Preserving the Past for the Sake of the Present: The Science Behind Art Conservation
The Aims and Importance of Art Conservation
Art is not just another "pretty picture," framed and lined for the public to fawn over. Art documents events from the past, aids in scientific discoveries, and captures and encapsulates both cultural history and human emotions. Through pigment and ink, oil and acrylic, marble and iron, art pieces serve as time capsules, heavy with information from the moment they were created. Brimming with historical significance, it is of the upmost importance to preserve and maintain pieces of art for future generations.
Art conservation is a blanket term that refers to the preventive and preservative care of pieces of art. Adopting an interdisciplinary approach, conservators ultimately aim to preserve the cultural heritage carried through art for future generations to enjoy. Overall, conservator-restorers are held accountable for a variety of responsibilities, such as the examination of pieces in need of repair, research on potential treatment methods, and the implementation and corresponding documentation of the techniques utilized. These processes differ depending on the piece; various factors, such as media (type of material used, such as clay or pencil) and type of artwork (such as sculpture or painting), alter how problem areas are addressed . In order to mitigate discrepancies in the treatment procedure, various institutions, such as the European Confederation for Conservator-Restorers' Organization and the American Institute for Conservation of Historic and Artistic Works, have created "codes of ethics" that clients and conservators are expected to uphold. Typically conservators are expected to implement minimally intrusive techniques, maintain the art's physical integrity, and respect the cultural significance of any object in question .
These overarching guidelines, as well as the ultimate goals of art conservation, are extremely fluid; they are in a perpetual state of evolution and revolution given the rapid advancements being made in the world of technology. Conservation practices have been around for centuries, shifting and warping in correlation to spikes in technological breakthroughs. For instance, attempts at preserving Michelangelo's Sistine Chapel began during the artist's lifetime. Cracks in the ceiling caused large areas of the fresco to be affected by water damage and saltpeter. In order to conceal these imperfections, artists would glaze over the affected areas with linseed oil, making the stains transparent. Moreover, as decades passed, the colors of the Sistine Chapel gradually grew darker and darker, and numerous "quick-fixes" were implemented to counteract the increasing level of grime. In 1713, Greek wine was applied to the walls and, years later, thick layers of varnish. All of these different techniques ultimately failed to completely restore the Sistine Chapel, even though they were considered to be "state of the art" at the time they were used. In 1981, a conservation-restoration project was commissioned by the Vatican. After detailed research on the pigments and layers of accumulated dirt, scientists were able to remove centuries worth of old varnish, soot, water damage, salt buildup, and remnants from past restorative attempts, with a various assortment of weak solvents and distilled water (see Figure 1) . Furthermore, armed with modern day knowledge regarding environmental factors, conservators installed regulatory equipment for the purpose of monitoring humidity and temperature levels. Ultimately, scientific knowledge and conservators' ability to treat artworks are both integral components of art conservation.
Why it is a Necessity
While the advent of technological advancements has undeniably provided aid for the art conservation movement, said advancements also contributed to the degradation and wear on many pieces as well. Exposure to chemical pollutants, extreme temperatures, humidity, excessive light or radiation – all environmental factors that have been exacerbated due to global climate change and mankind's carbon emissions – have heavily damaged many works of art . Both artificial and natural light can cause photo-oxidation or even color fading. Moisture in the air can also cause damage depending on the type of art. For example, high amounts of moisture can react with metals to cause corrosion or can react with plant fibers in textiles to form acids . Moreover, paintings and drawings are largely affected by biodeterioration- microbial breakdown- due to various fungi and bacteria growth, which can be promoted by moisture in the air. These organisms obstruct the view of the image, discolor pigments, and structurally destroy the paper or canvas . The effects of air pollutants, in particular, contribute to the darkening of various types of pigments; hydrogen sulfide gas, for instance, reacts with materials and inks containing copper to form copper sulfide, which is an inky bluish black color . This is a prevalent problem when it comes to buildings . Sulfur dioxide, another prominent air pollutant, reduces the compounds in the original red pigment, leaving behind darker, heavier colors; ; for example, the sulfur dioxide in Naples has blackened the frescoes of Pompeii by reducing the red hematite (Fe2O3) to the darker magnetite molecules (Fe3O4) [6, 9]. As all of these factors combined have the potential to cause irreversible damage to any given piece, it is of the upmost importance that conservators' not only work thoroughly, but efficiently as well.
Secondly, as illustrated in the example of the Sistine Chapel above, sometimes an art conservator's job consists of fixing mistakes and/or damage that they caused. Poor handling and incomplete, inadequate, or outdated conservation jobs all create the potentiality for malicious effects to occur . Again, as art conservation treatments are updated in response to technological advancements, there are always bigger and better techniques being developed.
Techniques Used to Remedy the Wear of Time: The Science behind Conservation Processes
Generally, treatment will vary depending on the type of damaged object, whether it is a ceramic, furniture, sculpture, bronze, or oil painting. Multiple conservation techniques are available to remove damaged varnish, kill harmful microorganisms, retouch faded or damaged paintfilms, and even determine the precise location of the damaged layers.
