Tuesday, December 11, 2012

Fourth Firing Lessons

First peek into the kiln
I may have gotten a little carried away by packing my kiln with so many pots. My efforts to try and sort out some issues I was having did not include the assessment that packing my kiln the way I did would make it reduce much harder than I thought it was. The reduction of the kiln, when the oxygen is cut off, causes the iron in the clay body to be drawn to the surface, making the pottery look darker. The porcelain ornaments remained white because porcelain has no iron in it. How do I usually know it is reducing? Usually I have gotten back pressure in my front firebox, which I did not have as much of this time, and that falsely made me think I was doing okay. Sometimes I will also see little black wisps of smoke coming out of crevices at the top of the kiln when it is reducing really hard. I also did not see as much of that this time, but because the shelf was so densely packed in front of the flue, I think it was naturally reducing away the whole time!
Dark and shiny pots
On the plus side, I had little to no dry ash in this firing, and the cool corner was closer to the rest of the kiln than it has been in the last firings. I ended up starting to salt around cone 8, continuing through cone 10, and soaked the kiln for an hour after the final salting. All of my glazes fluxed smoothly and the salt coverage was pretty profound in a few places. We reached cone 11 in most places and the total firing time was even a little shorter than the last one! Here's to looking forward to firing number five!


Dennis Allen said...

It's always something isn't it? All that tight stacking was just like an internal damper. Personally, I like 'em.

Dan Finnegan said...

I LOVE those warm, rich surfaces!

Liberty Stoneware said...

It is always something, always learning! That's a good way to think of it, as an internal damper. I definitely think I will purposefully fire a kiln like this a few times a year to have some warm browns, and the surfaces are really great. I have some ideas for warm brown kitchen ware...I think I may be able to back off on the salt though as some parts may have gotten a little carried away. Shiniest kiln yet though! I crashed cooled to 1650 and then capped the chimney, didn't lower it any further and let it cool for two days.