Untitled (For Now) – RAW 5/52

Untitled for now – RAW 5/52, originally uploaded by GinkgoGlass1.
This Ring of the week appeared from a kiln disaster. I was really disappointed when I opened the kiln and saw this big bubble in a grid of very carefully placed ones. I have no idea how this happened, but it is a pretty amazing effect. Possibilities include uneven glass trapped some air under the bottom sheet, some glass cleaner was still present and caused steam or the kiln was too hot.
If you have any ideas as to why this happened, please post in the comments; I would love to be able to repeat this.
This one will eventually turn into a mixed media piece.
Here is a closer view: