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The science of art conservation

Ask a science student about their career goals, and you’re likely to find some prospective teachers, researchers or those expecting to work within the chemical industry. One thing you might not expect is the aspiring art conservator. It may be a surprising profession when it comes to science students, but the skill and technology required for successful art conservation means that there is a real need for analytical and material specialists.

Art conservation has long since been a challenge to maintain cultural heritage. Restorations of the Sistine Chapel date back to the 16th century, where treatments to the frescoes used linseed and walnut oil. Fortunately, advancements in analysis and restoration techniques have revolutionised the field, leading to more efficient processes and a reduction in unwanted damages.

The work of a conservator starts with a detailed examination of the artwork itself. The environment in which it is stored and the materials used to originally create the piece can vary greatly, so a true analysis in an attempt to figure out the underlying reasons for deterioration requires real analytical skill. Multiple factors may contribute, ranging from temperature, humidity, light exposure and poor maintenance techniques.

An initial analysis will likely consist of x-rays to determine elemental composition without destroying the object. Currently, x-ray fluorescence analysers are able to identify a range of materials including pigments, ceramics, glass and metal. They can also be used to distinguish between the original materials and those left behind from previous conservation processes.

Raman spectroscopy is also used to determine the composition of varnish. In paintings, a layer of varnish is sometimes applied over the paint layer to protect the piece. Over time, the varnish can undergo oxidation reactions and become discoloured. In Raman spectroscopy, energy is absorbed by the material and radiated at a different frequency, allowing characterisation of the varnish. Once the identity of the varnish is known, an appropriate solvent can be identified to remove discoloured varnish layers without any changes to the painting underneath.

Selecting an appropriate treatment for the artwork and performing it without causing damage is another feat altogether. Initial treatment may involve the removal of dirt using aqueous solutions. A variety of pH-controlled organic solvents may also be used. These can be applied using gels which slowly release the solvent to avoid swelling damage that can be seen when free solvent is used. Despite this, the use of gels is somewhat problematic, as, after cleaning, the gels need to be scraped out of cracks in the painting for complete removal which can result in damage.

The use of nanoparticles is considered to be a more controlled and more effective method of cleaning. Nanoparticles are smaller than the paint particles, meaning that they can slide between them for a deeper clean. Laser cleaning is also a popular method used to remove surface deposits. Using controlled energy pulses, a laser can remove unwanted materials whilst leaving the painting or sculpture underneath unharmed. In 2010, this laser technology was used for the removal of thick deposits of white calcium carbonate in a catacomb in Rome. This process led to the discovery of the oldest known images of the apostles Peter and Paul, dated back to the fourth century, which would have otherwise remained hidden.

Of course, the restoration process is not always successful. Technical failures in distinguishing between dirt and the materials used in the art can lead to unwanted consequences. The restoration attempt on The Virgin and Child with St. Anne, an oil painting by Leonardo da Vinci, led to controversy between critics who claimed that the painting became far lighter than the artist intended. It is evident, then, that care needs to be taken during restoration, and a full analysis must be performed to avoid irreversible damages.

Though advanced and innovative methods of restoration are being researched to avoid such occurrences, critics also argue that the integrity of artwork can be destroyed even by completely successful restoration attempts. Perhaps it was the intention of the artist for the piece to change over time all along.

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