From Newman (1977, p. 74):
Glass … is colored by (a) impurities in the basic ingredients in the batch (e.g., bottle glass), or [by] (b) techniques of coloring transparent clear [i.e., colorless] glass by [the following] main processes: —
- Use of a metallic oxide … in the batch to impart a color throughout;
- Use of a substance in a colloidal state (e.g., gold ruby glass, with microscopic particles of gold); and
- Use of embedded particles of colored glass material (e.g., aventurine glass).
Colors shown in this folder were produced by the first technique, above. The following list indicates the metallic oxides used to produce various colors, from The Corning Museum of Glass (note 1) and Matthews (note 2):
- Antimony = yellow
- Cobalt = dark blue
- Copper = light blue or green; shades of red (in a reducing atmosphere)
- Iron = various shades of green
- Iron + Sulphur = amber
- Manganese = purple
- Selenium + Cadmium + Sulphur = red
- Silver + Sulphur = yellow (especially as a stain)
- Titanium = shades of yellow-brown
- Uranium = fluorescent yellowish green or greenish yellow
- Antimony + Lead = opaque yellow
- Tin = opaque white
“The resultant color from any metal oxide depends on the nature of the glass itself [i.e.lead potash, soda lime, etc.] and the purity of its ingredients and also on the furnace conditions, as to the the degree of heat or the existence of a reducing atmosphere” (Newman 1977, p. 197).
A modern rose bowl, purple (amethyst) cut-to-clear, that uses a universal shape and international motifs that have antecedants in the nineteenth century. As a result, the bowl’s date and place of manufacture cannot easily be determined. Lead glass. 12-pt star on base. D = 6″ (15.2 cm), H = 5″ (12.7 cm), wt = 2 lb (0.9 kg). Sold for $100 in 1990.
1. The CMG sells, in its gift shop, packets of colored glass lozenges (that look like after-dinner mints) made from several of the metallic oxides listed here.
2. Matthews, Thomas, 1995: Color overlayed (sic) cut glass, in AMERICAN CUT GLASS IN COLOR, Special Edition No. 1 of The Hobstar, pp. 5-7, Feb.