Get A Reaction! aka The Chemistry of Glass Colors

Glass is everywhere. It is a seemingly straightforward material. Surprisingly, however, glass is actually very complex, and understanding this complexity and the chemistry behind it is critical for a glass artist.

Let's Talk Light

Color in glass can transform itself. It can reflect light and transmit light, or both at the same time. When lit from the front, we see only the colors of reflected light, similar to most other media. When glass is lit from the back, we see transmitted light colors or both reflected and transmitted colors.

The transparent, translucent, or opaque nature of glass further changes the color you see.

Let's define these terms:

• Transparent glass refers to colored glass mixed with clear, also called Cathedral glass.

• Translucent or semi-opaque glass, usually referred to as opal, interferes somewhat with the ability of light to pass through it.

• Opaque glass does not allow light to pass through it all, only reflecting it.

On top of this, the thickness of a piece of glass affects how it transmits light and can modify the value of transparent and translucent glass. Thickness also affects the saturation of color. For example, the same piece of red glass can appear deep red if it is thick, or orange or pink when very thin.

Now For The Chemistry

The colors in glass, just like the colors in ceramic glazes, are made by combining chemicals. Let's take red for instance. A beautiful pure red is a difficult glass color to achieve, and as a result, the reds often seem a bit orange. This is because pure red glass typically has gold in it, driving the cost extremely high. Other colors like coral, pink, and shades of purple also contain gold, which in turn makes artwork created with these colors more expensive.

The chemical composition of glass, when fired can dramatically influence the color. Copper, which is found in most turquoise glass colors, reacts with the sulfur in some warmer glass colors, such as red and orange. When heated to fusing temperatures, the reaction of the copper-bearing glass with the sulfur-bearing glass creates a third color where they touch, either a brownish color or gray, depending on the chemicals in the glass.

Finally, some glass will look pale or colorless in the cold sheet form, but “strike” or mature to a much different color when fired. Striking colors can vary, depending on temperature, atmosphere, and heat history.

So if we seem hesitant when you ask us about a custom order using different colors, it's because we are considering the potential reaction and final outcome when certain glasses are combined.