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Seedy Potter

Large Flat Pieces Cracking During Glaze Firing

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I fire these vertically.. Not flat on the shelf. They are flat ,no warping usually. largest dimension has been 25"

 

I found myself saying" put your visor back down Marcia' as you approached the kiln after fire stomping!

Have to be a wet day in Oz before I attempt that!

Exciting!.

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Marcia:

If I ever have to slay a dragon I will be calling: you seem to handle fire nicely!

There are some premises that need to be mentioned. Raku clay is much more tolerant of thermal shock, hence it should be able to handle the differential of shelf temp verses air temp. I have to use porcelain, so I have to work within the limits of that body. Secondly, I fire upwards of 100 pieces in my 16CF, I do not have the luxury of loose packing due to price points. So I have found other solutions, one I posted in the "broken platter" thread. Another was meeting Ron in KC in order to formulate my own porcelain body that can handle thermal shock "better", and increase the COE of the body to 6.35 in lieu of the usual 5.25.

The final was to make my own custom setters that stack easily, circulate heat better, and more importantly cool evenly.

 
I fire in bisque vertically, but I do not have the luxury to glaze fire vertically due to glaze run.

Flat Firing

 
Nerd

 

By the way, I am rather fond of Dragons.{Paragon}

 

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Glaze nerd,

hah! My shelf I posted re. Drilling holes in shelf looks similar to yours. I still have some Pemco frit 283 . If I ever finish everything I am doing, maybe I'll go back to crystalline glaze firing. I haven't done any since 1975. Frit should still be good.

Marcia

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HAH-- back at ya... What is the old saying "great minds think alike."  Pemco 283 is gold dust in the crystalline glaze biz. Cerox 506 has also been phased out. I know several who bought hundreds of pounds when they still could. Give up that nasty ole raku and come back to your roots. If Fred Sweet ever shaves his beard I will use if for wadding- looks like it could handle cone 12.

Nerd

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nerd, Fred thinks you should read the crystalline glaze article in the latest PMI.

I am considering giving it a go. I think I have 20or 30 pounds of that old frit.

I will post some of my old crystalline pots. I have one in the Springfield , Illinois State Museum that was

A deep navy blue with electric blue crystals. I had a tiny vile of uranium nitrate.

marcia

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What type of sand did you use? I was advised to use silica sand but find it hard to find? can any sort be used? I have to fire 11 inch earthenware clay wall pockets. I fired a plaque flat on my kiln shelf recently and it cracked right down the middle. I have a small electric automatic kiln. If I buscuit then glaze fire them standing on their edge will that be better or will they warp?

 

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Hi Moon- welcome to the forum.

some pottery supply houses sell "china sand" which will work. Plain river sand will also work. River sand is also used by brick layers, also used in pool filters.  

If the edge is wide enough to support the weight, then  yes.

the other issue is quartz inversion which occurs at 1064F (563C)  when firing large pieces, heavy pieces, or pieces with a lot of shelf contact: slow the firing down to 100F an hour from 1000 to 1100F. Do a forum search as "quartz inversion", I recall that thread from a few years back.

Tom

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You can also use sticks of clay as rollers.  Make them about as thin as a pinkie finger, or extrude them, lay them out like sun rays, and put your plate on that.  Somewhere here there is a whole thread, with pictures (if my memory .........)

 

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