I have been working on building the glass program in my art classes. We have had great success in our fusing class at the high school from both the help I have found on the forum and from our local glass center. Lately though I have run into an issue and I am hoping to get some more help.
The issue I have had glass fused projects cracking. I will put the details below and insert a photo as well.
1) A description of the problem.
Glass cracking after it has been fired a second time.
2) If possible, a digital image of the piece is and kiln is often helpful.
I will insert one below.
I get a server error when I try to attach the photo
3) Style codes (i.e. 1101-30), production dates, and sheet numbers for all of the glasses in the project in question.
Tekta Clear glass 001100 0380 possible dates 7/9/14 or 6/18/14 (I have a large bin of clear scraps that we use so not all of them have the date stickers attached.)
ruby pink tint 001831-0030 3mm
powder blue 000108-0030 3mm
Stringers Clear dichroic
On the wreath
spring green 0014426-0030 3mm
Averntine green stringers
Tomato Red Opal Frit Course 00024-0003-F-P001
4) Design of the piece (dimensions, arrangement)
Square: 7 1/2 inches with clear base and glass tack fused on top to create the design
Wreath: Approximately 4 1/2 inches diameter clear base with Cut green pieces on top layered to create the wreath.
Kiln and firing info:
Both Pieces were tack fused once without issue.
Both students added some final touches (stringers onto the square, red round fit onto the wreath) then tack fired again. The cracks and/or separating did not happen until it was tack fused the second time.
Here is the tack fuse schedule.
ramp 1 300 to 1250 hold 30 minutes
ramp 2 400 to 1350 hold 10 minutes
ramp 3 960 to 960 hold 1 hour
ramp 4 100 to 700 hold no
1) Description of the kiln (type, interior dimensions, controller, etc.). Describe location of elements.
paragon kiln square interior shelf 14 inches by 14 inches. Computer controller with elements only on the walls not the ceiling.
2) Firing cycle for this project (including the annealing portion of the cycle)
Kiln Furniture and supplies
1) What kind of kiln shelf are you using? mulliete
2) What are you using for a shelf or mold separator? (Thinfire, fiber paper, shelf primer, etc.)
Bullseye kiln wash
3) Where is it situated in the kiln during firings?
Center of the shelf in center of the kiln
4) Describe any additional kiln furniture used (dams, molds) and the separators used.
no other kiln furniture used
Optional (but encouraged):
Do you have a hunch about what could be done differently to avoid the problem? The only think I can think of is that it looks like a crack from glass that would not be compatible. I don't see how that could be the case because we use only Bullseye fusable glass. The clear is all that the two pieces have in common in terms of materials.
Otherwise it would have to be something with the kiln/firing. This is the same schedule I have been using so I am stumped. I have fired pieces more than once numerous times and have never had this happen.
We could be causing this so I can avoid it in the future.
Could either of these pieces be salvaged/ fixed? If so I'll take any suggestions