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Colored
glass
The color of a transparent material such as glass is due to the
absorption of light at certain wavelengths in the visible spectrum
(350-700 nm). There are several types of absorption:
- Electron transfer between cations and anions. Depending on the
ions used, absorption can occur in either the visible or non-visible
spectrum. Electron transfer between FeIII+ and OII-
corresponds to ultraviolet absorption. The replacement of OII-
by SII- moves the absorption band into the visible range,
towards 410-420 nm. This produces an amber colored glass on which
are based most of the current colors used in bottles.
- Electron transfer from one electronic layer to another within
the same cation. The wavelength of the absorption depends on the
cation and the glass matrix. For instance FeII absorbs
around 1000-1100 nm and therefore gives the glass a blue tint.
- The interaction of light with specific particles blended within
the glass: this produces for example copper ruby red in which small
aggregates of copper CuI and Cu0 can be formed
by heat treatment. This is also the case for silver-yellow or gold-red.
- The interaction of light with small crystals formed during cooling:
this renders the glass white as a result of light diffusion.
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