In a paper published today (free registration required) in the latest edition of Measurement Science and Technology, Roberto Olmi and his team at the Institute of Applied Physics in Florence demonstrated a new technique to evaluate the “health” of frescoes. Frescoes face two main hazards: moisture from the atmosphere and salts in the plaster of the wall on which Renaissance masters made their original paintings.
Their tool, called SUSI (Sensore di Umidita e Salinita Integrato) can measure salinity and humidity up to a depth of 2 cm below the pain coating.
“At the beginning of twentieth century, for example, in order to save the paintings a technique used by restorers here in Italy has been to detach the whole thing from the wall and mount it on a wooden board called a Masonite support. An early detection of moisture behind the paintings using SUSI would have avoided such an invasive and dangerous procedure” said Olmi.
Moisture can damage a fresco in two ways. Water flows to the surface and evaporates, taking bits of the paint with it. Water can also transport soluble salts from the plaster of the wall to the surface, where they crystallise. Eventually the painting whitens and begins to fall off the wall. Until now, measurements of the water and salt content of a fresco have only been possible by taking samples of the paint or drilling holes through the painting to obtain a sample of wall plaster. Paradoxically, just to assess a painting’s condition, researchers had first to damage it a little. The new SUSI tool could now offer researchers the opportunity to obtain the data they need without damaging the fresco.
The surface of the painting is scanned with a sensor device the size of a video camera. Water and salt molecules in the plaster absorb the microwave radiation: then the scanner registers the returning signal and the computer determines the level of moisture or salinity.
The tool has been under development for the last two years and so far has been tested on the field on such frescoes as the Paradise Wall of the chapel of Santa Maria Maddalena de Pazzi, painted by the studio of Giotto; and the frescoes in the cloister of St Antonino at the Convent of St Mark, painted by Bernardino Pocetti, both in Florence.
Ultimately, this kind of device could be used for other kind of work of art such as ceramics and, with further development, paintings and parchments. Currently, those last two mediums are too thin to be evaluated by SUSI.
July 17th, 2006 | General Science