GOLD & METAL LEAF CARE & MAINTENANCE
Gilding Care and Maintenance
Threats to gilding
Whilst gilding has been known to last for over 3000 years, the biggest threat it faces is from inappropriate cleaning and unnecessary intervention by those without adequate knowledge and training. The application of water during cleaning of water gilded surfaces causes considerable damage as the water dissolves the size that binds the gold leaf to the substrate. The use of cleaning solvents can have an equally disastrous effect. They dissolve the size used in oil gilding and remove the surface finishes (such as lacquer or varnish) resulting in the loss of colour and unprotected work. As gilding is fragile it should not be cleaned excessively. Only the occasional careful light dusting is necessary. Wherever possible excessive heat and light should be avoided. Care should also be taken with the positioning of lights and heating installations near gilded surfaces to avoid localised areas of damage being created. Heat and humidity can also lead to deterioration of the gesso layer and the substrate onto which the gilding is applied. This can result in cracking and loss of surfaces. Pests such as woodworm can cause damage in wooden substrates. In damp areas moulds can cause discoloration and loss.
Surface coating: After gilding has been applied it is sometimes coated for aesthetic reasons or protection. Silver gilding is always coated with varnish to prevent it becoming tarnished. The surface coating can take the form of lacquer, clear glaze, or toned varnish , depending upon the desired level of protection or required appearance. It should be maintained thereafter because removing it exposes the leaf and alters the appearance.
Care and Maintenance
Any maintenance or specialist conservation work on gilding should be kept to a minimum and, ideally, be carried out by a professional conservator. Before any work is undertaken it is important to properly identify as much as possible about the substrate, method of application and type of leaf. All surface finishes should also be fully understood before an appropriate approach to the work can be established. The aim should be to maintain the original surface as far as possible. This should include any glazing or varnish as these layers protect the leaf and are integral to the appearance of the finish. Where practical to do so, the same original materials and techniques should be used when maintaining or repairing gilded work. Where the deterioration of the prepared surface is the cause of damage, the application of size or similar glue based material can stabilise flaking gesso or bole. If the protective surface coating has been worn away to expose the leaf this should be replaced to prevent further wear
If missing patches of gilding need to be replaced this can be achieved without having to re-gild the whole surface. Replacement leaf can be applied and then toned down to blend in with the original finish. This approach is preferable and more economic than renewing the whole surface. Whilst gilding itself can last almost indefinitely, a major problem can arise through the deterioration of some substrate materials. This is particularly problematic with exterior gilding on iron railings as gilding can flake off along with rust. Where gilding has been applied to stonework there can also be problems when masonry decay occurs. Water ingress is one of the biggest culprits. Where this occurs and the loss of either external or internal architectural gilding is evident, action to halt the flow of moisture contributing to the deterioration of the substrate will be necessary before re-applying the gilding.
Perhaps the worst cause of unnecessary damage is the application of gold paint on top of gilding. As gold paint oxidises and discolours; a chemical process which cannot be reversed occurs. Widely used as an alternative to proper conservation, it can have disastrous results. The cost of removing the paint and replacing the gilded surface frequently proves prohibitive resulting in the loss of the original effect for ever. Where the original was gilded the subsequent application of gold paint should be avoided. Due to the cost and difficulties in carrying out appropriate repair to gilding, it is always advisable to seek advice from a suitably qualified professional with an appropriate knowledge of the techniques that were originally used.