It is a while since I wrote about my first move into glass casting. Having frightened myself working out just how long (for that read expensive) the kiln cycle is for casting glass, I decided to fill the space with a couple of extra castings.
The first is an ammonite. I made one from metal a while ago on the forge and decided that I would like to make a glass one too.
The second casting takes a little more explaining. It is a ‘gold bar’. Using the forge as a heat source to melt lead, I decided it would be fun to cast a mock gold bar using some lead left over from the roof flashings for our extension (that was 10 years ago now). After that I cast one from aluminium too, as I liked the idea of the painted bars looking identical, but providing a surprise when picked up. The glass bar adds another material to the set. I’ll show you all 3 later.
I have used clear glass for the foot and ammonite and a golden tint glass for the gold bar, for obvious reasons. The picture here shows the rough glass ingots in the moulds. To calculate the amount of glass needed you first pour water into the mould, for the foot this was 625ml. then multiply by the specific gravity of glass (2.5), giving 1.5kg of glass.
With the kiln at maximum temperature, the glass should then melt down into the mould, filling it perfectly to the top. The (next) tricky bit comes in calculating the time to anneal the glass after melting. In this case it is 4 days of reducing the heat by 2 degrees an hour. Even then I am told that the stresses can easily cause cracks.
I am a little nervous about this one, partly because of the time it has taken to prepare the moulds, and partly because I have a feeling I know what the electricity bill will be for 5 days of kiln firing. if it works then that is all OK, if it doesn’t…Wish me luck.