From analysing ancient textiles from Jordan to conserving a Hogarth or aJack B. Yeats, art and archaeological conservation offers an interestingscientific challenge. Dick Ahlstrom reports
Chemists are usually associated with test tubes and Bunsen burners, but sometimes their work includes 1,500-year-old textiles and the preservation of great art. Scientists involved in archaeological chemistry handle these exotic activities.
Dr John Fields is a specialist in the use of science in art and archaeological conservation. He is a chemist in the environment/heritage section of the State Laboratory in Abbotstown, Dublin, and has worked on unusual subjects recently.
He joined the State Laboratory about a year ago from the British Museum in London, where he worked in the conservation lab. "I work mainly on organic objects," he says. This includes paper, textiles, paintings, wood - "anything that is organic".
Variety is at the core of this work, along with the application of scientific techniques to achieve specific goals. Each object presents a unique challenge, he says. It involves the preservation or scientific analysis of ancient artefacts, modern paintings and in a new research project, the chemical analysis of a Viking artefact dug out of the ground recently in Waterford.
It requires the use of the latest analysis equipment, such as X-ray fluorescence, gas chromatography and high-performance liquid chromatography. Behind this, however, it still involves an understanding of chemistry and the use of this in conserving our archaeological heritage.
His latest research project is a joint effort with the National Museum and involves a Viking artefact recovered some months ago in Waterford. "The piece we are looking at is a cone-shaped object," he explains.
It is silver and has a spiral of silver coming out of the top. A crumbly, black, waxy substance holds the spiral in place and the museum wants to know what this material is - information that may help in understanding how the artefact might have been used.
Dr Fields's previous project was a joint study with the National Gallery of Ireland, and related to drawings and sketches by Irish artist, Jack B. Yeats. Abbotstown colleagues involved in the work included Conor Murphy, Joe Foley and William King, the head of the environment/heritage section at Abbotstown.
Jack B. Yeats frequently used wax crayon and colouring pencils to sketch out rough work for later paintings in oil. The gallery was concerned that some of its holdings might be incorrectly labelled, as handling requirements for crayon and pencil are different. It asked Abbotstown to find test methods to confirm the materials used on a given sketch.
It tested contemporary crayon and pencil on paper samples provided by the gallery and used several analysis systems to study them, focusing on stearic and palmatic acid content typical of crayon. "We couldn't tell the difference, unfortunately," he adds, showing that science doesn't always have the instant answers.
He had better luck with two projects while at the British Museum in London. One involved a burial cloth from the early 5th century recovered in Jordan and the other a study of deterioration in stored drawings from artists, such as William Hogarth, held by the museum.
The Jordanian textiles were recovered five years ago after a joint "dig" involving the museum and Jordan. "They were quite a rare find," says Dr Fields. The museum agreed to conserve them but also analysed the dyes employed to colour them, using liquid chromatography to analyse a small sample dissolved in acid for its content.
"We looked mainly at the reds and blues," he explains, establishing indigo as the probable blue and the red a mix of alizarian and purpurin. Signs of purple dye on the textile were a surprise given the cost and rarity of purple in ancient cloth, but the team found it was a mix of the less expensive blue and red.
The other project related to the use of "iron gall ink" in drawings by artists, such as William Hogarth, in work from the early 1700s. "Iron gall ink is one of the materials artists would use but it is very acidic," says Dr Fields.
It literally dissolves holes over time, but the museum, 30 years ago, developed a treatment using barium hydroxide to neutralise and stabilise the ink. The project involved an assessment of how well this treatment worked using X-ray fluorescence to measure barium metal content. Acidity was also checked.
The ph 30 years ago on one Hogarth drawing was 3.9 and after treatment was near neutral at 7.6. The research showed acidity of the ink is rising again and now stands at 5.0. "They are reverting back to acidity but not as quickly as untreated drawings," he says.