buildings and Conservation Areas) Act 1990 refers to architectural or historic interest in respect of listed buildings and conservation areas. In 2012 the National Planning Policy Framework (NPPF), defining the term significance, stated that the value of a heritage asset is due to its ‘heritage interest, and that interest may be archaeological, artistic or historic’. The antecedents for this go back (at least) to the 1979 Burra Charter, which defined cultural significance ‘as the aesthetic, historic, scientific, social or spiritual value for past, present or future generations. Cultural significance is embodied in the place itself, its fabric, setting, use, associations, meanings, records, Minimum intervention: a mason from Historic Property Restoration Limited carries out lime mortar repointing work at Brizlee Tower, Northumberland (1781, Grade I). Conservative repair is discussed in Robin Kent’s article on page 29 (Photo: Robin Kent)
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