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Varying The Thickness On Test Tiles To Produce A Slow Cool.


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I just came across this statement. "It is wise to augment your testing with glaze tiles that are much thicker and heavier than the standard flat thin upright ones. A comparison of the glaze on thin and thick tiles will give you a good indication of its reaction to faster and slower cooling cycles (the heavier ones will cool slower and allow you to see any tendency for the glaze to devitrify or crystallize)"

 

Anybody ever tried this before? I have always used thin test tiles. Are we talking an inch thick or so?

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What is the application for this? Is it just to see what glazes will look like if slow cooled without running a slow cool program? I am not sure I am 100% confident this would yield any different results. I have fired some pretty thick stuff from when I was starting and the glazes on the test tiles that I used looked just like the thick vase bottoms that I fired. I guess you would have to make them really thick.

 

If you try it let me know. As of right now I run two firings for each set of new glazes I make. I make a bunch test tiles, then I fire a bunch in a normal program, then another set again in a slow cool program and compare the differences. The ones I like I run in my middle program to get another result, which is a normal firing with a slight slow cool. 

 

If I could skip all this by making some inch thick tiles that would be interesting.

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I think it probably only hints at the difference a slow cool could make, having never tried it I am not sure but I will be trying it out.

 

I have a, what is probably classed as a rutile blue that seems to be very picky. Every firing it changes. Read a little about it really needing a slow cool and having it look the best on my thickest bowl not fired with a slow cool. Sometimes it comes out a dark blue/brown with no variegation. I thought it was a thickness issue but could be cooling. Probably both.

 

Could be good to run test that show if a slow cool could work, but then you probably know it might anyway. I might be rambling, it is 4:30am 

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I see what you are getting it, but wouldn't any prolonged higher temperature due to the increased thermal mass of a thicker test piece be largely offset by the  cooler air circulating around in the kiln atmosphere?  I wonder which would be dominating?

 

I guess the only way to know would be to put a series of test tiles (say at least 5?) of the same clay in increasing thickness into the same place in the same kiln and the same firing, etc. and see what happens....   

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  • 3 weeks later...

It might also be possible to make a box on your kiln shelf out of hard fire brick. Place the thicker slow cool tiles inside this box and the thermal mass of the hard brick box should cool much slower than the rest of the kiln.

 

Just be sure to put cones in the box too.

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