New L & L kiln -- first glaze load very overfired

[NanS]

Hi Wise People,  I have a new L & L e23S-3 kiln.  Previously I've only fired the test firing (Slow Bisque cone 5) and one bisque firing (Med Slow Bisque cone 05).  This week I did my first glaze firing, programed to "Medium Glaze" cone 6.  The test firing and the bisque previously both fired too hot -- see photos below.  In all of my firings the middle shelf (out of 3 shelves total) was noticeably hotter.  I set a thermocouple offset of +12 degrees F for my glaze firing.   I was trying to be cautious and hoping I would end up close to Cone 6.  The glaze firing was quite overfired even with the offset as you can see from the two photos of my cones below.  It actually looks like the glaze firing was even more overfired than my previous two firings.   The controller showed that the final temp was 2234 F, and the firing took 8  1/2 hours. I had the vent on for the whole firing. The questions I have are:

1) Is this level of over firing considered within the range of normal?

2) To what degree should I offset in my next bisque / glaze firings, and should this be a cone or thermocouple offset? 

3) Could there be a problem with my kiln that needs addressing other than doing an offset?

4)  Does this look like my glaze firing was almost to cone 7?   Unfortunately I put the cones too close together to see how they would have bent without leaning on the cone in front.   The test pots and test tiles in the glaze firing came out very funky as you can imagine.  For example, I used a lot of white slip on my brown stoneware clay.  Much of the white slip was burned off and almost non-visible after the firing, but especially under certain clear glazes.  (I tested 4 clear glazes.)   Luckily none of the glaze dripped onto my shelves, and I had no blistering. The colors of 3 commercial glazes that I tested were very off.  Two tests I did by modifying two clear base glazes with  6% zircopax came out clear instead of white.

Thank you very much in advance for helping me  figure this out!

 

[neilestrick]

It looks like your cone 6 firing got to about cone 7. Your 05 bisque firing was just slightly over fired, probably not enough to worry about. It's not uncommon for them to fire a little hot at the cone 6 range for some reason. I have to program my kiln to 2190F for cone 6 instead of 2232F. You have several options to dial it in:

1. Set a thermocouple offset. I wouldn't do this, though, because the bisque firing was pretty close to where it needs to be.

2. Set a cone offset for cone 6.

3. Do a custom program, setting the peak temp to whatever it needs to  be at to be accurate. I would start with it about 20-30 degrees below cone 6 (2232F). You can copy the firing schedule in your manual for most of the firing. Just be sure to set the last 200F degrees to a rate of 108F/hr.

[GEP]

When using L&L’s Easy-Fire programs, the final temperature will vary depending on how long the firing takes. If for example you have a loose-ish kiln load and the firing goes faster than expected, the controller will add more temperature to the end in order to compensate for the shorter time. In my experience these compensations are not all that accurate, and will result in overfirings and underfirings. In other words, there’s nothing wrong with your kiln, it’s doing what it was programmed to do, just not doing it very well. The way to get more accurate firings is to follow Neil’s suggestion #3 above. 

[DirtRoads]

Just changed entire set of elements and all 3 TC's.  Looked through manual and can't find exactly what to do?

Fire Cone 5 (Cone I use) on .... Slow Glaze?  With witness cones to test?

Somewhere I read to fire slow to 1000 degrees to situate elements.

[neilestrick]

15 minutes ago, DirtRoads said:

Just changed entire set of elements and all 3 TC's.  Looked through manual and can't find exactly what to do?

Fire Cone 5 (Cone I use) on .... Slow Glaze?  With witness cones to test?

Somewhere I read to fire slow to 1000 degrees to situate elements.

A bisque to cone 04 will be fine. You don't need to do the long 'first firing' program you did when you first got the kiln.

[NanS]

Thank you neilestrick  and GEP   !!   This is super helpful feedback.   For my next glaze glaze firing I'm going to go ahead and make a custom program based on Neil's suggestion.  

Thanks again!

 

[DHP]

Hello!

I just did my first firing for my new easy fire 18t3 and think it over fired as well. 

Neil what do you mean by “Just be sure to set the last 200F degrees to a rate of 108F/hr”. How do I do that?  
 

thanks!

[Pres]

@NanS, I had the same problem as you a few years ago when firing my new L&L. I followed Neil's instructions after some back and forth and now my firings are consistent at ^6. Not hard to do, and as I came from an all manual kiln. . . .I get more sleep at night!

 

best,

Pres