Still confused about first firing in new L&L kiln

[Roberta12]

@PotteryPam My L&L started firing too hot about 2 years ago.  I had gotten lax about putting cones in. When I started getting bloat issues with a couple of clay bodies, I started using cones again.  The cone 6 program was firing to 7.  I changed elements, thermocouples, checked wires...... but it was still firing hot.    I reduced  firing to cone 5 instead of 6.  I put in a 15 minute hold.  And...in order to obtain as much consistency as possible, I bought cone plaques, kiln washed them so I can reuse them, and they go in every load.  My cones show I am getting about a 5 and a half.  The 6 starts to bend.  The firings are a little shorter, glazes look good, pots seem to be vitrified.    Since my kiln is 12 years old, I only have fast glaze and slow glaze as options.  I almost always choose slow.  (unless there is a deadline!)  Ceramics, every single aspect, is a way of keeping us humble.  

[PotteryPam]

Thank you.  Yes it is a big learning curve, but didn’t expect a brand new kiln to be so off.  Perhaps their firing schedules were not developed with the 3” bricks in mind.  L and L support suggested firing a cone lower.  

[PotteryPam]

Here are the 5,6,7 cones.  Even though they are large self supporting cones, I put them in a clay holder because the 04 cone in my first bisque fire fell over and fused to one of my pots, and ruined the rim.  Thanks for your help and attention!

[Bill Kielb]

6 hours ago, PotteryPam said:

Here are the 5,6,7 cones.

Interesting, thanks for the pićtures. They are super melted but hard to tell, it appears the cone on the left in the picture (cone 5)  is facing cones 6 & 7 so it will melt on top of them, and it did! Since this is an important calibrating type fire I would suggest setting cones so they melt away from each other. I am not a fan of self supporting cones being elevated on clay as it often changes the tip height slightly and can change the angle slightly if not installed perfectly flat. Maybe instead of a wad of clay, kiln wash or a touch of alumina for the shelf beneath the cone and set cones so they fall away from each other. Maybe for a test fire with some extra shelves or simulated loading to see how this performs with a typical load.

So for accurate calibration I suggest you test where this really ends before entering offsets. The cone pack in the picture likely does not confirm accurately because they melted on top of each other.

Typical cone pack below, Guide ( melts first), Firing, Guard ( should not melt much) Sue McLeod has a nice pdf on cone packs, the picture below is from Sues website and can also be found here: https://suemcleodceramics.com/how-to-make-a-cone-pack/

 

Edited 4 hours ago by Bill Kielb