What Does Slow Cooling A Kiln Get You?

[Pugaboo]

I've been seeing references to slow cooling more and more lately. Why would you do this? What does it do for the pieces? I'm just curious and wondering if it's an improvement in color, diminishing of pin holes, a more even color, etc?

 

Thanks for helping educate me in this!

 

T

[bciskepottery]

Some glazes benefit from a slow cooling; others do not.  Depends on what is in the glaze.  Iron reds show better depth and color, also more crystal development.  At what temperature you slow cool to also affects the color and melt. 

 

http://ceramicartsdaily.org/firing-techniques/electric-kiln-firing/firing-up-and-down-2/

[MatthewV]

It is harder for me to know what results I might get without a controlled cooling. I programmed my firing schedule and now just use the same one again and again. After a little tuning, I have been consistently happy with the results.

 

As Bruce said, it has an influence on development of the glaze. Holds around 950°C are targeting iron -- there is an iron crystal phase transition around this temperature. I used the word influence because the results are not "better" in a comprehensive way.

In a physical chemistry way, the transition is the same as the well know quartz inversion. The only difference is with iron (and some others) the lattice can be trapped in different ways and can be seen in normal conditions.

 

If you like iron glazes, slow cooling is something to try.

[fergusonjeff]

I thought slow cooling was going to do some amazing things to my pretty standard cone 6 glazes.  I use a lot of layered rutile glazes.  They give nice flowing colors under a normal electric firing.  I think they need the crash cooling to freeze the glazes in a flowing look.  The slow cooling seems to have allowed the colors to blend together and many of the glazes went into a dull single matte color. 

 

I did have a white glaze that was usually more clear in my normal firings.  Under slow cool it came out a really nice matte white.  So, it really depends on the amount of lending and crystal development. 

[Guest JBaymore]

Most of the visual effects that people see with large gas kilns that they attribute to "reduction" actually come from the typically slower cooling profiles that stem from the better insulated, lower surface area to volume ratio, larger thermal mass which such kilns tend to have.  Not the reduction reactions.  Small kilns (like the typical studio potter electrics) tend to cool off at the upper reaches of the firing range very quickly.

 

If you are wanting gloss glazes......... cool quickly.  If you want more varigation of the surface, semi to matte surfaces... slow the cooling.   

 

As has been said above... not all glazes will be impacted by slower cooling.  But al lot are.  What you are getting is microcrystalline crystals floating on the surface of the glaze.  A lot of glazes have the right combination of oxides present in the correct amounts to facilitate this effect.

 

Don't think of a "firing profile" as going from room temperature up to peak... and then magically "done".  Think of it more like from room temperature up to peak and then down to room temperature.  It is a paradigm shift. 

 

Computerized controllers have made "firing down' easy.

 

best,

 

.....................john

[neilestrick]

I have a glaze that actually has more gloss when I add a cooling cycle. I think it's because I slow cool from the peak temp, so it gets a little more time at full melt, almost like soaking.

 

For me the greatest benefit of the cooling cycle is getting the same cooling rate from all 3 of my kilns, so I get identical results regardless of the kiln size.

[Chris Campbell]

For me, slow cooling has lowered the loss rate when firing porcelains. Slow, controlled cooling has also given more evenly fired loads.

[PeterH]

Pictures are often informative. Have a look at the Slow Cooling article in the freebie at:

http://ceramicartsdaily.org/free-gifts/electric-kiln-firing-techniques-and-tips-inspiration-instruction-and-glaze-recipes-for-electric-ceramic-kilns/

 

... and the article on iron reds at:

http://ceramicartsdaily.org/ceramic-glaze-recipes/glaze-chemistry-ceramic-glaze-recipes-2/the-many-faces-of-iron-an-exploration-in-cooling/

[NancyAmores]

Most here use their own glazes, but for commercial examples the Coyote site shows all of their glazes at both slow and regular cooling, if you click on a glaze pic it shows them from both schedules: coyoteclay.com  Like Neil I only fire down to try and make my test kiln give results closer to a bigger kiln.

[glazenerd]

If you are intending to use glazes that require a soaking period on the way down from peak: they do make electrics built for such use. My primary crystalline kiln is 3" brick with 2" fiber: it cools very slowly on its own. Absolutely not necessary unless you plan on firing glazes that require soaks.

Nerd