Firing too long at lower cone a problem?

[Meredith Walker]

I forgot to plug my bottom peep this morning when I started my kiln, and my kiln was firing longer than usual at a lower cone. I estimate it stayed at about ^1 or 2, based on the firing color chart. So after what should have been about a 7.5 - 8- hour ^6 firing, after 10 hours it was still going. THEN I realized the plug was out, and put it in. It's still firing, & I'll check it in a few minutes to see if there's any change. (I can't see the witness cone.)

My question: is this going to be a disaster of a firing? What happens to glazes if they're held at a lower temp for a long time BEFORE they've reached cone? I know that soaking after reaching cone can be good -- but I've not had this happen before. My kiln is a 30+-year-old Cress, with no bells or whistles - totally manual.

Thanks.

[George Lewter]

If you have a kiln sitter keep firing until it trips as it measures heat work. If not, fire until cone 6 goes down.  You won't like a the outcome if you don't get past cone2.. Your long firing may improve your glazes 

[Meredith Walker]

Thanks, George. The kiln finally switched itself off around 4, I think, coincidentally just after I'd talked to our studio director here about the problem.Maybe I at least won't have nightmares tonight, thanks to your and his encouraging comments. I do wonder how the glazes will turn out - if something looks really interesting, I'll post it here.

[Norm Stuart]

Leaving both peephole plugs open is costly in terms of electricity, but apart from that the firing time with both peepholes open probably didn't accomplish much.  The real firing and heat-work didn't start to take place until you put one of the plugs back in.

We have a very over-powered kiln for its size, about 10 kW per cubic foot, and I doubt it could reach cone 1 with both peepholes open.  If you look at your kiln when the temperature reaches 2,000 F you'll see a fairly generous air gap between the lid and the kiln walls - and the soft firebrick is porous as well.  The last thing a typical electric kiln needs is more ventilation.

A few years ago we had someone fire a cone 6 with both peephole plugs out of our older lower power kiln with a kiln sitter.  Looking at the results, I don't think the kiln got much hotter than cone 04.  The person handling that firing had become convinced that both peepholes had to be open for an oxidation firing, because he read that all of the "dampers" of a gas kiln had to be open.  It took quite a while to convince him he was wrong.

Meredith Walker said:

Thanks, George. The kiln finally switched itself off around 4, I think, coincidentally just after I'd talked to our studio director here about the problem.Maybe I at least won't have nightmares tonight, thanks to your and his encouraging comments. I do wonder how the glazes will turn out - if something looks really interesting, I'll post it here.

[Meredith Walker]

Thanks, Norm. I didn't intend to leave the bottom peep open - I just forgot to put it in. Won't do that again! Now I just have to patiently wait until I can see results tomorrow.

[Meredith Walker]

Happy to say that this firing went just fine! Everything turned out as I usually expect from a normal firing. I've also tested my elements for burnout (using paper strips). All look okay.

[Nadine Mercader]

Let's see some of your wares!

[Meredith Walker]

These are from two separate firings  -    the blue spiral one went through the firing I described in my post. White clay, blue slip, white matte glaze. The green is Philly Green matte on Speckled Brownstone clay.