Why use glass in ceramics?
Glass and ceramics go hand in hand together (after all normal glazes usually include silica, which is the main former of glass) and putting glass beads in your pottery can create the most amazing results. After your piece has been glazed the light will bounce off the glass making it look quite a lot like a precious jewel. The colors, so bold and vibrant, really catch the eye.
Any ceramic work you produce with glass is guaranteed to be a bit of a showstopper. If you’ve ever heard the term ‘warm glass’ this is the method they are talking about.
How does it work?
The great thing about creating this kind of work is that you don’t need anything special to create it; you can use relatively cheap glass and put it through your normal ceramics kiln, as you can vary the temperature of your ceramics kiln. The main difference between a glass kiln and a ceramics kiln is that glass kilns fire from the top down (typically to get an even heat on flat glassware) and ceramic kilns fire from elements right the way round the kiln to heat the objects evenly. There are some factors you should be aware of however, especially the fact that when glass is heated it expands and when it cools it contracts, so you’ll need to make sure it has the space to do this within your work to avoid the chance of it cracking at any point during the firing.
If you’re starting out using ceramics and glass together, it’s best to start with something simple, like a bowl, that has a fairly wide base for the glass to melt and pool into. Be careful not to use too much glass in your work. Here a little goes a long way and you don’t want to run the risk of the changing state of the glass to crack your ceramics.
What are the results?
There are several different ways you can apply the glass to your work. Firstly, you can put it on top of glazed work, or for a different result you can glaze your work and then scrape back the glaze in certain places and put the glass on these places, there are quite a lot of factors to consider with this as the type of glass you use and the type of clay you use will have a big effect on the finished result. It’s advisable to test out your clays and a little glass together on a few test tiles before you fire your main pieces with glass. However, the results with this type of work are quite literally endless. For a little inspiration, check out the work of the incredible ceramicist Steven Branfman, he rolls his ceramics in crushed glass and puts them through a Raku firing, creating the most mind blowing textures on the outside of his work.
What type of glass can I use?
As with clay, glass changes state at varying different temperatures according to the components it’s made from. Lakeside Pottery writes that ‘standard soda lime silica (the most common kind of natural glass) melts at something on the order of 1500 degrees Celsius (around 2700 degrees Fahrenheit)’ while ‘pure silica needs fluxes to melt at a lower temperature’.
It's best to fire the work slowly to start with. A nice neat way to work with ceramics and glass is to use glass beads as the colors are strong and they are a good size and soft round shape. Avoid the temptation to use broken glass, for two reasons; the temperature it melts at and also for safety.
Are there any issues with using glassware in your ceramics?
The main issue is that your ceramic ware will only be able to used in a decorative sense, the pieces won’t be food safe when fired with glass. The reason for this is that the glass surface will have tiny cracks, which could collect bits of food or dust.