You’ve probably been told that you should never ever put any metal into your microwave and have consequently questioned whether or not it would be sensible to fuse metals to glass in a microwave kiln. Today’s posting is just a short note about this very issue.
I was getting confused by conflicting information so I thought I’d do some reading and experimenting. I have recollections of a gold-rimmed plate producing sparks conflicting with an observation that metals are used in the inside of a microwave oven and clear evidence that precious metal clays (eg silver) are used in microwave kilns. And then there’s the metal in the packaging of microwave popcorn.
To learn about the physics relating to metals in a microwave oven I began my search at http://en.wikipedia.org/wiki/Microwave_oven#Metal_objects and trawled the Internet for further reliable information. Information is power. My understanding is that long thin pieces of metal form an aerial that produces high voltages that turn nearby air into a plasma which allows electrical current to flow to earth – it all sounds reminiscent of electrostatic discharges in physics lessons at school. The answer seems to be that you should avoid using long pieces of metal wire that look like an aerial (which turns out precisely how microwave popcorn packets do their magic).
The first experiment was to remove the glue from the back of some copper foil, clean it, then fuse it between two pieces of fusing glass, clear on one side so that I could see what was happening inside the fused area. You can see that the presence of air and extreme heat within a microwave kiln causes the copper to oxidise – but not consistently so you get some nice variety in the colours.
My next experiment was to fuse six kinds of metal wire that I could find into scraps of fusing glass with a clear cap so that I could see into the fused area. I used different colours of backing glass so that I could remember which piece used which type of metal.
The kinds of wire I tried were brass (intended for picture hanging), copper, tinned copper, zinc-plated iron as well as some high temperature wire purchased from my glass supplier.
I tried a variety of ways to form the loops, as you can see in the picture, from a simple overlap to U-shape or twisted loops. Getting the glass and metal assemblies to sit still is a bit of bother so more experimentation is needed. The U-shaped loop caused the least trouble. The twisted wires cause the most trouble. Perhaps a drop of Glastac is all that’s needed?
All the metals fused into the glass successfully. What differs between them is how the metals reacted to the heat and the presence of oxygen in the atmosphere that causes oxidation. Some metal wires, such as the brass wire and zinc-plated iron wire, discoloured and produced powdery residues that needed cleaning away. Others, like the copper wire, turned black through oxidation but produced no messy residues.
I found that each kind of wire could be cleaned up, but not well enough in some cases. The brass wire was the least satisfactory in my opinion as it remained badly discoloured. I think it’s best to assume you’ll need to apply some copper-coloured or black patination to get a good finish to the loops. I’m sure I’ll find a use for fused metal loops someday but until then I will continue to use glue-on bails.
So, the answer is that you can put metal into your microwave kiln without causing a major catastrophe but you need to do some experimenting to check the quality of the results before embarking on a major project.
Soon I’ll let you know how my experiments with decorative paper hole punches turn out. If the makers of greetings cards can punch out fancy shapes from cardboard then surely I can do the same with thin copper foil.