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Green Solvents What are Green Solvents and why are they important in conservation?

Author: Mariana Escamilla



In a survey recently made by SiC, results confirm solvents are one of the most used materials in conservation; it also confirmed the interest of conservators for knowing more about toxicity and alternative materials. The survey was answered by approximately 150 conservators of different specializations and countries.



SiC survey results. Image credit: SiC.

It is known that solvents are detrimental to the environment, health and possibly, also for the objects. In the specific case of the conservation and restoration of paintings, the use of solvents for surface cleaning of varnish removal will undoubtedly have a leaching effect, and therefore possibly have an impact on the flexibility and later deterioration of the paint (For more Information: FELLER, STOLOW, JONES 1985; SUTHERLAND, PHENIX 2011; FIFE et al. 2015). Nonetheless, conservators keep using them, sometimes even the most toxic ones, for the sake of accomplishing the goal of a conservation/restoration concept.


Conservators are familiarized quite early in their professional development with phrases such as – “solvents are to be used carefully”, “solvents might be toxic” and “...they can be dangerous for fetuses”, moreover they “might be carcinogenic”. We learn how to use them responsibly in a working situation, and we can protect ourselves from the direct contact with the solvents while working with them. However, what happens to them after they evaporate and get lost in the atmosphere?


This might be a logical thought, but personally, I haven’t thought about what happens with solvent vapours afterwards.


The answer surprised me – evaporated solvents might bind with the water in the atmosphere and reach the soil again. A lot will be degraded by micro-organisms in the soil or photo-oxidise in the atmosphere (More about this topic). Nonetheless, the problem is not its biodegradability – the problem, as always, is the quantities of solvent vapours released into the atmosphere. An example for this is the amount of fumes released into the atmosphere during the production of Acetone, in which 97% of it is lost. So, the product we have used so often for cleaning is what results of the 3%.


During my BA Degree, I wrote a paper about paint strippers, their use in conservation and the way they work (if interested in Commercial Paint Strippers, check the interesting paper by WOLLBRINCK 1993). While reading the various literature, I noticed “Green Solvents” were mentioned quite often.


Are there green alternatives to solvents? And if so, why are we as conservators not using them?


The only explanation I could think of was: there is not enough research, or at least not yet published, to support their use.


So, first of all, what is a “Green Solvent”?


While looking for a definition, it was useful to focus on the Green Chemistry definition and principles.


Paul Anastas is well known for his work in defining and spreading the concept of Green Chemistry – the following image lists 12 principles that should be taken into consideration (here a link where the 12 principles are explained, you will be able to click on each one of them and read a more detailed description:


Image credit: www.acs.org.

In the fifth point: “Benign Solvents & Auxiliaries”, the issues around solvents are described.

Solvents are problematic because of, for example:

  • Toxicity: “Solvents are also the major contributors to the overall toxicity profile and because of that, compose the majority of the materials of concern associated with a process. On average, they contribute the greatest concern for process safety issues because they are flammable and volatile, or under the right conditions, explosive.”

  • Major Energy Consumption during Production: “Solvents and mass separation agents also drive most of the energy consumption in a process. Think about it for a moment. Solvents are alternately heated, distilled, cooled, pumped, mixed, distilled under vacuum, filtered, etc. And that's before they may or may not be recycled. If they're not recycled, they are often incinerated.”


The term “Green Solvent” is a new classification but some of the solvents belonging to it are not new – in fact, the greenest solvent of all has been widely used through history: water. Therefore, one can deduce that "Green Solvents” are non-toxic, environmentally friendly during production, use, and disposal. Bio-derived chemicals, for example, “are frequently environmentally benign, and they have short regeneration cycles which meet the demands of a sustainable chemical industry”. (WYPYCH 2014, p. 2)


Nonetheless, the reality is not ideal. A “Green Solvent” must only have one of the characteristics mentioned above to be considered “green”.


To design a solvent that can replace certain others is not easy at all: “Minimizing toxicity, while simultaneously maintaining function and efficacy, may be one of the most challenging aspects of designing safer products and processes.” (Source: N.D. Anastas. Designing Safer Chemicals).


Often, the optimization of a solvent is only possible to one green concept, for example, it might not be as toxic, but its production will consume as much energy as the production of other non-green solvents.



DO WE NEED GREEN SOLVENTS?

Green Chemistry exists, and so do “Greener” alternatives to solvents that we are using right now. More research is needed to be able to recommend and use these solvents fully and make sure they are not detrimental to the object (or at least harmful to a similar level to the ones we are usually using).


Conservation needs to look further to more environmentally friendly practices. The use of solvents, in general, should be diminished. Furthermore, if necessary – and after further research results are published – green alternatives, perhaps even the omission of solvents, should always be considered first (of course, depending on the characteristics of treatment and state of the object being treated).


We need to look into the green chemistry and be innovative.


Fellow conservators, go green!



Sources:

FELLER, STOLOW, JONES 1985

Robert L. Feller ; Nathan Stolow ; Elizabeth H. Jones. On picture varnishes and their solvents. Ohio 1985.

FIFE et al 2015

Gwendoline R. Fife Bascha Stabik Allison E. Kelley Jared N. King Bernhard Blümich René Hoppenbrouwers Tyler Meldrum. Characterization of aging and solvent treatments of painted surfaces using single‐sided NMR. In: Magn. Reson. Chem. 53 (58)

SUTHERLAND, PHENIX 2001

Ken Sutherland and Alan Phenix. The Cleaning of Paintings: effects of organic solvents on oil paint films. In: Studies in Conservation Vol 46. 2001 Washington. p. 47-60.

WOLLBRINCK 1993

Wollbrinck, Thomas. The composition of proprietary paint strippers. In: Journal of the American Institute for Conservation 32, no. 1 (1993), pp. 43-57 American Institute for Conservation of Historic and Artistic Works, Washington, DC, United States.

WYPYCH 2014

Anna and George Wypych. Databook of Green Solvents. 2014 Toronto.

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Sustainability in Conservation is an online network providing resources and information about environmentally responsible practices  in art conservation and related fields. Within a practice that produces so much waste, we hope to inspire collaboration and awareness to make cultural heritage a more sustainable profession. 

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