If you were wondering just how some of the kiln worked glass on my site is created, this blog post is the first in a series on how some of the processes are done.
When you kiln work glass, the most important piece of equipment is - you guessed it - a kiln. Most kilns today are electric but there are some that are gas or even wood fired. A kiln is a box made of fireproof bricks that can heat glass to extreme temperatures safely. Glass is heated as high a 1500+ degrees Fahrenheit, depending on the desired result. Heat control is the very essence of the design of your final piece. A ‘full fuse’ is the melting and flowing together of several pieces of glass, this is usually the highest temperature for most projects. A ‘fire polish’ is at a lower temperature than full fuse so that the edges will round and become shiny but the shape of the object does not change. The temperature used depends on the desired result.
One concern I will address here is bubbles. You may have browsed some glass art and noticed some tiny bubbles in the piece. Bubbles of this nature are normal and are called champagne bubbles. These bubbles are essentially air trapped between the glass.
You can never really eliminate bubbles but they can be controlled to a degree. Sometimes bubbles can actually be created for a desired look.
1Bubbles used as a design element.
Other times bubbles present large problems.
1 Photo from Spectrum Glass Company
Layering glass without any way for the bulk of the air to escape is how disaster strikes and ruins an art piece. Glass must be layered in such a way so that air can find a way out during what is called a ‘bubble squeeze’.
Maybe I need to backtrack a little. Kilns heat glass with what’s called a firing schedule. This a sequence of heating events that the kiln follows in heating and melting glass. For instance, a slow ramp up so as to not shock glass when heating, a soak time at the top temperature, a slow ramp down to room temperature to prevent shock here as well (called annealing). A bubble squeeze is a long soak at a temperature certain temperature that allows the glass to soften and melt in a way that gives the air time to squeeze out.
Controlling bubbles is something that is learned through experience and getting to know the idiosyncrasies of your kiln. The best thing is to think ahead when layering glass, decide the best firing schedule for your project, and getting familiar with your kiln to avoid ‘surprises’ when the kiln door is opened to reveal your creation.
Stay tuned for more in the next post!