Use the IR spectrum for different blue dyes to date and identify fakes

This is a nice introduction resource to the use of spectroscopy in industry.

What’s the chemistry?

The precise paints, pigments and varnishes used in a painting can tell art historians a lot about when, where and how it was made, as well as the culture of the time. For example, a paint which looks ‘blue’ to the naked eye could in fact be any one of a number of different blue pigments, perhaps ultramarine, azurite, Prussian blue, Egyptian blue or cobalt blue.

A chemical technique called furier-transform infrared spectroscopy (FTIR) can distinguish between these different blues.

The pigments absorb certain wavelengths of infra-red radiation depending on their structure. FTIR can measure this and produce a characteristic spectrum, a bit like a unique ‘fingerprint’ for a particular molecule.

So FTIR can tell the difference between super-expensive medieval ultramarine and the cheaper modern alternatives like cobalt blue, even if our eyes cannot.

Chemical analysis recently revealed that the background on the National Gallery’s Master of Mornauer portrait contained Prussian blue – a pigment which was unheard of when the artwork was originally painted! Art historians believe fraudsters made the change to convince collectors that the painting was a more valuable piece by the artist Holbein.

You can find out more about the techniques used to solve this mystery on the Learn Chemistry ‘Faces of Chemistry’