Sorry about my English - I'm Russin sitting in Israel.
It was my very first "pure art" project, and it cracked!
One layer of gray cathedral Spectrum 96 70x30 cm with mosaic fish under it and clear "waves" above; large pieces of clear and white around (forming the thick layer of the "ice bank"); frits and small pieces of cold clear colours. I fired and annealed according to System96 instructions for
more than 20" and 3/8" thickness, 710C on top.
It has a long crack with the smooth edges going from the thick layer to the center. I tried to repair it by putting on pieces of clear glass and firing once again; it cracked second time near the first crack. Need a photo?
I need an advice of your years of experience!!!!!!!!!!
Anna wrote:Sorry about my English - I'm Russin sitting in Israel.
It was my very first "pure art" project, and it cracked!
One layer of gray cathedral Spectrum 96 70x30 cm with mosaic fish under it and clear "waves" above; large pieces of clear and white around (forming the thick layer of the "ice bank"); frits and small pieces of cold clear colours. I fired and annealed according to System96 instructions for
more than 20" and 3/8" thickness, 710C on top.
It has a long crack with the smooth edges going from the thick layer to the center. I tried to repair it by putting on pieces of clear glass and firing once again; it cracked second time near the first crack. Need a photo?
I need an advice of your years of experience!!!!!!!!!!
Russian in Israel
We very international here but is great
I am not very experianced still learning my self
But
If U got no mould ie undercuts
Then could B the surface undulations need more anealing
Thick thin realy needs more
One common first timer's thing is after aneal cooling 2 quick
Pic would help 4 the experts oppinion
But U will need 2 get used 2 things breaking / going wrong
But thats where the secret stuff is
U just gotta look
Another thing U realy need 2 do compatability test on all glass
Brian is right about cooling big things down more slowly, and taking them out cooler than thin things. With all the right annealing schedules, and perfectly compatible glass, if you cool it too quickly it will crack. Pieces that go from thick to thin are particularly susceptible, due to the inherent unequal heat transfer rates within the piece. Wait to take it out till it is within 20 degrees or less of room temperature.
You said "It has a long crack with the smooth edges going from the thick layer to the center", does that mean your crack has smooth edges on it? Were you doing a tack fuse? I'm taking that the 710C is equalling 1310F. If the edges of the crack are melted over, you might of heated the piece too fast.
If the edges of the crak are smooth, then you cracked while heating up. With all the layers and varying levels of glass you probably need to heat up more slowly than the Spectrum schedule suggests. Another possibility could be incompatibility of some of your glass. Is it all system 96 glass? Any chance you used even a little something that was not system 96?
If you gave us more details about the glass and the schedule we could better help you. Posting a picture would help too.
Barbara
Barbara
Check out the glass manufacturer's recommended firing schedules... LATEST GLASS
if you get a crack in the same place again, my guess is that you have a piece of different COE glass.
I broke six bowls in a row one time before I realized that the scrap glass I was using to slump with from one glassblowing shop was COE90 and the other was COE 96.
