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Complete Beginner, Epic Fail When Firing


WMESArtTeach

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Hey there everyone! I joined this forum in hopes of some help with my ceramics program I run at the school I teach at. For starters I've done a good amount of ceramics in my time, however the studio always had grad students do the loading/firing and us lowly undergrads/paying artists only got to see the before and after. 

 

I now have a lovely Peter Pugger (more on this later) and an Automatic Electric Skutt Kiln.

 

I have fired five times, three cone 04 bisque firings, all of which went perfectly. I watched a lot of videos and read a lot of things. I used a firing schedule I saw used on youtube that fires "low and slow". I like it because with elementary student work, and the amount of pieces going in the slower fire has prevented all explosions so far.

 

I have also fired two unsuccessful glaze firings. The first one 100% my fault, I fired 06 glazes at 04. Only one piece ended up blowing out, and only slightly tipped of its stilts. The pieces however all had lots of what look like popped bubbles on the surface. Also very strangely all of the pieces melted onto the stilts and I had to use a screwdriver to pry them off the pieces.

 

My second glaze firing I only loaded a few pieces, mostly my own in case something went wrong again. And oh my did it go wrong. All of the pieces are black piles of bubbled mess. They look like lava rocks. My stilts are completely engulfed in the clay, and almost every piece is stuck to my shelves. 

 

Here's where it gets weird. The school has no record of buying the clay. So I have no idea how old it is or what it is. It's red, but that's all I know. It was all in bags and a garbage can when I took the job. There was one bag of unopened clay still in the original shape it was shipped in. I used this clay for a few projects but ultimately it ended up being pugged with the existing clay. In this second firing everything  melted but one piece, it was perfectly preserved and the glaze didn't look half bad. Because of this I think that the clay has been compromised. It only makes sense that the one perfect piece was the fresh clay, and everything was the old pugged up clay. 

 

I don't have too much clay left, so its going to be disposed of. I've ordered 200lbs of new clay that I can fire properly. I plan to dispose of my old clay, clean out Peter and move on. But I need to learn from this experience, I need to come out a better art teacher.

 

My biggest question: Can I over-pug my clay? Does repeatedly pugging and adding water change the clay?

 

I've included pictures of before and after, note the one good piece was below the top shelf so you cannot see it. The large blob stuck to the kiln wall was a 7" tall ice cream cone.

 

Any advice is appreciated, especially anything that will save my shelves.

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The clay was over-fired.  Pugging it had nothing to do with the result.

 

Your shelves might be salvaged . . . depends on how deep the clay melted into the shelf.  Wearing appropriate safety gear, remove the items and grind down the shelf -- use an angle grinder if the clay did not melt into the shelf.  If nothing else, remove/grind away all the melted clay and kiln wash to get the shelf completely clean, then flip it over an use the other side instead.  But you won't know until  the charred remains are removed. 

 

Is it possible you programmed the kiln to cone 6 instead of 06?  Did the kiln turn off properly at peak temperature?  How long was the firing? 

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The above post covers it all-except getting rid of all that clay and buying clay you KNOW the temperature that it matures at.

As Bruce said above. Do you know for sure what temp the kiln went to?-also next time put some ceramic cones in fire -those cones need to be the end temp you are firing to-say cone o6 if you plan on firing to cone 06.This way you will know what happened temp wise.

Firing clay you know nothing about is like driving with your windshield painted over-sooner or later it will be bad news.

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You will want to carefully take the bob off the kiln wall-hopefully it did not grab/melt onto that kiln element and ruin it.You should carefully grind it way from that part-it will pull some soft brick off wall if you are aggressive with it-I suggest crunching it with pliers (like channel locks) to make the piece smaller near element.Go slow here-if it melted into element you will have to separate it and get rid of all of it-vacumme it all up when done including kiln floor.

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Thank you so much everyone for the replies. It means a lot to me. As stated I'm completely new to firing.

 

I have removed the shelf from the kiln. The element was not damaged but a decent chuck of brick came too. I have read about saving the piece, breaking it up and using it along with kiln cement to fix the area. As for my shelves, because everything was on stilts it looks as though they should be fairly easy to grind off. The pieces seem to be stuck only around the edges. I have seen this done before, and my fiancee is a GC so luckily we have an angle grinder and safety gear! I'm optimistic about this, also there were only 3 of my 8 shelves effected. 

 

The kiln fired 8.51 (so 8 hours, 30ish minutes) but I believe I fired a 6 instead of an 06. I will have to rewatch the Skutt videos and make sure that I am programming properly. I was so worried about this one going wrong too that I missed a single digit and really messed it up, 

 

Thank you again, I'm sure i'll be back with more questions!

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