Expert: Sam Kelly - 2/28/2009

Question
QUESTION: I have a paragon caldera. I do some firing of glass and PMC. I bought some bisque from a local shop and glazed it with hi-fire glaze 4/6. They are 2 coffee cups.
I can set my kiln to fire auto at cone 6, but am a little weary. What speed should I use? If the glaze is 4/6....should I fire at cone 4, 5 or 6...it's a bit confusing.
Second..I have do have kiln wash...but also have shelf paper from firing glass...can I use that instead of the kiln wash..?
So many questions....I appreciate any help.
I am weary...because I have tried firing ceramic beads before, cone 6 and didn't get good results, the glaze ran on me...I realize these pieces are larger, so I don't know what to expect.
Thank you..!

ANSWER: Hi Dawn, If the glaze ran then it was to hot, you are going to have to test at 4 first and see the results, then 5 if the glaze has not matured.

Best not to use the paper. Go to your supplier and buy a piece of leanthal wire(What kiln elements are made from)or a similar product. thread your beads on this carefully and support each end on kiln props.

Watch these videos,

http://www.youtube.com/watch?v=-Ouhjf11pEI

Sam

---------- FOLLOW-UP ----------

QUESTION: Thank you for video link...!
OK..so I fired at cone 4, ramped med and held for 15 mins. The 1 taller mug (4 inches) came out great, including the glazes...the 2 inch cup changed shape...started elongating.
The kiln is 8x8 and I kept the cups from touching each other and the walls..but there wasn't much room.

So...what happened..? Did I hold it too long..?
Thanks again for the help..!

ANSWER: I am assuming same clay, same glaze, approx same thickness. was the pyrometric cone 4 melted flat or in a nice downward curved arc?

Read This:  http://www.walkerceramics.com.au/cones.htm

Fire again using new unused clay the same as used with 4 inch mug.

Sam

---------- FOLLOW-UP ----------

QUESTION: Hi Sam...! Thanks for quick response. Of course I didn't use cones...lol. These were commercially bisque fired pieces that I purchased already fired. I would have to "assume" they are same clay, they came from the same place. They were both placed about the same distance away from the sides of my oh so small kiln. I did use the same glazes on both pieces..and the glaze came out perfectly...at which I was surprised..lol...that was my biggest worry. I just don't know why it was starting to collapse. They are approximately the same thickness...
Sorry for being such a bother, I appreciate your patience with me. This kind of firing isn't really my main focus..I just picked these pieces up on a whim.
Thanks again for any insight on the collapse you can give me.

Answer
Dawn if the pot started to warp and go out of shape that means the clay has gone past it's maturing point, in other words if you were to increase the temp it would melt.

Put some cones in the kiln and see if your controller temp matches the cones, the cones are never wrong, when I fire final temp means nothing, its the cones that tell me when the heat work is done

Sam