Italian scientists have developed a sensor that bounces rays through frescos to see whether they risk getting discoloured, fading or falling off walls.
The camera-sized sensor is important because it is non-invasive, measuring humidity and mineral content without having to take samples of works.
The new sensor is run across fresco surfaces, sending micro-waves that can penetrate as far as two centimetres.
"Frescoes are threatened by two things: too much humidity and an over-rich mineral content," said Roberto Olmi of the National Research Council's Applied Physics Institute in Florence, which developed the gizmo over two years.
"Humidity can make pigments runny and minerals can crystallise so that the frescos fade or begin to crumble," Olmi told the journal Measurement Science Technology.
The sensor goes under the acronym SUSI, for Sensore di Umidita' e Salinita' Integrato (Integrated Humidity and Salinity Sensor).
A prototype of SUSI was successfully tested on specially prepared samples at Florence's famous art heritage lab l'Opificio delle Pietre Dure.
It was subsequently used on frescos by Giotto and other painters in Florence churches. SUSI is more versatile than first thought.
"For instance, we've used her to gauge the water and mineral content of famous Della Robbia ceramics," Olmi said.
Now the challenge facing Olmi's team is to develop the instrument further to examine archment and canvas, which are too thin for the current version of SUSI to be safely used.
