Biopassivation Method for the Preservation of Copper and Bronze Artefacts

Edith Joseph

doi:10.3389/fmats.2020.613169

Abstract

A biopassivation method has been proposed as a new ecological and sustainable solution for preserving copper-based artefacts using selected microorganisms. This technology is based on the natural capacity of some fungi to form copper oxalates on the corroded surface of copper alloys. Existing unstable and pulverulent corrosion products are converted into an insoluble and chemically stable biopatina that provides the treated surfaces with a stabilization of the corrosion process and an aesthetically attractive green color. This treatment allows to stabilize the active corrosion induced for example by copper chlorides and to prevent green staining of surrounding materials (stone pedestal, wall…) due the leaching and loss of pulverulent and water-soluble corrosion products (i.e. copper sulfates). The behavior and performance of the proposed treatment have been followed during natural aging procedures, which have shown that this method stabilizes the corrosion process while having less chromatic variation compared to more traditional protective systems. The application protocol was then validated on real cases such as outdoor sculptures and archaeological objects. Based on these results, a ready-to-use kit is now proposed to conservators.

Highlights

In recent decades, biological methods have been increasingly proposed as ecological and sustainable alternatives for the heritage conservation, in particular for the cleaning of frescoes and ornamental stones (De Muynck et al, 2010; Troiano et al, 2013) there is a real interest in biotechnological applications, respectful of the environment and using no hazardous substances (Bharde et al, 2006)
For the past fifteen years or so, we have been exploiting the ability of a unique fungal strain to create copper oxalate patinas on archaeological and historical objects made of copper alloys
Just as the “patine du temps”, composed of calcium oxalates, forms on stone monuments, copper oxalates were observed on open air bronze monuments, while it is known that these compounds are not part

Summary

INTRODUCTION

Biological methods have been increasingly proposed as ecological and sustainable alternatives for the heritage conservation, in particular for the cleaning of frescoes and ornamental stones (De Muynck et al, 2010; Troiano et al, 2013) there is a real interest in biotechnological applications, respectful of the environment (at room pressure and temperature) and using no hazardous substances (Bharde et al, 2006) Designing such alternative methods, particular attention should be paid to durability, efficiency and toxicity. The biopassivation treatment is proposed as a ready-to-use kit composed of a gelified culture of Beauveria bassiana. To this purpose, the formulation is prepared with the following elements:. To wear gloves and face masks is recommended for this specific group of persons

Objectives

RESULTS AND DISCUSSION

DATA AVAILABILITY STATEMENT