Glass Color Process

In order to understand more about how glass is colored, it is important to understand the ingredients used in the glass making process.

Soda-lime glass is the most common type of glass. It has many strong points, such as being inexpensive, reasonably durable and very workable. It is used for about 90% of all manufactured glass objects (bottles, drinking glasses, windows, light bulbs, containers etc.).

Soda-lime glass is made by melting a mixture of the following elements at high temperatures:
  • 75% SILICA (silicon dioxide), the primary constituent of sand
  • 15% SODA (sodium oxide), serves to lower the temperature at which silica melts
  • 9 % LIME (calcium oxide), acts as a stabilizer for the silica
  • 1% smaller amounts of various other compounds
When it is not very thick, ordinary soda-lime glass appears to be colorless. In thicker pieces, due to iron oxide impurities, the glass takes on a green tint.

Early glass makers had no control over the color of their glass products. Through accident and experimentation, glass makers learned that adding certain substances to the glass melt would produce different color results, while other substances would remove color from the finished project.From this point on, the evolution of the many colors of glass began.

The recipe for producing colored glass usually involves the addition of a metal to the glass in its molten state. This is often accomplished by adding powdered oxide, sulfide or other metal compounds.
The high value of some metals used as glass colorants makes certain colors of glass very rare, as they were not heavily produced.

Below is a set of glass color info cards that we have created to give a basic understanding of how certain glass colors are achieved: