More than dust on the surface: on Jean-Etienne Liotard's pastels

Pastel is a paradoxical medium. It is the most fragile of materials—essentially dust rubbed on a surface (usually paper). It is easily disturbed and impossible to fix without altering its character. Yet when it is well cared for, pastel is a stable medium, lacking as it does the amount of binders, stabilisers, driers and adulterants that cause oil paints to discolour. The colours of 18th-century pastels are sumptuously rich and vivid compared with darkened oil paintings of the period.The