The Relationship Between Absorption and Reflectance Spectra

The Chemistry of Art > 2. The Structure of the Atom and Colours > The Relationship Between Absorption And Reflectance Spectra >

The relationship between absorption and reflectance spectra and the effect of infra-red and ultraviolet light on pigments including zinc oxide and those containing copper


  • Absorption:
    • Appears as black spectral lines within full spectrum
    • Percentage of light absorbed at each wavelength
    • Signifies which photons have been observed and hence which frequencies of visible light have been absorbed
  • Reflectance:
    • Percentage of light reflected at each wavelength
    • Substance exhibits colour complementary to that color of absorbed particular wavelength.

Effects of Infra-red (IR) lights on selected compounds/substances:

  • Zinc oxide changes from white to lemon yellow (returns after cooling)
  • Red Copper (I) oxide changes to black Copper (II) oxide
    (permanent change due to substance breakdown)

Effects of Ultraviolet (UV) on selected compounds/substances:

  • Zinc oxide (ZnO) fluoresces as pale yellow under the presence of UV light
  • Green malachite (CuCO3 . Cu(OH)2 ) fluoresces dirty mauve colour