Deliberate coloration of
glass requires the addition of an appropriate mineral, e.g.
malachite for green, pyrolusite for purple, etc. The crushed
mineral and crushed frit [see Glassmaking]
are mixed together and then heated through to the point of
fusion.(Often, these mixtures have a lower fusion point than
naturally colored glass.)
The glass's color, and its intensity, are dependent
upon the furnace atmosphere during firing. The usual, oxygen-rich
environment (i.e. an oxidizing state) will produce one color
while an oxygen-starved environment (i.e. a reducing state)
will produce another. For example, the iron impurities that usually
color glass aquablue or light green will produce an amber shade
when fused in a reducing environment.
Chigi ms., 15th century A.D.
1) Brill, R.H., 1965: "The Chemistry of the Lycurgus Cup,"
Proceedings of the VIIth International Congress on Glass,
paper 223 ((Brussels: I.C.G.).
2) Brill, R.H., 1988: in Excavations at Jalame, pp. 257-294
and Table 9-6 (ed., G.D. Weinberg: University of Missouri Press,
3) Brill, R.H. and Cahill, N.D., 1988: "A
Red Opaque Glass from Sardis and Some Thoughts on Red Opaques in
General," Journal of Glass Studies 30, 16-27.
4) Brill, R.H. and Schreurs, J.W.H., 1984: "Iron and Sulphur
Related Colors in Ancient Glass," Archaeometry 26, 199-209.
5) Fleming, S.J., 1999: Roman Glass: Reflections on Cultural
Change, Appendix A (University of Pennsylvania Museum, Philadelphia).
6) Henderson, J., 1985: "The Raw Materials
of Early Glass Production," Oxford Journal of Archaeology
7) Weyl, W.A., 1951: Coloured Glasses,
121-131 and 420-432 (Sheffield: The Society of Glass Technology).
8) Whitehouse, D. (ed.), 1990: "The
Portland Vase," Journal of Glass Studies 32, 14-188.