So the grand adventure of learning how to manage glass in a kiln begins. I've been pre-firing and priming plaster molds and tack fusing multiple layers of glass, and this morning I took a bowl out of the kiln. I had to wait a long time for the kiln to cool, as the large plaster mold means the kiln takes even longer to cool to room temperature. Glass is temperamental and doesn't like thermal shock, so I am learning patience.
I bought a piece of opaque toffee coloured glass at Creative Glass Guild- they are switching to only carrying Spectrum glass so the Bullseye glass is being sold at a discount. I tried to make myself stick to just one of the types of glass as they behave differently in the kiln and cannot be mixed. They have such different characters though that I cannot do that, so my glass filing/labelling has to be well managed.
The toffee coloured glass is an odd colour for me to choose, but I want to be sure I don't just end up with a sea of sea-coloured glass just because I love it. I have a friend Murgatroyd & Bean who always adds a shot of a colour that she wouldn't normally think went with her palette at a late stage in each of her works, and this gives her work an extra bit of zing. Now that I have used most of this piece of glass I suddenly think I should have kept it for beaches in my seascapes.
The base layer of this bowl is clear glass, and I scattered bits of adventurine green stringer and orange frit and small pieces of red and orange glass on top. I tack fused this so that it kept some of the raised texture but was firmly attached. I placed it carefully on to of the mold I wanted to use only to discover that I had measured the bottom of the mold not the top, and the glass was about 5mm too large. If glass overlaps the edges of the mold it can drop down the outside and snag and pull the glass apart and possibly even break the mold. I did wonder whether to see what happens, in the grand spirit of adventure and a desire to make lots of learning opportunities in this early stage…but then I decided to be cautious and placed the glass on the very large platter mold instead.
I have read that one should look in the kiln when slumping to make sure that the work has enough time to reach the shape you want. I am still trusting the pre-programmed firing cycles. I presumed that this would be sufficient for this quite simple bowl. However, the very centre of the base is shiny and slightly raised where it didn't quite reach the mold. Next time I should increase the amount of time the kiln stays at the stage the glass is sinking into the mold. Unfortunately the book I have looked in, which I bought as it had graphs and data rather than just instructions and pretty pictures, doesn't make it obvious if I increase the short time (ten minutes) at the top temperature of 704C, or the long time (1.5 hours) at the next stage at 516C. More research is necessary.
Looking carefully at the bowl, with my learning rather than admiring eye, I also notice some small patches of less shiny glass. There seems to be several of these areas, which look like areas of glue or some other contaminant. Not sure what caused them, as I did use glue to stop the stringers rolling around before the tack fusing stage, but it is special fusing glue that burns off in the firing. I didn't manage to get them to show in the photo, but they do mar the lovely glossy finish.
Today the world is lovely and sparkly, with frost and sub-zero temperatures. My studio, which is the garage, will be too cold to work in, so I'll have to restrain my enthusiasm and have a day without cutting lovely sheets of glass into smaller and smaller bits.
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