Musings about Fusing Glass with the Microwave Kilns


I’ve been teaching the microwave kilns for a few months here. Here’s my latest thoughts –

The new microwaves are nice, but they seem to be more powerful than the last one. I’ve started doing 5 minutes at 50% power, because I was getting cracking glass, regardless of the size of the fused piece.

So, while in general the bigger the piece, the more time it needs for a fuse, that extra time seems to be pretty small.

5 min 50%, and 6 minutes full power – fully fused, and tending every so slighter toward blob.
At 5 min 50% and 4 minutes full – not beginning to fuse. Plus 1m30s fully fused.
5 min 50% and 4 m 30 sec full – red hot but edges still looked sharp. Added 30 sec – not fully fused, but no sharp edges.

Still had one of the bigger, piled high pieces crack even with the 5 m at 50%. Might go to 6 m 50% for large and multi-layered pieces.


Are you firing more than 1 piece in a kiln? We have a total of 6 kilns now. I would do 1 item per kiln to get even heat distribution.


Yep. Only one piece per kiln. The new microwaves require that slower start-up time.


I’ve used them several times with no issue? I’ll check with Jim H he had been using them a lot. The only thing he mentioned is they are building up dust and it’s pitting the glass. The need a wipe out before starting. A mask is always needed when messing with the dust.

FYI, Please do not use water on these! They absorb like a very dense spong and hold water for weeks.


Maybe my folks are making bigger pieces? I am having serious cracking issues if I don’t start with the 50% power option, and I didn’t have that issue in your microwave.


Also, are you using 90 or 96? 90 may act differently.


I did a test run since I have a class this weekend.

3 layers of your class glass. A large piece run on high 9 minutes. Full fuse 9 minutes

I also taped you box closed and wrote class use only. Hopefully people will respect that and not use your clas



Huh. No idea. Nina’s piece was about 4 layers of little bits… You must have the “touch”.

Probably good. I haven’t noticed any problems with a shortage of glass…


Fired a few pieces.

5 min 50% power

4 min is definitely not enough to get the kiln up to temp. Even the tiny piece wasn’t glowing.

Used 5 min 30 seconds on a bigger piece – one edge still looked sharp, so kicked it for 2 30 sec runs. Oh, and this one nearly cracked in the cool-down. It had a crack, but it wasn’t across the piece.

2nd big-ish piece – 6 mins. Full fuse, not too over-melted. Still sort of rectangular. All design pieces melted down into the base.