BCD 2018

INTERIORS 5 163 C AT H E D R A L COMMU N C I AT I O N S C E L E B R AT I N G T W E N T Y F I V E Y E A R S O F T H E B U I L D I N G CO N S E R VAT I O N D I R E C TO R Y 1 9 9 3 – 2 0 1 8 extremely effective ways of preserving the paintings in good condition. In particular, the importance of maintaining water disposal systems cannot be overstated. Remote monitoring of inaccessible water disposal services such as valley gutters or high level hoppers are increasingly available and affordable. Managing exposure to direct sunlight may be partially addressed by the installation of UV filters, but careful investigations are frequently required to understand the actual impact of light on the painted surface. Passive conservation often involves the introduction of environmental control systems. Such solutions are designed to minimise deterioration resulting from the impact of the unstable microclimate and water in vapour form, which is the main activation mechanism for soluble salts and micro- organisms. Further passive interventions may include the removal of impervious paints and renders, the removal of thick vegetation and the improvement of drainage systems. All such interventions require careful monitoring to determine their impact on wall paintings. Installation of control monitoring may be necessary in order to re-evaluate the results and identify potential errors. Remedial treatment The approach to remedial treatment should follow the ‘less is more’ principle, prioritising conservation procedures aimed at improving the stability and strength of the original painting. From the conservator’s point of view, restoration is rarely considered to be a necessary stage of the project, but it is often desired by the client. There is no standard recipe for remedial treatment of wall paintings, but there are some general rules which need to be observed: • the materials and methods should not introduce change to the character and appearance of the original painting • the materials have to be stable and compatible with the original, and they must not have a detrimental effect on the historic fabric or impede future conservation treatments • the painting should never be treated in isolation from its substrate and the overall structure, and causes of detrimental change must always be addressed first • wherever possible, treatments should be reversible. Methods of remedial treatment vary depending on the requirements but may include: • emergency works aimed at preserving cohesion and protecting the wall painting before or during other interventions • stabilisation of the substrate • filling and repairs • consolidation of paint layers • surface cleaning and removal of other surface accretions, including overpaints and conservation materials • retouching (‘colour re-integration’). Emergency works typically involve facing the surface with tissue of varying properties and grades, depending on the purpose of the facing. These are applied using adhesives which are reversible in solvents that will not damage the painted decoration. Emergency pre- consolidation may be undertaken when flaking and powdering of paint layers occurs to an extent where other treatments could result in damage. This is frequently a preferred option where direct application of a facing tissue would be likely to result in random relocation of severely distorted and detached paint flakes. The transfer of wall paintings onto replacement supports was sometimes undertaken in the 20th century but this is no longer a recommended practice. It may be used in critical situations such as where the underlying structure cannot be saved and it is the only way to rescue the decoration. Substrate stabilisation is required if unstable hollow areas exist between the layers of plaster and/or substrate, but filling blisters where there is no risk of fabric loss should be avoided. An injectable grout should be selected which is compatible with the original mortar (matched to its current condition rather than the original recipe), but it also has to have particular working properties which allow its smooth application by injection and which allow it to cure in the specific environment, frequently in the absence of air. In terms of performance, the grout must also provide a stable bond with the substrate within a reasonable time and with minimal shrinkage. Mineral grouts based on hydrated lime (usually lime putty or dispersed lime) or hydraulic lime are considered the most suitable materials, mainly for their compatibility with lime mortars, but also for their adjustability and performance characteristics. A quicker set can be achieved by using dispersed lime, mature lime putty, or nanolime. The latter, being dispersed in alcohol, also reduces the moisture transferred to the wall. Methods of partial substitution of water with alcohol are also being extensively tested. Other procedures which include resin consolidants may be justified, but resins are unlikely to be chemically or physically compatible with the wall painting. The materials used for substrate repairs should always be compatible with the original and should never be stronger than the surrounding fabric. Repairs to the plaster substrate may be required to target any ongoing or potential instability. These usually consist of filling cracks and re-plastering localised areas using appropriate lime mortars, often after removal of old inappropriate and unsightly cementitious or gypsum repairs. Stable hairline fractures are normally left undisturbed because they can help to buffer tensions within the substrate, and filling can result in widespread failure. Successful consolidation of powdering or flaking paint layers usually requires repeated treatment at various stages of the remedial process. Although ideally it should not precede surface cleaning, it is commonly needed much earlier to minimise damage to paint layers during stabilisation of plaster or other works, such as those involving structural interventions. A variety of materials and methods may be used as consolidants, depending on the character and condition of Removal of discoloured varnish may significantly improve the legibility of paintings, Stanford Hall, Leicestershire Temporary securing of large paint flakes during consolidation may be introduced to avoid further loss, Gorton Monastery, Manchester