“Art is science made clear” according to American playwright Wilson Mizner. Well, recent research published in Analyst magazine seems to flip this on its head. Using science (or specifically mass spectrometry) to make art clear, Sophie Dallongeville and colleagues successfully identified the biological origins of a glue used to glaze a sculpted Baroque angel.
The angel they studied is one of a pair flanking a 17th century altarpiece in the church of St. Michael of Mondsee in Austria. At first glance the worshipper would have been struck by the heavenly glow of the angels, achieved by the use of an unusual embellishing technique; the application of green lacquer to a layer of silver leaf.
The angels’ glow also depends on the glue used to stick the lacquer to the silver leaf and thus art historians and restorers are keen to identify its biological origins. Ancient texts claim that it is isinglass, a glue made from the swim bladder of a sturgeon, but this has never been confirmed.
Dallongeville and colleagues set out to identify the glue. They expected it to be mostly composed of proteins and so stained a small sample of angel with a molecule that, when bound to a protein, glows under UV light. This confirmed the presence of a thin protein-containing layer between the silver leaf and green lacquer.
To identify the animal origins of the proteins the researchers used mass spectrometry. The technique works by characterising the sequence, or order, of the building blocks – called amino acids - that make up a protein. Because fish proteins will have a unique amino acid sequence that differs from the sequence of other animal proteins, this technique can be used to determine the biological origins of a mystery sample.
The researchers looked for matches for the glue amino acid sequence in a database of known sequences and got several hits: all segments belonging to the fish version of collagen (a major component of nails, skin and bones). The researchers were unfortunately unable to tell which species of fish the collagen came from because of a lack of fish collagen sequences in the database.
The presence of fish collagen in the material proved the ancient texts right - a glue containing fish was used to embellish the angels. Even though we remain ignorant of whether it was actually isinglass that was used, knowing that the glue was made of fish proteins should help restorers to carefully conserve and restore the angels.
This research paves the way for mass spectrometry to identify biological material in other works of art. Because the authors used only a tiny amount of starting material they showed that this technique could be minimally destructive. Hopefully mass spectrometry will continue to be used to aid the restoration of ancient artworks and continue to prove that, contrary to what Wilson Mizner might have thought, sometimes science really can make art clear.
Dallongeville S, Richter M, Schäfer S, Kühlenthal M, Garnier N, Rolando C, Tokarski C. Analyst. 2013 Sep 21;138(18):5357-64. doi: 10.1039/ c3an00786c. Proteomics applied to the authentication of fish glue: application to a 17th century artwork sample.