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7000 Elevation & affect on firings in electric kilns

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I bought my first electric kiln and did my first bisque firing this past weekend. The kiln is a L&L Easy Fire. I did a preheat for 6 hours then did the slow bisque program. I had 06 cones on the bottom and on the top shelves. Final reading was 19.11 hours and 1824 F. The cone on the top was flat and the bottom was mostly flat with a slight curve where the top hit the base and curved back up slightly. I live at 7000 elevation and I'm not sure what that does to firings. I believe the temperature was okay for 06 but not sure why the cones were flat. Should I make adjustments to the thermocouples?

Karen

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sometimes firings react to the eveness of the load. 19 hours to bisque is really slow. I lived at 3000 and worked at 6000 ft. The elevation does effect drafts in atmospheric kilns but should not..in my opinion... have any affect of radiating heat in an electric kiln. Keep notes...your thermcouple could be a little off. Watch your witness cones especially in the glaze...where the readings could be further off.

Marcia

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Guest HerbNorris

Marcia is right, the elevation will not have any effect on the radiant heat of an electric kiln; because there is no actual combustion occurring (as in an atmospheric kiln) oxygen concentration is not an issue.

What is an issue with the increased elevation is the boiling point of water, as you know; water boils at a lower temperature (around 199 F at 7k feet) due to decreased weight of the atmosphere/unit area.

Skutt kilns, when preheating, ramp the temp up at 60 degrees/hour until 180 F is reached, then the preheat hold begins. I believe L&L have a higher setpoint of 200 F. This is very close to the boiling point of water at that elevation, so you probably have to take a little more care to dry your ware.

Also, since it takes Skutt/L&L kilns three hours to reach the preheat temp, that time is added to the total firing time. Three hours ramp up plus six hours preheat hold plus bisque fire time comes out to 19.11 hours. The packing of the kiln could also add to the time.

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Our studio kilns are L&L; we bisque at ^05 with a 2 hour preheat and 30 minute hold using the Slow Bisque firing program. Firing time is generally in the range of 14 to 15 hours. Considering your longer preheat, 19 hours may be acceptable. Your L&L kiln manual has a number of firing charts showing estimated times at various cones. Compare to what the manual says. I also do not believe altitude will affect the time for an electric kiln firing.

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L&L also has 60 degrees an hour for the preheat but does hold at 200. The pieces were very dry and I thought 6 hours was probably overdoing it but I wanted to play it safe. I looked up the firing profile for the slow bisque program and it said it should take a total of 12.73 hours so 19.11 sounds too fast if it takes over 3 hours to get to 200 then hold for 6. The thickest piece was a 1/2" slab and it cracked. All other pieces were small and appear to be fine.

 

Next time I'll do a custom preheat at 180 to keep it below 200 and program the bisque instead of using the slow bisque program and see if it makes any difference. I also sent an e-mail to L&L to ask them for their suggestions.

 

Do you use the witness cones as the true representation versus the temperature reached on the control? From my reading that appears to be the case. I'll also put in 3 cones next time - 05, 06, 07. The first initial firing to cone 5 seemed to be underfired but the kiln was empty.

 

Thanks for your replies.

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