The Use of Infra-Red And Ultraviolet Light

The Chemistry of Art > 2. The Structure of the Atom and Colours > The Use of Infra-Red And Ultraviolet Light >

The use of infra-red and ultraviolet light in the analysis and identification of pigments and their chemical composition

Infra-red Light:

    • Extends from wavelengths of 700 nm to 1 mm
    • Near IR radiation lies closest to ‘red’ part of visible region and far IR radiation lies closest to microwave region
    • In IR region, many organic polymers are excited by and are able to absorb energy of varying wavelengths, making IR light as tool to analyze molecular structure of organic paint films.


    • Good for detecting painting under-drawing wherein artist has used graphite pencil, charcoal or black ink since carbon absorbs IR radiation and does not reflect it back
    • Detects presence of copper-containing green pigments since these pigments also absorb IR radiation
    • IR radiation penetrates pigments and reflects from white ‘ground’

Example:  Titanium Oxide, Cadmium Sulphide, mercury sulphide vermillion
Ultraviolet (UV) light:

    • Absorbance plotted as function of radiation wavelength
    • Unit of wavelength: nanometer (nm)
    • Contains enough energy to break the covalent bonds of most organic molecules


    • UV light (in tandem with water and oxygen) are used to induce slow degradation of several organic polymers which include polymers used  to bind paint film
    • Useful for detection of chemical changes in sketches (Carbon) and paint over attempts
    • Helpful in the identification of pigments containing Cu and ZnO (fluoresces in UV light)