How do I fire-down on a manual kiln?

[Diz]

HI Everyone,

With the upcoming week in MN being in the deep deep freeze (daytime temps below zero and wind chills of 40-50 below) I have a glaze firing that I need to do with my manual Skutt kiln.  I will be doing a glaze fire to cone 5.  My Skutt has 3 knobs (low,med,hi). The garage is unheated, but I can get the room somewhat warm using an area heater.  During a normal firing, I can usually unload my kiln after 22-24 hours of cooling. I have heard of 'firing-down but don't know the schedule of times or how fast the temperature drop should be.  I do have a pyrometer that I can use.  I'd appreciate some of the good info that everyone so freely  shares about how to do this.  Once kiln reaches temp (and turns off), I then turn it back on, begin to turn the switches down(off) in some order. I know I can gradually turn my switches down until a certain temp is reached but don't know if this is time or temp drop regulated.

Help please - or shall I just wait to fire?  I could make my delivery a week later, but I assume firing-down would still be necessary.

This site is wonderful help to those of us who are not fully trained in ceramics.  THANK YOU!

Diz

[Mark C.]

Go to home page and do a search as this has been covered a lot before look for (Firing down)

[neilestrick]

Slow cooling only affects glazes above approximately 1450F, and when the kiln is above that temp the outside temperature won't affect the cooling rate enough to matter. So don't worry about firing down because it's cold outside. Adding a slow cooling cycle to your kiln is more likely to affect the glazes than naturally cooling in a cold environment. Where you do need to be careful is at the low end of the firing, as you don't want that below-zero air rushing in on 500F degree pots. So keep the kiln closed up until it's cooled to 150F or so to be safe.

When you do have a chance to experiment with a slower cooling cycle, I would start at about 175F/hr and go from there. Some people slow cool from the peak, others let it crash to about 1950F or so before starting the cooling cycle. Either way, run the cooling cycle down to 1450F. In a manual kiln it can be difficult to control just how slow it cools, but a good place to start is to put the kiln back on medium and see how that goes. You'll have to be there when the Sitter shuts it off, then lift the weight, push the power button in, and gently lower the weight so that it doesn't kick it off. 

[Diz]

Thanks Neil!  Your info is what I needed.  My search for 'firing down' didn't really show much about temps .  I was fearing too rapid a cool that would result in crazing and/or cracking and thought I had to slow cool to avoid crazing and cracking.

 

 

[Pres]

I have been firing my L&L for years with slow cooling all manually with the help of a color heat chart. I have also found that I can slow the natural cooling of the kiln by replacing my lid with a much thicker lid that will keep heat from escaping out the top as much. I start my slow cool by turning down my switches to 80% after reaching cone 6, I leave it there until the kiln heat color is yellow, then turn down to 50% until the kiln color is red orange, then I turn off. This is my cooling set up, you may be more accurate with a pyrometer, but between the two color of heat and the pyrometer you should be able to handle a schedule that will meet your expectations.

 

best,

Pres

[Callie Beller Diesel]

You shouldn’t have to do anything special to your cooling cycle just because you can do that fun thing with the boiling water turning into snow in an instant this week. 40* (C or F) difference isn’t actually a lot to a pot in a kiln as long as you’re not opening it at quartz inversion, like Neil said.
 

Those of us with manual kilns don’t have to worry about getting the thermocouple warm enough to read in order for the kiln to start either. As long as your kiln is sheltered, the only reason to have a space heater is to keep from freezing valuable appendages off whilst loading, which is still a good reason, really. I do recommend a pair of fingerless gloves, and layers are better than a big bulky jacket that can catch on kiln brick.