It is the aim of this project to continue the use of artists' materials in this way and to link it with piezoelectric quartz crystal (PQC) technology. The useful property of piezoelectric quartz crystals is that they allow a binding event e.g. coating to the gold substrate to be converted into a measurable signal, for example resonance frequency changes. This offers many applications and an increasing number of publications has illustrated these phenomena.

The principle is based on the piezoelectric properties of materials such as quartz crystals. Under an alternating electrical field mechanical vibrations of the crystal were observed and ultrasonic waves were generated, the quartz crystal vibrating near its resonant frequency. When it was included in an appropriate electronic circuit, the measured oscillation frequency was close to the resonant frequency (e.g 10MHz) and the generated wave amplitude reached a maximum. Thus a modification of a physical characteristic of the resonator, for example the global mass or the thickness led to a resonator frequency variation. Typical shifts in the resonant frequency of the crystal are of the order of 10kHz for coatings of micrometer thickness and nanograms in mass.

Coated piezoelectric quartz crystals (typically AT cut) have been used for the last 10 years also as air pollution detectors and testing of various coatings has been performed for sensitivity to SO2, ozone, NO2, NH3 , H2S and other hazardous organic vapours. Potential CO2 sensing has also been recently reported. Further shifts occur with alterations in the physicochemical properties of the coating as a result of adsorption of molecules from the environment. In a previous EU project poly(ethyleneimine) coated crystals were used for localised RH measurement.

We will use the basic design (supplied by QuartzTech technology) to construct a sensor array based on eight quartz crystals. The sensor chamber will incorporate eight interchangeable piezoelectric quartz crystals. The instrument will incorporate sample classification programmes that implement principal component analysis (PCA) and discriminant function analysis (DFA) routines. Classification is based on the nature of molecular interactions e.g. dispersion forces, dipolar polar interactions, dipole interactions and hydrogen bonding. Each sensor coating is chosen to optimise specific type of interaction. In the case of our sensor array we would use quartz crystals coated with artists' materials. We would start with varnish and proceed with tempera based coatings.

We are interested in (1) assessing damage from the integrated response of the synergistic action of environmental factors (2) possibility of coatings specific to the action or more sensitive in their response to certain pollutants. After the data processing and identification of locations of high damage potential, suggestions for improvements, either to the general environmental control or a particular microclimate surrounding an artwork, would be given.