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Spinnerkatie

melted cone on unwashed kiln shelf

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I'm a real newbie to kilns.  I always had my pots fired in a studio.  I had the good fortune to be given a Duncan kiln (40 years old or so, I imagine)  It looked to be in such good shape I wasn't sure it had ever been fired.  I read in the manual that it should be pre-fired to 05 before I did a real glaze firing and so I put the kiln shelves into the kiln.  I didn't have kiln wash but I had read you didn't need it for a bisque firing.  I'm in the midst of ordering cone supports, which I was missing, but I thought (stupidly, I know now) that I could fire without the kiln sitter because I had a witness cone which I would watch.   I didn't have an 04 or 06, so I just put the one cone in and set the kiln to low, fired for an hour, medium for two hours and then switched to high and checked after 2 hours and the cone was a melted blob on the shelf.  So the good news is I think the kiln works just fine.  The bad news is that I have this blob on the shelf.  Can I just grind it off?  It seems like this is the way to do it and then I can just flip the shelf over and it won't matter so much that I have a less than perfect shelf surface?  Am I right in thinking this?  I know the kiln sitter will keep this from happening again, plus I plan to kiln wash the shelves.  But if I did have an 06 in there as a guardian cone or whatever, wouldn't that have melted to a blob before the 05 went over or did my kiln go a lot higher than 05 or even 04 to melt it into a blob.  I'm glad I didn't have any ware in there and I'm hoping I didn't do too much damage to the shelf.

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If the cone melted into a blob, then it went a lot hotter than that cone, like at least 2-3 cones hotter. You can grind the blob level, and either flip the shelf or put a little extra kiln wash there for a couple of firings, then grind it again after the wash has soaked in to whatever's left of the blob and sealed it up. In the future, use the sitter and timer, and always check to make sure it shut off when you expect it to.

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The problem with grinding glaze drips etc off standard alumina shelves is that the shelf is so much softer than the drip.  Using a standard body grinder with an abrasive head is tough because the angle is awkward and the grinding wheel doesn't really cut all that well, so it takes some pressure and multiple passes.  I got some quality diamond dremel bits from lapidary supply recently.  They aren't all that cheap, but my understanding is that the diamond grit isn't just a surface layer, so it will retain it's cutting ability as it wears.  This stuff goes through glaze drips right now.  Pretty easy to grind only the drip and not leave extra holes in the shelf.  Mostly use it for cleaning up drips on feet, but I just redid my bottom heavy shelves.  Very nice. 

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I always try to chip it off in one go before grinding, actually, I never use a grinder, it down to a thin unchippoffable layer of further heat from the grinder meted in blob.

23 hours ago, Spinnerkatie said:

I know the kiln sitter will keep this from happening again,

No. You are the only true line of defense! It will serve you well to not believe that quoted statement anymore!

It also won't keep things from being under fired.

Get them UV glasses and make sure you know how to reset the sitter in case your witness cones didn't fall yet.

You can figure out a way to precariously perch a wine glass in front of the sitter, so when it falls, you hear the glass smash and can go watch your cones. There are safer methods, but who doesn't like to hear glass break?

 

Sorce

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On 7/31/2020 at 8:53 AM, Spinnerkatie said:

did my kiln go a lot higher than 05 or even 04 to melt it into a blob. 

Just a little fun fact: cones are made of glaze just about four cones higher. In other words if you grind up a cone 6  cone and fire it to cone 10  it comes out just like a  melted glaze because it is.  Likely you ended up three to four cones higher. Oh and as a general guide bisque  schedules usually run 10-12 hours (typical) to provide enough time for complete burnout.

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Another thing to remember about cones, the temp of a full cone is different from a small cone is different from a pyrometric bar. So when ordering look at the cone temperature charts to match up your needs.

Another thing to remember about the kiln setter. . . it is mechanical, and requires the use of gravity. If your setter is set right one day, and all is working, no problem and usually not for the life of the kiln if the setter is well maintained. However, as example, I had a setter in one kiln that was attached over two kiln sections. After replacing some elements one day, that required removing outer boxes, leaning inside the kiln to remove/replace elements, and completing the installation. . . I must have moved something in the kiln sections. Next firing over fired as the setter could not drop the control bar as it was leaning against the setter wall. I had botten the section on the top where the setter was connected inward by @1/4" out of alignment with the section below. This was just enough to mess up the firing. Luckily, I had good understanding of how long a firing would take, and had set the setter to within 30 minutes of where I believed the setter would shut down. Very important to pay attention, keep notes on how long a firing takes so that you can set the timer to help out in such instances.

Last piece of advice here is to get a heat color/temp/cone chart to allow you to estimate the temperatures going on in your kiln. These are a good estimate, not intended to replace the witness cones, or the setter, but to improve your understanding of the firing process. I fire my entire load using one of these, waiting until my witness ^5 goes down, watching when my ^6 goes to 90 degrees  to shut off.

 

best,

Pres

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fwiw

  Discovered masonry specific grinding wheel when smoothing and polishing tile edges for a home improvement project - strips away commercial traffic rated porcelain like butter, where a grinding wheel for steel skates over. About three bucks - haven't needed it for kiln shelf clean up (yet) - the local JC Ceramic Techs were using them 'bout every week afore all this/that happened...

  Like candles (of same wax), big ones slump before small ones; some small/large Orton cones are made of same material, some aren't. I buy small cones only, on account of a) slightly cheaper, b) easier to see through the lil' peep c) same cone for sitter and cone pack d) LA does same.

From https://community.ceramicartsdaily.org/topic/21668-kiln-sitter-cone-for-witness-cone

The small cone description has been changed on Orton's website, now reads (emphasis added) "Small Cones used on the kiln shelf deform at about 9°F after Large or Self-Supporting Cones of the same number."

As for formulation differences between Large, Self-Supporting, and Small cones (of same type and number), per Orton Engineer, large cones made without coloration are like small cone formulation, cone 4 through 8 (large cone boxes labeled with "b" after the cone number are made with same formula as small cones). Small cones are "original" Orton formula; some of the Self-Supporting cones were re-formulated - the new formula didn't work well for small cones used in a sitter.

  Cones tell the story - the conclusion of the story - I also rely on pyrometer feedback and firing notes.

2089783582_masonryMa.JPG.402805f1cc195bbd2125bbb49295ca45.JPG

Edited by Hulk
oops

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On 8/1/2020 at 8:37 AM, Sorcery said:

You can figure out a way to precariously perch a wine glass in front of the sitter, so when it falls, you hear the glass smash and can go watch your cones. There are safer methods, but who doesn't like to hear glass break?

Lol. I set this up to fill a Togo bottle and was going to do something else while it filled....

Then I quickly realized I essentially setup this scenario, where the weight of the water would transfer and end up knocking this glass to the floor! 

But who doesn't like to hear glass break! Lol!

Sorce

20200802_084126.jpg

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