INTERVENTI DI CONSERVAZIONE DEI BRONZI IN AMBIENTE URBANO - TECNICHE INNOVATIVE DI INIBIZIONE DELLA CORROSIONE

Mauro Matteini

Istituto per la Conservazione e la Valorizzazione dei Beni Culturali del CNR, Sesto Fiorentino (FI), mmatteini@inwind.it

ABSTRACT

The restoration of bronze monuments located outdoors in urban area is articulated into a sequence of operations, each one with specific conservation aims. Cleaning, usually the first operation that is carried out, is finalized to remove from the surface foreign materials such as degraded products of past restorations, unstable products (especially incoherent patinas), harmful products (soluble salts, unstable substances) or any material that determines a falsifying aspect. Cleaning may be followed by a treatment for inhibiting corrosion; finally the intervention ends with the application of some hydrophobic coating. Sometimes, intervention for re-harmonizing the surface color is also performed.

The present paper focuses mainly on the issue of corrosion inhibition, starting from the methods available so far. It illustrates an innovative treatment that has been now also tested on a series of monuments in Milan (listed in the text). The method, now known as 'The Sodium Oxalate and Lime water method', has come into use only recently (2011), during the restoration of an important equestrian monument in Lisbon (the bronze statue of Dom José in Praça do Comércio). It is a treatment aimed at blocking the well known process of 'bronze cancer', by acting directly on the dangerous cuprous chloride (Nantokite). In the paper the author refers on the principles on which the method is based and illustrates the application protocols.

Parole chiave/Key-words:

conservation-restoration, bronze-monuments, corrosion-inhibitors, sodium-oxalate, lime-water