What went wrong?
Posted: Mon Sep 29, 2003 10:42 am
Hi, I taught a class this weekend and I have no clue as to what went wrong. I have been making dichroic glass jewelry for over 6 years (I have 80 + wholesale accounts) and have never had this happen before. I have also taught this class, using this kiln, about 3 times and using a different kiln twice.
All the glass I was using was Bullseye or Uro 90 (some of my dichro is coated on Uro). We used a coe 90 black irid, a clear, some cobalt blue as our bases and the clear caps. We were using dichroic pieces that have been fired before with a clear cap (by me so I know the glass was all COE90) and unfired dichro (again all was from my own supply so I know it was COE 90). Some of the dichro was Austin Thin but the majority was CBS. Every piece has been used by be in my jewelry. It has never cracked or divitried.
I fire using this schedule, in my kiln, with these glass combinations at least once a week and never a problem!
First the results:
About half of approximately 60 pieces, randomly positioned in the kiln were very cracked and divitrified. They were not pieces made only by one person. They were not grouped together. They were not all the same base glass. They were not all using prefired pieces. They were not all using unfired pieces. They were not all using a combination...... I think you get the picture, there were no common factors. It was so bizarre!
Here is the schedule, it has alway worked before. Keep in mind the largest pieces are not more that 2" by 3". I cut the base glass and the clear glass into 1 1/2" - 2" by 3" strips for each student to use, they can cut those smaller if they want or use them that size. The pieces may have many layers ie. base glass, piled dichro shards, clear cap.
500 degrees per hour to 1000
AFAP to 1400
300 dph to 1500 soak time entered 15
(I shut it off as soon as the majority have been cooked to satisfaction, in this class we try to have them quite well rounded because a lot of the students don't have kilns and want nice rounded cabs at the end)
Since I am teaching and the majority of the students don't have fusing experience we do look into the kiln at various temperatures. I do this every time I teach and so it is not something new. (learned it from Bob Leatherbarrow so how could it be wrong!) I crack the kiln about an inch for about 20 - 30 seconds. We look in at about 1100 to see if it is starting to slump, again at about 1300 - 1350 to see the edges getting shiny and again after a few minutes of the soak at 1500. I then shut the kiln off and go home, nobody touches in until the next morning, no opening and thermal shocking. The only shocking was mine when we opened it Sunday morning!
Does anyone have any word of wisdom for me, I hate teaching when you have to say "I absolutley have no clue what happened!" Makes you humble!
Katy
All the glass I was using was Bullseye or Uro 90 (some of my dichro is coated on Uro). We used a coe 90 black irid, a clear, some cobalt blue as our bases and the clear caps. We were using dichroic pieces that have been fired before with a clear cap (by me so I know the glass was all COE90) and unfired dichro (again all was from my own supply so I know it was COE 90). Some of the dichro was Austin Thin but the majority was CBS. Every piece has been used by be in my jewelry. It has never cracked or divitried.
I fire using this schedule, in my kiln, with these glass combinations at least once a week and never a problem!
First the results:
About half of approximately 60 pieces, randomly positioned in the kiln were very cracked and divitrified. They were not pieces made only by one person. They were not grouped together. They were not all the same base glass. They were not all using prefired pieces. They were not all using unfired pieces. They were not all using a combination...... I think you get the picture, there were no common factors. It was so bizarre!
Here is the schedule, it has alway worked before. Keep in mind the largest pieces are not more that 2" by 3". I cut the base glass and the clear glass into 1 1/2" - 2" by 3" strips for each student to use, they can cut those smaller if they want or use them that size. The pieces may have many layers ie. base glass, piled dichro shards, clear cap.
500 degrees per hour to 1000
AFAP to 1400
300 dph to 1500 soak time entered 15
(I shut it off as soon as the majority have been cooked to satisfaction, in this class we try to have them quite well rounded because a lot of the students don't have kilns and want nice rounded cabs at the end)
Since I am teaching and the majority of the students don't have fusing experience we do look into the kiln at various temperatures. I do this every time I teach and so it is not something new. (learned it from Bob Leatherbarrow so how could it be wrong!) I crack the kiln about an inch for about 20 - 30 seconds. We look in at about 1100 to see if it is starting to slump, again at about 1300 - 1350 to see the edges getting shiny and again after a few minutes of the soak at 1500. I then shut the kiln off and go home, nobody touches in until the next morning, no opening and thermal shocking. The only shocking was mine when we opened it Sunday morning!
Does anyone have any word of wisdom for me, I hate teaching when you have to say "I absolutley have no clue what happened!" Makes you humble!
Katy