Newbie: Kiln Over Or Underfired?

[sheppard.lin]

Hey all! 

 

First time posting here. I'm new to firing, and i've been having some difficulties getting my kiln to fire to cone 6 properly. 

 

Here's my problem: When I check the cones at peak temperature (2180 in my case), the cones are not bent properly yet. Last night I just let it cycle down anyway. However, when I opened my kiln at the end of firing, the cones were overfired (at least at the top of my kiln). I've been slow cooling, so is it possible that the heatwork as the kiln fires down is actually causing the cones to bend further even at lower temps?

 

Firing Schedule:

 

220/60 - 100 degrees/hr

2000/0 - 350 degrees/hr

2180/15 - 108 degrees/hr (still not getting my kiln up to 2192, but that might just be a problem with the PID or thermocouple)

1400/0 - 125 degrees/hr 

OFF 

 

I have no idea how to tell if my pieces are over/underfired because of this. Do I base it on what the cones were doing at peak temp, or what they looked like at the end of firing?? 

 

 

[Min]

Hi and welcome.

 

Always go by the cones, they have had the same heatwork as the pots. You go by what they look like at the end of the firing. I find that firing down with my schedule and double holds does have a slight increase in the heatwork on the pots but not that significant. Were the cones you looked at the ones on the top shelf that overfired after the soak at 2180? It's common for electric kilns to fire unevenly if not using a multi zone controller. Just have to learn how to stack the kiln with more mass in the hot areas and less in the cool, cone packs on every shelf until you get it figured out. (that looks like the slow fire program from Digitalfire for rutile glazes?)

[neilestrick]

When you say the cone wasn't bent properly at peak, was that before or after the hold? The hold will adda lot of heat work. Slow cooling from the peak temperature will also affect heat work. So you either need less hold, a lower peak temp, or add a crash cool from the peak down a couple hundred degrees before you start the slow cooling.

[sheppard.lin]

Thank you both! I will try loading the kiln differently to even it out. The cone was not bent properly even after the hold. I was hoping the hold would bend it, but it didn't. I think you are right about the cooling! I will try crash cooling for a few hundred degrees, and see if that works. It makes sense that that would be the issue.