Julie Coll

What is Glass?

The explanation can get a bit complicated but I’ll try and keep it simple and not too technical. In science classes we are taught about the three states of matter being gas, liquid and crystalline. Although glass is a solid material it is a type of matter with a non-crystalline or amorphous structure. Glass is neither a liquid nor a solid but shares qualities of both.

Glass is created by heating dry materials to a viscous state and then cooling quickly. (Viscosity is a liquid’s measure of its resistance to flow.) The quick cooling process prevents a regular crystalline structure from forming like with a solid. Instead the atoms get locked in a disordered state like a liquid. So glass has the rigidity of a crystalline solid with the random atom structure of a liquid.


In nature glass is formed in one of three ways. When silicic lavas from a volcano are cooled quickly obsidian is formed. This is also known as volcanic glass. Fulgurite tubes are crusts of glass that are formed when sand is melted by a lighting strike. Fulgurite tubes are sometimes called “petrified lightning”. The third naturally occurring glass is moldavite. It does not contain a crystalline structure but rather a diagnostic pattern of striae and bubbles. Because of this it is believed that moldavite is formed from the outer surface of meteorites that have fused and melted during entry into our atmosphere.

The man made glass that we are familiar with is made by melting silica (sand) and other materials together. Some ingredients are added to stabilize and strengthen the glass like potash, lime, boric acid or caustic soda. Other additives like ground metal oxides are used to color the glass. Some colors of glass like pinks, reds and purples can be expensive because gold is used in the manufacturing process. There are many colors and types of glass available today.

A Fused Glass Chemical Reaction

Preparing the glass in the kiln.

Heidi’s glass piece before firing.

In order to get different colors of glass minerals are added. During the firing process sometimes these minerals create a chemical reaction. My studio partner Heidi decided to experiment with these reactions during her recent studio visit.

Lately I have been creating “hot fire” slabs of glass. The glass is heated to 1700 degrees and held for a couple of hours. At this temperature the glass is more fluid resulting in interesting movement within the piece. After a few disasters, I have stabilized the firing schedule for my kiln. I discovered (by accident) that you get more movement if the kiln is unlevel because gravity is helping the glass move.

Fused Glass

Heidi’s piece after firing.

As Heidi prepared the kiln for her first hot fire piece she worked with copper bearing colors (blues and greens) and sulfur bearing (creams). To make things interesting she threw in some pink/coral which is lead bearing. As you can see from the pictures the chemical reaction formed the dark charcoal brown color. I love the outcome.



Fused Glass Art Fused Glass Art

Heidi will be back in the studio next week. We’ll see what she eventually does with the fused glass. Whatever it is I’m sure it will be fabulous. It never ceases to amaze me how different our approach is to working with glass utilizing the same techniques.