Glass Bottle Kilns

Chianti kilns by Alberto Cavallini and me

As a rule, we potters have a great rapport with wine. A ritual here in The Chianti region of Italy that accompanies all of our firings.with the accomplishment of every 100 deg.c in the kiln, a toast is made, and as our experimental kilns, are predominantly fired in piazza’s , a fine gathering of friends and on lookers, are always on hand to Brindisi.

Our experimentation with open air kilns began almost ten years ago, using where ever possible old pallet wood, or furniture factory waste for fuel. And several of our kilns themselves built from Thrown away material.
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The idea of building a Glass Bottle kiln began in 2006 during a trip to French potters town of Laborne. We had been invited to participate in a wood firing festival, where each of the village kilns, were fired by an international guest potter. During one long evening firing, we heard someone talking about the possibility of a glass kiln. On our return to Italy Often, we would speak about this idea. finally one morning we decided to experiment the idea.

Our first kiln we used around 150 wine bottles. The principle was simple, as glass shares most of its properties with clay, and if clay is heated too fast, then it will explode, as will a glass bottle if thrown into a bonfire.

We marked out on the ground a circle aprox a meter diameter, and lay each bottle side by side, with necks towards the center. (The thought being, when the necks would become soft from the heat, they would bend down closing the bottle, and creating the closed air space) . In the center we built a small platform, and placed on top some raw pots. On the side from where we would fire, we built a small simple firebox, using an old kiln shelf as a cover ,this is important,as the early flames from the fire must not go into the kiln and touch the glass, untill a good temp. is reached, normally around 400deg. Next was to mix some field clay with builders sand,( the clay is not important even if it has vegetation or stone in ) a ring of clay was placed around each bottle shoulder, , this then holds each bottle in place, and also closes up the air gap between bottles. With each level the ring becomes narrower, and an igloo shape is formed.

On lighting the first kiln, we wore eye protection, with the small chance that a bottle could blow. To our surprise and delight we reached around 600 deg.c with no explosions. But on that first kiln, we realized that we had closed the chimney center hole too much by the bottle necks, and the kiln chocked and blocked early on.

Powered by the relative successful of our trial, mark 2 was built , with a few small changes, we decided on a small fire brick base wall, to help slow the cooling process, and give a firm grounding to the glass dome.( not essential)
In the 2nd trial we used around 500 bottles. When we arrived at a height of aprox. 1.5m with the dome closing towards the center, an idea came to us to reverse the bottles, with necks pointing out, so as not to close the chimney tube. We also added final ring of bottles standing on their base, with labels facing outwards, creating a chimney.

We invited friends, and potters from our association, and made a fine day event. As we approached the hours of darkness the kiln closes to 1000 deg. We were awarded with a magnificent magical show of transparent glowing melting glass.

The following day, with the opening of the bottle kiln, becomes almost as exciting as the firing it’s self. On the outside the bottles were all intact, and on breaking down one side, we were awarded with a gem of a cave of melted bottle necks in the form of stalactites, some stretching twice as long as the bottle its self, and even with traces of paper label on the outside, showing the amazing insulation of an air filled bottle. Our pots were fired, with an added bonus of wonderfully dripped glass icing covering the pieces. Firing your pots in clay saggers, would prevent glass drips.
We have also experimented with the shape and form of the kiln, some have been built as large oval forms, and high bottle shape forms, and we found that it was necessary to support the waist of the kiln, by using sticks of wood and wire, so the belly will not slump out ways. As soon as the clays dries and firms up, this can be removed.
Another option is a small iron grate in the firebox, will allow for much easier temperature control.

We play with different colored glass, transparent white wine, and Chianti classico green, giving colored light effects during the final stages.
The kiln can be re fired, simply by breaking down a small door, to remove and replace the work to be fired, and then built up with new bottles.