Premise

An operation of conservational restoration generally follows a multi-disciplinary approach and is articulated in different phases that can be defined in temporal order: cleaning, consolidation, plastering and protection, preceded by a preliminary phase in which – following an accurate examination of the pieces- the methods and techniques to be employed are established.

This initial phase allows the direct observation of the piece in order to acquire the information on the state of conservation to identify which of the constituent materials present are original and which of these have contributed to degradation.

The operations begin with the detailed inventory and storage of the detached fragments, the pre-consolidation of the parts that are severely damaged and the application of bandaging to support or protect the fragments with partially detached pieces.

First the pieces undergo a removal of biological interference or micro-organisms, the removal of alien metallic elements and the preliminary treatment for oxides that may provoke corrosion when in contact with water in the subsequent phases.

Depending on the state of conservation of each individual piece, some operations such as the cleaning and plastering are always necessary while the consolidation and protection may be avoided in the case of pieces that are in an optimal state of conservation.

Cleaning

This phase is extremely delicate due to the risk of causing irreversible damage; therefore it is paramount that the operation is limited to the removal of what is damaging to the conservation of the stone material, respecting the overlying strata that may be able to reveal significant information about the history of the piece since its creation.

The treatments frequently employed are manual applications or compresses with absorbent materials, the use of resins for ionic or enzyme exchange and the use of instruments such as nebulizers, manual micro-tools, pneumatic or electric instruments, aero-abrasive devices, ultrasound and lasers.

Consolidation

This operation has the aim of recreating adhesion, cohesion and solidity to the stone structure, thus improving its mechanical resistance. The success of such operations is significantly linked to the possibility to penetrate the deteriorated stone with the consolidant, enabling it create a healthy nucleus that can form a united “body” .

The methods more commonly used are those which impregnate the stone using brushes, compresses and systems of capillary absorption. In the more severe cases and for works of limited dimensions, vacuum chambers are used or alternatively the piece can be immersed in chemical solutions that may allow the full penetration of adhesives.

In some cases it may be necessary to re-adhere fragments that are partially or totally detached; when such parts have a significant weight or size it may be necessary to insert fixed fittings as these can have the characteristics of inalterability in certain chemical conditions.

Plastering

This operation is carried out in order to provide the piece with a continuity to its surfaces, smoothing out lesions that may allow pollutant elements to penetrate the stone.

The materials used must be able to meet the requirements of the particular type of conservation and possess the requisites for an effective adhesion and the mechanical attributes similar to that of the stone. For this end, hydraulic or “aeree” plasters are utilized according to whether the work is being carried out on the surface or in depth, or plasters based on organic bindings.

The operation must not be limited to the correction of large lesions but must also include those more minute and it must also satisfy all of the aesthetic requirements including the precise coloration of the pastes used.

Final protection

The restoration concludes with the application of transparent chemical products and hydro repellents or covering layers or plaster, with the aim of creating a protective surface against the aggression of chemical and atmospheric pollutants.

The objectives of this final phase are not only of a conservational nature but also aesthetic in the cases of stains, strata or plaster that have a markedly accentuated colour, in order to arrive at an appropriate chromatic balance for the piece as a whole.

Finally it is important to remember the existence of “Normal Recommendations”, elaborated by an ad hoc commission governed by the CNR Centre for works of art of Milan and Rome and the Central Institute of restoration, to whom it is necessary to report throughout the duration of the restorational operation.