In spite of the new techniques that are constantly being developed and tested, there are a few "old world" conservation practices that are still highly effective when repairing paintings. Since the 19th century, organic solvents – carbon-based compounds – have been used for cleaning paintings and removing old and darkened varnishes . Since organic solvents are hydrophobic, they are capable of solubilizing damaged hydrophobic varnish or paintfilm, allowing those damaged compounds to be removed. Moreover, these solvents are further utilized in order to clean chemicals, dirt, and smoke build-ups from the painting . Typically during the conservation process, some of the varnish will be left on the painting before applying the solvent in order to prevent the organic compound from damaging the original paintfilm . However, if the original paintfilm of a painting is damaged, then retouching of the paint is necessary; in this process, known as "reversible restoration," after removing the top layer of damaged varnish, the conservator will apply a new layer of varnish before retouching any paint. This method prevents the integrity of paintings from being violated and allows the retouching of any piece to be reversed since removing the layer of newly applied varnish will also remove the layer of newly added paint, thereby allowing the conservator to return the painting to its original state in case of an error during the retouching process .
Organic solvents are not the best conservative technique for all art forms. For example, solvents applied on wall paintings can spread through pores in the wall, instead of simply solubilizing damaged varnish or paint . Furthermore, the support used for wall paintings may not be composed of solely hydrophobic compounds, making it more difficult for organic solvents to solubilize and remove such damaged compounds. Organic solvents that penetrate the paint layers can also cause undesired swelling or leaching of those layers .
While organic solvents can have harmful effects on the original artwork, other techniques are being developed to clean yet preserve art pieces. Instead of liquid solvents, responsive gels – gels that can respond to external electrical, mechanical, thermal, light-induced or chemical stimulation– are being used to remove varnish and grime . These gels contain a mixture of modified pure solvents, enzymes, and other compounds with the necessary cleaning capabilities. The advantage of these gels stems from how they localize the solvent and reduce the risk factor regarding the permeation of underlying paint layers. Furthermore, when external stimulation is applied to the gels, they convert into liquid form allowing them to be removed easily after the cleaning process. This transition from gel to liquid allows responsive gels to carry out their cleaning function without causing any damage to the artwork .
Since 1980, three main types have been developed: rheoreversible gels, magnetic gels, and "peel"-able gels. Each possesses unique strengths: rheoreversible gels can switch into liquid form with chemical triggers, magnetic gels act as sponges to absorb accumulated filth, and "peel"-able gels are highly effective in dissolving old coats of varnish .
Despite the advantages that gels offer over organic solvents, there are still disadvantages to the use of these gels. Some of the unwanted varnish or layers are insoluble to the solvents contained in the gels; as a result, the gels would be unable to solubilize and remove those insoluble layers. Furthermore, like organic solvents, the use of gels still requires direct physical contact with the art piece, leaving open the possibility for mechanical damage to the art .
Another revolutionary practice was founded at the crossroads of etymology and conservation. Cellular biologist Robert Koestler, employed by the Metropolitan Museum of Art, works with scanning electron microscopes to analyze the effects of biodeterioration. Koestler developed a technique to suffocate organisms such as termites or Penicillum found on various artworks through prolonged exposure to inert gases within sealed containers. The basis of his technique is to remove any oxygen from the immediate atmosphere of organisms that contaminate various art items. He sealed art pieces in large Mylar bags along with small packets of iron (II) oxide. While the iron (II) oxide scavenges any oxygen in the bag, Koestier would create a hole in the bag and use a tube to displace the oxygen with humidified argon; argon is heavier than oxygen, thus easily expelling the oxygen from the container without affecting the physical integrity of the art. Since various microorganisms have the ability to withstand oxygen deprivation for several days or weeks, this entire contraption is used for a few weeks in order to kill all living organisms living on the art items .
Courtesy of cleanLASER
Amongst other widely effective processes developed in recent years, lasers are used to clean white marble friezes, such as those on the Parthenon. The removal of pollution contaminants from stone is typically done via ablation at very specific wavelengths. Researchers found that exposing the marble to two wavelengths-- infrared and ultraviolet--at once, as opposed to a single one, allows for multiple levels of build-up removal . Lasers, like inert gases, are ideal mechanisms for restoration due to the fact that they leave the underlying surface of the object unaltered, require no direct physical contact with the artwork, and offer the conservator great control and precision during the cleaning process (see Figure 2) [17, 19]. However, lasers are not useful for all types of artwork. While white marble and stone structures have been successfully cleaned using lasers, laser cleaning for oil paintings is widely impractical and even dangerous due to the higher chemical complexity and multi-layered nature of paintings .
