Cone 6 Firing - Electric Kiln with Sitter

This is my 5th firing or so with glaze. I'm using Cone 6.
Yesterday I started my typical glaze firing however I'm having
problems getting the kiln up to temp.
Here's my process:
Cone 6 into my sitter
Bottom 2 peep holes plugged
Top peep hole open
250F - 1 Hour
1676F - 2 Hours
1926F - 2 Hours
2200 - 3 Hours
Usually during that 3 hour time period my kiln sitter will shutoff and
it's all done. This time however, it's been going for about 11 hours
and it's till not turning off.
Should I close up the top peep hole? Should I open up all? Is it
getting enough oxygen? VERY NEW to this.
Thanks
-Steve
Reply to
SKrause
If you are only venting your kiln with the peep holes then you vent the kiln when gases are being released. The Peep hole should be closed up after that. I vent my kiln the entire time to keep the temperature even and because that is what the manufacture recommends but that is with a down draft vent. Having the peep holes open is not good in general because you are getting cold spots in your kiln with them that way.
I'm very confused by your table - here is what one of my cone6 firing and the timing typically is
Glaze Cone6 72 100 220 1.48 350 2000 5.09 150 2180 0.42 hr hold 1.20 500 1900 0.56 125 1400 4.00 12.74
Note that it takes 5 hours to get from 220F to 2000F. I'm holding it for a long time (around 25minutes) in this firing but it is under cone6. I ramp down slowly after 1900F. My total time firing is almost 13 hours.
Reply to
DKat
Sorry - forgot the header
Temp change/hr temp hold time 72 100 220 1.48 350 2000 5.09 150 2180 0.42hr hold 1.20 500 1900 0.56 125 1400 4.00
Reply to
DKat
To add to Donna's post, I agree about closing the peepholes after the initial burning-out stage. However, I seriously doubt that the open peephole is the problem here. If your kiln used to hit cone 6 on the above schedule, it should have no trouble with the peep open. (A marginal kiln that could just *barely* make it to cone 6 with the peep closed might be different, but I'd have expected to see a much longer firing time in that case.)
And don't worry about getting enough oxygen. No oxygen is needed to reach temperature, it bascially only affects the appearance of certain glazes. But any ordinary electric kiln, no matter how well you seal it up, will have plenty of oxygen for this purpose. In general you need a fuel-burning kiln if you want to get rid of the oxygen (called "reduction" instead of "oxidation"). They get that by adjusting the air-fuel ratio so the flame uses up all the free oxygen in burning the fuel, leaving none to react with the glaze.
Best regards,
Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis
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Bob Masta

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