What’s the hottest temperature that I can safely unload a bisque kiln?

[GEP]

I’m in a time crunch here. I’d like to hear other’s experiences about what works and what doesn’t work. 

[Pres]

When I was doing Penn State Festival, I would at times fire overnight, and unload the following morning. Pieces were too hot to do with out gloves, but all did survive. I did not have crazing on them, but the zinc glaze was matt. Most of my pieces were large jars and vases back then with some bowls and mugs. However, I would be hesitant about removing large flat platters because they cool so quickly in open air. .. . large surface areas disperse heat quickly. Back then I opened the kiln by feel, no thermometer, but again, most of what I did was by feel and sight when it came to firing.

 

best,

Pres

[Callie Beller Diesel]

I think once you’re past quartz inversion, there’s a little more leeway for bisque than for glaze. The clay body isn’t as at risk by itself as the glaze/clay combo is. 

My usual rule of thumb is the same number of hours going down as going up. So if the firing takes 10 hours, it gets 10 hours undisturbed before I pull 2 peeps to speed up the cooling. Depending on the weather (my kiln is outdoors), I open the lid wide about 2-4 hours after that.  I usually use a pair of leather garden gloves to unload with, as pieces are uncomfortable to touch, but they’re in no danger of succumbing to thermal shock. 

[GEP]

Thanks @Callie Beller Diesel. I actually pulled the peep plugs about 5 hours after the firing, at around 1200 degrees (farenheit). Do you think that was too soon?

Edited December 2, 2022 by GEP

[Mark C.]

The trick for quick cooling is no let cold air in. No matter what typoe of kiln.Electrics are easier as they are essentially sealed up. The lid lets the heat up and. out -I keep the plugs in and cover any holes and open the lid with gloves.

[Mark C.]

Its cruch time here as well. Shop heater is roaring-trimming like crazy bisque loading and then ....... I'll put up a post about this strange deal

[Callie Beller Diesel]

@GEP I tend to be paranoid about quartz inversion. That said, I’ve accidentally left the peeps out before, and I put them back in to ease the cooling through that 1063 F zone, but you could probably pull them again once you’re comfortably through it. 

 

Edited to add: I personally wouldn’t play around with a glaze firing doing this. I know from experience I get crazing that wouldn’t normally occur when I crash cool. But again, with bisque you’re not worried about that clay/glaze interface. 

[neilestrick]

Quartz inversion issues take a relatively quick drop to be a problem. You can leave 3 peeps out from the peak temp and you are still very unlikely to have anything crack. I open my kilns wide open at 350F on a regular basis without issues. I've pulled pieces out at 500F, but that makes me nervous. I'll often prop the lid and inch at 500F and it doesn't hurt anything.

[GEP]

Thanks @Callie Beller Diesel! Well, the kiln has already dropped below 800F, so I guess I'll just leave them out now, and hope for the best. It doesn't seem to be cooling too much faster than if I had left the plugs in (maybe 130 degrees per hour instead of 100 degrees).

And thank you @neilestrick for the added perspective and information!

Edited December 2, 2022 by GEP