Question About Kiln Cooling

[Rick Wise]

I know that kilns are sometimes "slow cooled" to create or enhance certain desired effects such as crystal formation.  I also know that  "abrupt cooling" should be avoided because of the danger of thermal shock cracking.  My question is:

At what temperature are the effects of slow cooling no longer expected?  Am I correct in thinking that at and below about 1000 F the only concern is with "abrupt cooling" and that any "slow cooling effects" have been achieved (or not)?   Put another way, are all of the "slow cooling" effects seen at relatively high temperatures well above 1000 F?   

At 1000 F my only concern with cooling is avoiding thermal shock -- right?

[neilestrick]

1450F is about as low as you would get any effects from slow cooling.

[liambesaw]

16 minutes ago, neilestrick said:

1450F is about as low as you would get any effects from slow cooling.

I'd say right around 018, so a little cooler. I've had some iron and titanium glazes shift color during lustre firings.

[Dick White]

I have run some "fully instrumented" firings in several kilns with a logging pyrometer connected to a computer recording the temperature every minute, both on the way up and all the way down. At around 1500F, the natural cooling rate will be only about 150F/hour, getting slower all the time. So, by then, trying to maintain a slow cooling via the controller useless. And, as others have pointed out, not much is happening to most glazes at that point anyway.

[neilestrick]

1 hour ago, liambesaw said:

I'd say right around 018, so a little cooler. I've had some iron and titanium glazes shift color during lustre firings.

That's a re-firing situation, though, not a slow cooling situation. They don't always behave the same.