cracks in glass

[euneenwendt]

I used a clear glass base and put scrap glass on top, then fused it using a full fuse.  I then tack-fused stars to it after the full fuse.  For the last step, I draped this piece over a mold using a drape/slump fuse.  When I took it out of the kiln, it was cracked.  Can you tell me why?  Was it too much kiln time?

[wordana]

You don’t mention your firing schedule or the size and thickness of the finished piece. However, my first guess is the piece was likely too thick for your firing schedule.

Dana w.

[Becki]

 Or what type of glass your using, how close you are to your elements.  You also mention you tack fused pieces.  Did you anneal long enough?

 

 

Becki

 

[Stephen Richard]

I assume you used a pre-programmed schedule.  Now you know why so many people do not like these.  Many setups are not considered by the people who do the programming of schedules for kilns.  Tack fuses require longer and more careful annealing than full fuses.  Slumping of tack fused items needs slower rates of advance.  Draping of tack fused pieces require even more slow-ness.  So it is not the kiln time.  It is more likely inadquate annealing and subsequently too rapid a schedule with not enough annealing time and too quick an annealing cool.

Stephen Richard

blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

[thomas decker]

if you go to the uroboros website you will find several schedules that you can use for annealing.  different thickness and sizes  of glass .   also I think the bullseye website has schedules that you can use too.  it might help you figure out what is going wrong with your schedule.

[Becki]

 Paul also has a tutorial here to help you understand firing schedules with links to the glass sites for more information.

http://www.fusedglass.org/learn/technical_tutorials/glass_firing_schedules

 

 

Becki

 

[blamdimond]

Did you use fusible tested glass? I know it’s a silly question, but,  I have used rack pack(yes, I know), and have  found that especially during a robust slump that glass sometimes has issues, especially if it has any steaky or wispy white.  I will try again, using a slower schedule on the cooling side and let you know.

[Author]

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