Biotechnology for objects conservation

John Scott

Abstract

As usual, discovery research and technology development for major industries is enabling new adaptations for conservation of cultural heritage materials. A scientific context is presented for consideration of biotechnology for applications in conservation. Qualitative aspects of methods already in use or under development are described and illustrated. Colleagues are encouraged to undertake new research and development.

Reduction, oxidation and chelation chemistries are fundamental not only to traditional aqueous cleaning and finishing, but also to newer biotechnological cleaning and finishing methods. Yet underlying processes are unfamiliar to most end users. I describe relevant science, and developing conservation biotechnology, reporting from a basic survey of relevant research, patent and marketing literature, and from a basic survey of conservation literature, and I describe and illustrate applied tests and test cases.

I briefly describe potentially useful microbes and their externally oriented metabolisms involving reduction, oxidation, or chelation mechanisms. Some microbes derive life process energy in oxidizing or reducing water-soluble ions including copper, iron, sulfates, etc. Some microbes alter their local ecologies by sequestering ions incompatible with their life. In care of heritage materials, such biochemical mechanisms may prove useful to remove metal or metal oxides from surfaces, to remove other mineral encrustations or stains, to redeposit mineral into eroded matrices, or for similar effects.

I then describe and illustrate current practical applications of these mechanisms, first the source technologies in mining and other industries. I describe, illustrate and critique a few potentially valuable applications already in use or under development for conservation of cultural heritage.

In copper, iron and gold mining, ores are pulverized and mixed with aqueous slurries of bacteria, i.e., sulfate-reducing bacteria. In the wet paste, bacteria reduce or partly reduce ore minerals, making metal easier to win. The paste is then wash-processed to separate reaction products for further refining. Post-process biochemical residues are considered ecologically much safer than traditional tailings rich in cyanide and other eco-poisons.

Sulfate–reducing bacteria and biosource chelators are also considered very effective in removing rusts from metal equipment and artifacts, with little or none of the collateral corrosion effects caused by traditional acidic derusting methods. For instance biochemical cleaning of life-critical diving hardware is permitted, although non-biochemical ammoniacal and mineral acid or alkaline cleaners are not permitted. Refining of patinas on metal items can proceed without using even the least aggressive traditional chemical or abrasive media, and sometimes without the need for hot or cold repatination. I also describe other biotechnology applications for cultural heritage in stone and other materials.

I address post treatment stability of treated objects, and issues of ill effects over the long term.

I include a basic bibliography (printed and online sources) to guide readers into the literature and technology.