Glass Colorization

Color can distinguish a glass container, shield its contents from unwanted ultraviolet rays or create variety within a brand category. Color can be obtained by simply adding small quantities of different oxides:
  • Chromium (for green)
  • Cobalt (for blue)
  • Nickel (for violet/brown)
  • Selenium metal (for red)

The raw materials used in commercial glass making contain iron oxide as an impurity, which imparts a yellow/green color to the glass

To offset the yellow/green when making flint (or “colorless”) glass, other colors are introduced by adding selenium (for red) and cobalt (for blue) in proper proportions to yield a gray glass that appears colorless, hence the term “decolorization.”

Glass Colors

Amber Glass
  • Amber is the most common colored glass, and is produced by adding together iron, sulfur, and carbon.
  • Amber is a “reduced” glass because of the relatively high level of carbon used. All commercial container glass formulations contain carbon, but most are “oxidized” glasses.
  • Amber glass absorbs nearly all radiation consisting of wavelengths shorter than 450 nm, offering excellent protection from ultraviolet radiation (critical for products such as beer and certain drugs).
Green Glass
  • Green Glass is made by adding non-toxic Chrome Oxide (Cr+3); the higher the concentration, the darker the color.
  • Green glass can be either oxidized, such as Emerald Green or Georgia green, or reduced, as with Dead Leaf green.
  • Reduced green glass offers slight ultraviolet protection.
​Blue Glass
  • Blue glass is created by adding cobalt oxide, a colorant so powerful that only a few parts per million is needed to produce a light blue color such as the shade used for certain bottled waters.
  • Blue glasses are nearly always oxidized glasses. However, a light blue-green glass can be produced using only iron and carbon and omitting the sulfur, making it a reduced blue.
  • Creating a reduced blue is seldom done because of the degree of difficulty in fining the glass and controlling the color.
  • Most colored glasses are melted in glass tanks, the same method as flint glasses. Adding colorants to the forehearth, a brick lined canal that delivers glass to the forming machine of a flint glass furnace, produces oxidized colors.