After taking a sample of paint or varnish, Fourier transform infrared microscopy (FTIR) can help to find out what materials are present. In paint, it can identify the pigments used. It can also show whether the binding medium is oil or a type of protein, such as egg or glue.
FTIR uses infrared radiation – a portion of the electromagnetic spectrum just beyond visible light – to analyse the materials.
The molecules present in a sample absorb infrared radiation at specific wavelengths, producing a characteristic ‘fingerprint’ for each class of material.
An FTIR (Fourier transform infrared microscopy) microscope at the National Gallery