glass won't slump/drape after pot melt

[roykirk]

I’m new to glass fusing and slumping, but thus far I’ve been pleased with my results. I’ve experienced a strange problem with my current project, however, and I can’t seem to find any information about what I might be doing wrong.

In short, I took a cobalt blue wine bottle, crushed it, then placed it in a stainless steel pot with a hole drilled in the bottom to run it through a pot melt cycle. The idea was to take the resulting flat melt and use it for slumping or draping in to a bowl shape. The pot melt went flawlessly and the result was an approximately 7” diameter disc of approximately 6 mm in thickness. For the next step I elected to drape it over an overturned stainless steel bowl. I ran it through a slumping/draping schedule that included a maximum temperature of 1200F for 20 minutes. At the end of the schedule, the glass hadn’t budged a bit. Figuring I wasn’t using an appropriate firing schedule, I ran another one up to 1350F for 60 minutes. Again, not a bit of change. Determined not to be defeated, I decided to run my initial pot melt program again (figuring I could start manually ramping it down once I noticed it start to slump). I checked after 60 minutes at 1700F and was astonished to find that once again the glass hadn’t moved. I manually ramped it up to 1800F and held for another 60 minutes and think I noticed the tiniest of droop around the edges of the disc, but after such a long period of time I started to worry about damaging my kiln so I shut it down and gave up.

I’m using a new Kingpin 88 kiln and it’s worked flawlessly outside of the present project. I’m not certain if the result of my pot melt is simply too thick to drape or slump or if the pot melt process changed something about the glass properties that’s rendered it unsuitable for slumping. In any case, I’ve looked all over and I can’t seem to find others who have experienced this problem. Any ideas from the group?

[Brad Walker]

Bottle glass is stiff glass and not always predictable. It's not uncommon for the characteristics to change after a fuse firing. Moreover, a thick small piece such as the one you made takes a lot of heat to drape around objects.

[Judd]

Yeah, cool idea but you're using crap-glass. Try the concept with a tested compatible glass.

[roykirk]

Thanks for the tips. I'll retry the project with some proper glass and see if I come out better.

[Bert Weiss]

Bottle glass is formulated so it can be machine blown in to a hot iron mold, and then stiffen up as fast as possible, so it won't deform. This is not an ideal quality for those who wish to reform the glass.