X-Ray Absorption Spectroscopy
X-ray absorption spectroscopy (XAS) can be used to detect the precise location of varnish and oxidized layers on an art work. While XAS does not provide a mechanism of actually cleaning those damaged layers, it allows conservators to determine chemical changes that have taken place on a variety of materials, such as glass, ceramics, metal, paintings, and wood [20, 21]. During XAS, objects, in this case art samples, are exposed to synchrotron radiation (SR), which encapsulates all the wavelengths of the electromagnetic spectrum . The radiation emitted towards the sample, known as incident x-rays, have a certain intensity value. Once the rays hit and interact with the sample, some of the radiation will be scattered and some will be absorbed, leading to a decrease in the intensity of the radiation that passes through the sample. XAS assesses this change in intensity to determine the absorption coefficient of the sample. Different atoms and compounds in the sample may absorb radiation to different extents, all of which are markers—"fingerprints"—for identifying the presence and concentration of specific chemicals in the sample [20, 22]. Furthermore, XAS has the profoundly useful ability to enable conservators to determine the specific layer of a pigment on an oil canvas that is suffering from discoloration or damage . While the analysis and information gathered will differ depending on the media analyzed, XAS yields highly effective results. Conservators can obtain valuable information on degradation reactions, chemical composition, and even the methods used to physically craft these art pieces centuries ago. Despite its valuable functions, XAS also has the potential to cause damage to art pieces since the radiation can cause blackening of the sample, photoreduction, or a decrease in the oxidation state of the chemicals in the art piece.
In order to decrease the frequency at which certain pieces need to be treated, most museums have implemented monitoring systems in order to regulate environmental factors that affect the chemical composition of paintings and sculptures. Factors such as light, humidity, and pollution all have the ability to affect the materials in a piece of art. As a result, museums implement a variety of methods to reduce these harmful effects. For example, many museums reduce light damage by using dimmer lights, filtering out ultra-violet light, and placing filters on artificial light sources to reduce the light intensity. To reduce the humidity in the air inside museums, devices known as thermo-hygrometers are used to monitor the amount of moisture present in the air. To monitor air pollution, sampling tubes are used and analyzed in laboratories for the presence of chemical pollutants. For instance, during the summer of 2011, the Metropolitan Museum of Art tested a set of sensors manufactured for the sole purpose of mitigating detrimental effects from environmental damage. These machines can measure an abundance of factors, such as temperature, humidity, air flow, and light exposure; the specific climate surrounding any given object in a room can be closely monitored in order to maintain optimal conditions for art pieces .
Controversy Regarding the Implementation of Conservation Techniques
The manner in which a piece a treated, if at all, is largely dictated by the International Code of Ethics, in addition to local or regional practices. While there may be slight discrepancies in attitude towards addressing damaged pieces between nations, the global set of standards prevents drastic differences from occurring. This standardization is paramount in minimizing the potential for the formation of blatantly contradictory conservation methods.
However, regardless of how detailed and specific said ethical lists are, the extent to which pieces are "fixed" is an extremely controversial issue. For instance, the highly- publicized cleaning of the Sistine Chapel, as discussed in the sections above, remains one of the most heavily debated conservation projects of this time period. After the application of solvents and detergents, the colors of the Chapel appeared intensely bright—a factor which has been widely criticized. During the restoration, some of the chemicals washed away a top layer of charcoal that Michelangelo integrated into the frescoes in order to create depth. Without this layer, shadows have become unsaturated and have disappeared altogether in some areas . Consequently, many argue whether the project went too far in its cleaning endeavors. This project entailed mostly restorative processes rather than conservative processes; while restoration often entails significant changes in the appearance of the artwork, conservation mostly involves cleaning and preservation of the art piece's appearance. Currently, conservators aim to complete their jobs while maintaining historical and aesthetic integrity in order to prevent such critique from erupting .
Historical Relevance and Significance
Ultimately, in spite of its drawbacks and proclivity for creating controversies, conservation plays a vastly significant role in modern day society. Firstly, it is of the upmost importance to museums. Through the implementation of various scientific techniques, such as those discussed above, not only are conservators able to clean and maintain artwork but they are also able to obtain knowledge regarding the chemical compositions and historical contexts of objects. In turn, museums are granted the ability to determine the authenticity of both newly acquired and long-owned pieces. The art market, exchanges between galleries, and a museum's overall reputation are heavily impacted by the authenticity of artwork. As such, conservation's role in the art world is undeniably multi-dimensional .
As scientific knowledge continues to expand and technological advancements continue to develop, one would expect specialists to enhance or even perfect the practice of conservation. However, mankind's abilities in this field are perpetually tested by the frequent introduction of new factors that cause degradation. Technological advancements are often accompanied by come an increase in damage-inducing agents, such as pollutants . Furthermore, what degree of restoration and repair is acceptable remains ambiguous. Since many conservation techniques result in undesired damage to the artwork, these techniques are constantly undergoing changes and advancements. All in all, science and art conservation are interconnected fields with substantial room for improvement and enhancements.
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