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I have tried a couple times to form a vase on a floral former using two separate, unfired square layers of glass, put at 90 degrees to each other. The design is that the inner layer is transparent and the outer layer is opaque. The transparent is a little larger so that it will "peak" out above the opaque layer when the piece is finished. I figured that the firing schedule would be a bit fussy because as the glass falls they touch in some places and fuse together but not in other spots. As they continue to cool it makes sense that there would be stress as the glasses are different. However, I thought with the right schedule this could probably work but while I have been conservative, at least I thought so, the inner, transparent, glass has cracked on both my attempts. Not right away, but within days. If anyone has done this and would be willing to share a schedule I would really appreciate it. After the slump, I did a 30 minute hold at 1000 deg to make sure it was evenly hot and then held at 900 for 90 minutes. Then went very slowly, 100 dph, to 650 deg. Thanks for any advice you can offer!

A 90 minute hold is probably not long enough. Because of the folding over, the piece will be much more than two layers thick in places, and only one layer in others. I would probably hold around 4 hours.

Also, you'd probably have better luck if you pre-fuse the piece, rather than try to do everything in one step.

Brad, do you mean pre-fuse each piece separately? I really want them to be two separate pieces so that they each can "do their own thing" when they fall. 4 hour hold? Will give that a try. Thanks!

Michele-MD wrote:Brad, do you mean pre-fuse each piece separately? I really want them to be two separate pieces so that they each can "do their own thing" when they fall. 4 hour hold? Will give that a try. Thanks!

Well, that's what I meant, but I understand now why you don't want to do that. It's a really complicated firing in terms of hot and cold spots. All I can think of is to hold longer and pray. Maybe someone else will have another suggestion.

The answer is to not have the folds touch.
Single layer glass will possibly have greater success.
The schedule is critical and I have no suggestion other than trial and error and record keeping.
Brian Blanthorn's term 'Evenivity' of heating inside the kiln will yield more consistent results.
My experience is that if you cannot control every variable including the colour patterns in the glass you will not have consistent success even with a perfect firing schedule.

Paul Tarlow (Helios Glass) shows how to do this in one of his excellent e-books. This particular e-book is called Creative Draping. http://fusedglassbooks.com/

Thanks for the responses. I am using single layers, want to keep the weight down. I also thought about trying to keep the two pieces from sticking together, best I could think of was adding a layer of thin fiber paper, though I thought that could be a challenge to remove and sort of still think this might be a question of having the right firing schedule. I also think the very long anneal could maybe help, though at some point the two layers have to cool and since they are not identical I expect they cool at different rates and that seems like a recipe for a stress fracture. Thanks for the tip about Paul's e-book, too. Michele

Michele, how about one sheet most of the way, annealing and cooling, then adding the second sheet and slump again. there might be would be less chance or fewer places for layers to stick to each other.