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Calcium hydroxide nanoparticles for the consolidation of

wall paintings

P. Baglioni, D. Chelazzi, L. Dei, R. Giorgi

AimsConsolidation of wall paintings with compatible inorganic materials.ResultsCriteria for conservation treatments, such as compatibility, minimal intervention or

reversibility, have found only in the last years some practical applications with the emerging of

new techniques based on nanotechnologies. Nanotechnology is based on the recognition that

particles of size below 100 nm impart to nanostructures formed from them new behaviour and

properties.

After the 1966 Florence flood, the research group directed by the CSGI co-founder Prof. Enzo

Ferroni was one of the first Academic Institutions that applied a rigorous scientific approach to

the investigation of Cultural Heritage conservation. In 1969, at the International ICOM

Conference in Amsterdam, a new method for in situ wall paintings consolidation was proposed

by Enzo Ferroni. The method, today known as barium or Ferroni-Dini method, inverts the

chemical reactions that produce the degradation of wall paintings, stabilizing the structure of

the mortar and regenerating the binder of the painted layer, that is calcium carbonate. The

method is based on the application of cellulose compress soaked with ammonium carbonate

and barium hydroxide solutions. The consolidation is achieved two different chemical

processes: the formation of fresh portlandite or calcium hydroxide, Ca(OH)2, through the

action of barium hydroxide on calcium carbonate, and the slow and gradual formation of

barium carbonate, BaCO3. The new slaked lime (Ca(OH)2), formed in situ, acts as the fresh

binder, giving new setting for mortar.

Consolidation of mural painted surfaces (or stones) by inorganic treatments should provide the

right content of carbonate binders to confer long-term preservation to the works of art. Ferroni-

Dini method was the first that provided reliable results and its success was mainly related to

the possibility of removing salts that threaten the paintings, reinforcing at the same time the

porous structure. The evolution of Ferroni-Dini is based on calcium hydroxide that is the best

binder for limestone and wall paintings. In fact, the whole physico-chemical compatibility

between the original and the restoration materials can be completely achieved by usingcalcium hydroxide that is the 'original' binder used by artists. We were among the first able to

synthesize Ca(OH)2 nanoparticles. Kinetically stable dispersions can be obtained in short-

chain aliphatic alcohols. The dispersions of nanoparticles are similar to an extremely

concentrated solution of lime water (up to 30% volume fraction), well above the physico-

chemical limit imposed by the solubility of calcium hydroxide in water.

At the moment calcium hydroxide nanoparticles application for wall painting consolidation

can be considered as a revolutionary alternative to the use of synthetic polymers (i.e. acrylic).

This method is currently used in several places in Italy and in other countries; in particular,

among others, for the conservation of mesoamerican paintings in Calakmul, Tlatelolco, and

Cholula in Mexico, and the consolidation of wall paintings in Sweden and Denmark. CSGIcontribution mainly consists in a scientific co-operation with conservators and institutions for

experimentation and application of this innovative methodology.

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CTS company (Italy) is now distributing in several countries the product with tradename

Nanorestore that is produced at the CSGI laboratory. Nanorestore is the first chemical

product based on nanotechnology, made available specifically to the conservator community.

La Antigua Ciudad Maya de Calakmul, Mexico: pyramid and wall paintings recently

discovered therein and preserved by using Ca(OH)2 nanoparticle dispersions

References

Baglioni P., Giorgi R., Dei L., Soft condensed matter for the conservation of cultural heritage,

Compte Rendus Chimie, 2008, XX, 1-9, article in press.

Dei L., Bandini F., Felici A., Lanfranchi M., Lanterna G., Macherelli A., Salvadori B., Pre-

consolidation of pictorial layers in frescoes; the high performance of CSGIs method based onnanolime evaluated by OPD team in Agnolo Gaddis La Leggenda della Vera Croce, Santa

Croce, Firenze, In Proceedings of the 23rd International Congress Il consolidamento degli

apparati architettonici e decorativi. Conoscenze, Orientamenti, Esperienze, Arcadia Ricerche,

Venezia, 2007, pp. 217-224.

Baglioni P., Giorgi R., Le nanoparticelle per la conservazione ed il restauro del patrimonio

culturale, Giornate Lincee della Chimica, VII edizione Contributi della chimica alla

soluzione di alcuni problemi della societa moderna, Accademia Nazionale dei Lincei, Roma

2007, Bardi Editore-Editore Commerciale, 81-97.

Baglioni, P., Giorgi, R., Soft and Hard nanomaterials for restoration and conservation of

cultural heritage, Soft Matter, 2, 2006, 293-303.

Giorgi, R., Chelazzi, D., Carrasco, R., Colon, M., Desprat, A., Baglioni, P., The Maya site of

Calakmul: in situ preservation of wall paintings and limestone by using nanotechnologies,

The Object in Context: Crossing Conservation Boundaries, Munich IIC Congress 2006:

proceedings, Edited by David Saunders, Joyce H. Townsend and Sally Woodcock, 2006, 162-

169.