Frescoes are works of art that were directly painted onto walls
during the Renaissance, which ran from the late 1300s to the
start of the 17th century. Found in churches and chapels across
Italy, these paintings are continually being attacked by
moisture from the atmosphere and salts in the plaster of the
walls. Knowing the moisture and salt content is important for
restorers so that they can decide on the best way of saving a
painting. Until now, however, this was only possible by drilling
holes through the painting to obtain a sample of the plaster.
Now, Olmi and co-workers claim to have found a solution to this
problem. Their technique involves scanning the surface of the
painting with a portable sensor device that fires microwaves at
the wall. If water and salt molecules are present in the
plaster, they absorb the microwaves and send a signal to a
computer that then determines how much moisture or salt is
present. This is calculated by measuring the material’s
dielectric constant, (a material's ability t