Dear Captured: I have a solution for you but I would like a little more information about your project before I make my pronouncement. Stuff like, the diameter of the flat blank, the base glass color and type, how many base layers, what type of decoration, did you add a perimeter border, what was your target intention temperature and hold time for the drape schedule? Also if you can email a photo of the bowl as it is now that would be a big help.
Reply from Captured: OK here a couple of photos of the bowl stuck on the mold. In one of them I'm pointing at an area where the glass has pinched in around the mold. Here is what I did: I cut a 12 1/2" (32 cm) diameter disk from System 96 clear and only used 1 layer because I wanted to keep the bowl as light as possible. Then I added a 4 1/2" (11.5 cm) black glass disk to the center and decorated the rest of the disk from the center out with various colors and grit sizes of frit and some stringers. I did not put a border or decoration around the perimeter so the edge is only a single layer of glass. I modified the drape schedule that came with the mold by adding 20°F (11°C) to the target intention temperature to make it 1250°F (677°C) for 10 minute hold because that is what I have used successfully for slump firings in the past. So what's your solution? I can hardly wait!
Dear Captured: To avoid this predicament in the future let's look a few things that I suspect may have caused it in the first place.
1. A diameter of 12 1/2" (32 cm) for the base disk is too large for this mold. We do not recommend anything larger than 12" (30.5 cm) diameter - so that's important.
2. Even with a 12" (30.5 cm) diameter disk, a capture like this can still happen particularly with a single layer blank that does not have a rim border (that would give the border a little more substance and rigidity).
3. If the target intention temperature of the drape is too hot the glass will over-soften allowing the edge to curl under the lip of the mold. Even though you used a target intention temperature that worked well for slump firing in the past, I suspect it was too hot for this drape particularly with a single layer edge. You might need to drop your target temperature back 15° to 20° to compensate.
OK you've waited long enough - here's the fix. You can save the bowl and the mold by firing it again. You said you added a foot to the bottom so leave the fiber rings in place and put the bowl (with mold inside of course) back into the kiln standing right side up on the foot. Note: If you did not add a foot you would put it into the kiln standing on the bowl base. Now set your kiln controller to use the standard drape schedule but reduce the target intention temperature to 1000°F (538°C), set a 30 minute soak then set your controller alarm to go off at 1000°F (538°C). If you don't know how to set the alarm on your kiln controller, you'll have to read the owners manual again (you have read it at least once, right?). Now when the alarm goes off, put on your kiln gloves and safety glasses, open the lid and take a look at the bowl rim. It probably will not have moved away from the mold just yet - but it will soon, so close the lid and be patient (and don't leave the kiln room). Allow 10 minutes soak and look again. If the glass has moved a little (but not enough) simply close the lid and let it soak a little longer. If the glass hasn't moved at all you can try adding 10° to 20° to the target temp (again, this is in the controller manual so read and figure out how to do it ahead of time). Then wait until the new temperature is reached and take another look. This is very much a wait and watch process that you cannot hurry because if the glass gets even a little too hot it will collapse and fall down around the mold - so low and slow is the only way to go. By the way, even if this recovery effort works perfectly the bowl will have some rim marks from the mold and possibly other edge blemishes, but the bowl and the mold will be saved and you will have learned a lot about your kiln and how glass reacts at lower temperatures. Good Luck and be sure to send me pictures.
Reply from Captured: I did it and it worked - attached are some photos of the bowl in the kiln before and after firing and one of the finished bowl. You're right there are some marks and odd angles around the rim but that just adds to the mystery of my piece that I call "Houston - I Found a Black Hole". Just so you know, I had to go to 1020°F (549°F) in my kiln before the glass started to move then it only took a 5 minute soak to back off the mold before I hit the 'Skip Step' on my controller to send it into the 'drop to anneal' segment. Thanks for helping me save this bowl. - Released (and relieved) in Des Moines
Dear Released: You're welcome and I love the bowl, keep up the great work!
- The Fuse Whisperer