Gas chromatography–mass spectrometry (GC-MS)

GC-MS is a useful method for identifying the binding medium used to hold all the pigments together.

A good binder must work with the pigment to work well off a brush, stick to the painted surface, and retain colour over time. Different artists use different materials to do this job so identifying the binding medium can help to determine who the artist was.

In gas chromatography (GC) the paint sample is placed in a solution. This solution is then injected into a stream of gas, usually helium. This gas in turn is forced through a thin heated tube. It is here the sample is broken into its component chemicals.

A mass spectrometer (MS) is then analyses these chemical components. The individual molecules are bombarded by a stream of electrons which causes them to break apart into fragments. The mass of these fragments is then measured and the resulting graph is analysed to identify exactly what materials are present.

The GC-MS method was used to identify the presence of Bakelite in the paintings of Han van Meegeren.