Cone 6 Firing - Electric Kiln with Sitter

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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


Re: Cone 6 Firing - Electric Kiln with Sitter
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.

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Re: Cone 6 Firing - Electric Kiln with Sitter
Sorry - forgot the header
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   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
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Re: Cone 6 Firing - Electric Kiln with Sitter

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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
 
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