stoneware

Chosen Karatsu 11/17/2020

bottle

Today I want to post the results and thoughts about the latest CG firing. This firing was more successful than the CG firing in March, but I’ve uncovered some other problems, namely uneven reduction. My first thoughts on troubleshooting this are:
1. possible leaking kiln door fiber seal?
2. open the shelf placement to promote more air circulation?
3. Check the burners on the over reducing side, and possibly adjust secondary air?
4. look inside the car to see if any airways are obstructed?

Next, a look at the before/afters, with special attention to the thickness and trimming of the rice straw ash glaze:

Next, the keepers:

Thoughts:

-The glaze thickness was about right, and the interior glaze thickness was about perfect.

-The firing was too hot in the top half of the kiln, resulting in most of the loss. Also, over-reduced areas exacerbated this issue.

-Perhaps both glazes are a bit too runny at cone 11 and need adjustment.

-The middle and upper rear right was VERY over reduced, this needs looking into. Multiple possible causes.

– Use shells on the feet even when not in doubt about drips. Much of the loss in this firing could have been avoided if there had been something between the bisquits and the pots.

Propane CGFiring Notes, 2020/03/16

Gas kiln firing, 2020/03/16. Chosen Karatsu and Madara glazes. 3 types of Madara glaze from old buckets in which the exact contents were largely forgotten.

The normal madara glaze ended up being too low in silica, and going clear in most cases. Shirakawa madara pinholed in most cases. I’d forgotten about this behaviour. New Madara glaze test shows good color, but also, low in silica perhaps, needs more straw ash added (1kg).

Shida madara much too clear, only showed white where very thick. Maybe miscalculated when mixing the glaze? Add more Shida (2kg?) to overall batch. Test again.

  • Opening the kiln
  • Good katakuchi @cone11 flat, but pinholing with the Shirakawa Madara glaze.
  • Soft cone 11 on the bottom. Good. Madara glaze too thin, or not enough silica, or both.
  • Yes, probably not enough silica
  • a damn shame. hammer?
  • Left:Shirakawa Right:Normal
  • NormalMad to melty, need more silica.
  • ShirakawaMad pinholing even at the bottom cool part of the kiln.
  • Lovely reduced cups. BinchoTan, shells
  • Super. Nice refire color in heavy reduction plus cooldown reduction.
  • Yessssss…
  • sample tiles @cone11 flat (cone 12 equivalent?)

Gallery

Cool Color

This last firing of the gas kiln I used draw rings to get a better idea of when certain glazes matured. I’ve known this for a while, but was struck again at how colorless and boring the colors of the glaze and clay were when yanked and doused in a bucket of water. So colorless, in fact, that two different glazes appeared to be virtually identical when crash cooled. The sandstone body, also, is an uninteresting greyish white.

left: sandstone/ash 7/3 right: high silica ash / oak ash/ spar 6/4/3

Here are those same glazes after firing for 16 hours and cooling slowly in the kiln for 36 hours. (first two pics are same glaze and body as the ring on the left, above. Second two pics same as the ring on the right.)

nor
sandstone/ash

Notice a difference? Not only in the quality of the glaze surface, which is distinctly more blue with patches of sugary white, but also with the clay body color development?

nor

The changes in this glaze are even more pronounced. No longer a colorless clear, but a soft creamy white translucent.

Last is a black glaze which was a featureless glossy black on the test ring, but which given time, developed into a rich black/brown with some crystal growth.

So, with that in mind, I wonder how nice these glazes and clay body would look after a 96 hour cooling period in the wood kiln?

On an aside, here is one of five toggle buttons I made and fired in a saggar with rice husks and cockle shells. Same body as the cups above 70/30 sandstone/Izumiyama porcelain. Approx. 6cm

Spring Firing Results

Ok, lots of things to say about this last firing, but with the studio show starting tomorrow I just don’t have time for a long post. Here are pictures instead, commentary and contemplation about these results will follow in a few days…