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BIOPATINAS

The objective of the project is to propose an alternative biological treatment for the conservation-restoration of copper alloys artefacts. Taking advantage of unique properties of carefully selected fungal species, the project relies on the conversion of existing corrosion patinas into copper oxalates. In fact, thanks to their insolubility and stability even in acidic atmospheres, copper oxalates are expected to provide the treated objects with long-term protection and no aesthetical alteration.

During the EU-ARTECH project    (2004-2009), a strain of Beauveria bassiana isolated from vineyard soils highly contaminated with copper showed the best performance with almost 100% of conversion from copper hydroxysulphates and hydroxychlorides.

Photo
ESEM observations of a) culture of B. bassiana on a copper-enriched media with copper hydroxysulfates showing the embedded copper oxalates crystals. The same crystals are formed on corroded coupons with b) a copper hydroxysulfates patina and c) a copper hydrochlorides patina. Results achieved during the master thesis of A. Simon “Etude et optimisation de la formation fongique d’oxalate de cuivre sur du vert-de-gris en vue de la protection de monuments".

 

The efficiency of the innovative treatment developed on bronze monuments was further investigated within the BAHAMAS project    (2010-2012), Biological patinA for arcHaeological and Artistic Metal ArtefactS . In particular, the newly formed copper oxalates were in-depth characterized in order to define their properties (formation mechanisms, adhesion...), either on copper-enriched media or on corroded coupons. Cross-section examination suggested that the first micrometers of the urban natural patina are completely converted into copper oxalates, as showed in figure below.

Photo
ATR-FTIR raster scanning: a) visible light photomicrograph of a cross section of corroded coupon with an urban natural patina after treatment with B. bassiana, embedded in polyester resin: the box indicated the selected area for the ATR raster scanning. FTIR false colors representing b) the original patina composed of brochantite (region of interest 1105 - 1085 cm-1), c) the newly formed copper oxalates (peak area 1320 cm-1) and d) the embedding resin (region of interest 1735 - 1715 cm-1)

 

After initial successful attempts (FP6-EU-ARTECH, 2004-2009 and FP7-BAHAMAS, 2010-2012), the efficacy of the fungal treatment is now improved and validated against ageing procedures. The environmentally-friendly use of microorganisms for restoration of metal artworks that is now proof-tested, could present a breakthrough innovation for the conservation industry. The project should provide conservation professionals with access to a simple-to-use, reliable, versatile, environment-friendly and low-cost technology, for art objects, archaeological objects, architectural components, etc.

One of the expected outcomes is the development of an easy-to-use kit dedicated to conservators-restorers. A feasibility study without implementation partner that deals with the ageing of coupons replicating the commonly found patinas in nature has been approved by the Swiss Commission for Technology and Innovation (CTI) for an 18-months funding and is now ongoing.

In parallel, a complementary project has been made possible thanks to Gebert Rüf Stiftung, which is providing financing and monitoring progress. The treatment under development will be:

- proof-tested under ageing conditions through the exposure of real objects to aggressive weather conditions,

- proof-tested for the appearance, resistance to corrosion and cohesion of the biopatinas onto foundry object’s surface,

- standardized to become (and be perceived as) simple and efficient for all uses and consumers

 

Collaborations :

  • Laboratoire LAMUN
  • Haute Ecole Arc Conservation-Restauration , University of applied sciences Western Switzerland
  • CNR-ISMAR, Genoa, Italy

Contact

Edith Joseph, assistant professor

 

Monica Albini, PhD

 

Lidia Mathys-Paganuzzi, lab technician

 

Coralie Montavon, master student