Boiling Glass

Boiling glass or boiled glass is a high fire process that is accomplished inside a kiln.

Reading the TechNotes from Bullseye will help you understand what transpires as you bring glass to a high temperature inside the kiln.

Although glass doesn’t boil in the sense that water boils, if heated to a high enough temperature, some glass will lose elements of its make-up and start to vaporize.

This old Klaus Moje technique creates what is similar to the appearance of boiling glass.

As the various layers move up towards the top layer, they form bubbles bring up the different colors.

These bubbles pop and spread out over the surface.

About the best information on the internet regarding this procedure is the TechNotes #4 by Bullseye.

If you look at the notes on “Heat and Glass” you will notice that they show a chart that indicates what happens as glass gets hotter inside the kiln.

At between 1600-1700 degrees Fahrenheit bubbles begin to appear from the bottom layer and up through the top surface.

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As the glass gets hotter, trapped air bubbles start to rise to the surface.

This is caused by the high temperature inside the kiln and the chemical changes in the glass as it begins to get more fluid.

As the bubbles begin moving towards the surface they drag the color up through the various layers.

So, although the glass actually doesn’t boil, the popping bubbles give the glass an appearance of boiling.

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Boiling glass can be fantastically unpredictable.

Some will tell you that glass won’t boil, but try this technique and you will become a believer.

Through the use of high heat the bottom colors bubble up to the top leaving.

In this process, they leave their own unrestrained signature and make unique designs in the glass.

Glass can shift out of COE when taken to a higher than recommended temperature.

Since the elements of the original formula are vaporizing this could change the chemical make-up of the glass.

It stands to reason that the gases in various colors would be different.

Keep detailed notes of what transpired during your firing so that any successful outcomes can be repeated and any mistakes can be avoided in future firings.

There are three ways you can attempt to get bubbles:

1. Heat the glass until it reaches 1600-1700 degrees Fahrenheit.

2. Add bubble powder or baking soda to the lowest piece of glass in the stack.

3. Stack the glass so that air is trapped in the lowest level.

Here are the steps to heating the glass to achieve this appearance:

  • The kiln shelf needs to be coated with about 12-14 coats of a high fire kiln wash.
  • Layer glass at least 3 layers thick so that color will be pulled to the top.
  • Place glass on some fiber board
  • Use a dam or some object to keep the glass from running off the shelf.
  • Bring glass up to about 1600-1700 Fahrenheit depending on your individual kiln.
  • Wear protective lenses to view glass to see if it has indeed boiled.
  • Bring glass down to about 1500 degrees Fahrenheit to stabilize glass and smooth out the surface.
  • Anneal and bring the piece to room temperature.
  • Inspect the fired piece for any stress cracks after firing.
  • There are chemicals that can be added to glass that will produce gases during the firing process.

    These can also give a bubbly look to glass.

    Another alternative would be to layer the glass in a manner that would trap air.

    When fired any trapped air would come to the surface.

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