1) A description of the problem. The irid glass on the bottom of the project stuck to the shelf causing the glass to shatter.... sharp edges.
2) If possible, a digital image of the piece is and kiln is often helpful. Here is a photo of the biggest piece. The rest is is varying sizes.... shattered. The broken edges are VERY sharp.
3) Style codes (i.e. 1101-30), production dates, and sheet numbers for all of the glasses in the project in question. Sorry. I can't do production numbers and sheet numbers. All glass, except the irid, is from scrap sheets that I have had for a while. With the irid, I used most of the sheet and the label is gone..however it must have been a fairly recent run, since I just got it from Ed Hoy. The color/style numbers are: 0011010-0003, 001101-0031, 000120-0030 and 000220-0030.
4) Design of the piece (dimensions, arrangement) 10" square. Bottom layer: transparent Rainbow irid (irid side down), Clear frit Coarse, Marigold yellow, Orange on top. Three full 10" layers. Sides: bordered by Transparent Rainbow Iris (irid side out).
Kiln and firing info:
1) Description of the kiln (type, interior dimensions, controller, etc.). Describe location of elements. Paragon 24 Professional Series.... like the ones you sell in your show room. Elements on side and top. Sentry 2.0 Controller. Interior dimensions.... probably 22" since my 20" shelf just fits.
2) Firing cycle for this project (including the annealing portion of the cycle)
Fired twice: First time:
400F 1100 :30
600F 1700 1:30
AFAP 1500 :10
AFAP 900 2:00
100F 800 :00
180F 700 :00
AFAP 70 :00 (My kiln won't do the 600 degrees your schedule calls for, so I tried this.)
Result..... major shattering. Sharp edges. So I decided to just program the kiln to shut off at 700 and cool naturally and ran the same schedule again. I did not touch the piece in the kiln before restarting it.
Second time.... as above with the modification of shutting the kiln down at 700.
Result....some cracks healed. More appeared. Stuck to glass only on right side....along the edge from center to the front.
Kiln Furniture and supplies
1) What kind of kiln shelf are you using? Cordierite 20 x 20 x 3/4"
2) What are you using for a shelf or mold separator? (Thinfire, fiber paper, shelf primer, etc.)
Shelf primer, Primo Premier. Fiber paper along sides.
3) Where is it situated in the kiln during firings? On 1" kiln posts that rest on the floor. The piece was centered on the shelf.
4) Describe any additional kiln furniture used (dams, molds) and the separators used. I use Bullseye dams along with 1/8" thick fiber paper cut into strips for the edges.
Optional (but encouraged):
Do you have a hunch about what could be done differently to avoid the problem?
I suspect that I accidentally got the irid glass wrong side down.... but then it should have stuck everywhere.... and it didn't. My question to you is............ is there anything else that could have caused this?