Chemistry in the Kiln

Having an undergraduate degree in chemistry, and having spent numerous years involved in research (as an undergraduate student, graduate student and on the UM faculty), I do have a tendency to look at what is actually happening when I am doing various crafts that involve chemicals.

This was the case when I was learning how to dye fabrics and yarns, when making yogurt, and in my cooking and baking.

So, when I saw some fun ideas for creating bubbles in fused glass, I decided to learn a bit more about the idea.

Calcium carbonate is a chemical compound with the formula CaCO3 and a very pale green color. Upon heating, it releases carbon dioxide, a thermal decomposition reaction, to form calcium oxide. CaCO3(s) → CaO(s) + CO2(g)

The temperature at which decomposition occurs is higher than the slumping temperature of glass. So, when calcium carbonate powder is placed between two pieces of glass, the glass slumps and seal the powder in the space between the glass. As the temperature is raised, the decomposition happens and carbon dioxide gas is generated, creating bubbles. But, because the glass is sealed together, these bubbles are trapped between the pieces of glass. And, the resulting calcium oxide is a lovely turquoise color.

I set up to test this idea in my kiln. But, I decided to test some additional powders as well. Cobalt carbonate, copper carbonate, nickel carbonate, sodium bicarbonate and Borax were sifted onto 1″ x 1.25″ pieces of glass, capped with a second piece of glass and fired in the kiln at a full fuse schedule.

All of these powders created bubbles. The carbonates worked really well, giving some lovely blue, turquoise and grey bubbles. Unfortunately the sodium bicarbonate created a really large bubble and will not be very useful for some creative glass ideas. The Borax produced very small bubbles, more experimenting is needed to optimize the use of Borax.

This lead me to some really fun ideas. I think the cobalt carbonate would be nice to use for an underwater scene. I am hoping to give that I try sometime this year.

The copper made me think of winter. And, since I needed a napkin holder for the winter months, I had an idea.

Using some scrap electrical wire, I cut a couple small pieces and spread the individual wires out to look like the trunk and branches of a tree. Copper is a heat stable metal that I have used in other projects. These copper pieces were placed on a piece of clear glass. Then, using a cardstock stencil, I sifted some calcium carbonate over the trees to create the image of the tree. After capping with a piece of clear glass, white opaque frit was sprinkled to create some “snow”.

After fusing, the trees were great, but I decided to tack fuse some more white frit to make more snow.

I was really happy with the resulting glass. After slumping over a mold, the napkin holder (seen above) was ready for use in my kitchen.

I am looking forward to some more “chemistry experiments” with my kiln.

3 thoughts on “Chemistry in the Kiln

  1. Great explanation. On rainy days I did some fun experiences like this with my sons. I like the idea of using kids volcano technology for fabric.

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