A Guide to Glazing Chosen Karatsu

There is a new video up on the Karatsupots youtube channel. On it, I explain the process of glazing Chosen Karatsu ware, from applying the ame glaze, to trimming the ame, and subsequent application of the wara glaze.

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.

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

Let them eat cake

Here is my latest pot porn for you: freshly stamp milled, slaked, and filter pressed cakes of Izumiyama porcelain. 150kg. 


Not for the faint of heart, Izumiyama is hard to work with. It is non plastic and likes to crack during drying, impossible for slab work, and deforms easily. And it costs more than twice as much as Amakusa porcelain from Kumamoto. Most porcelain artists in Arita and Imari switched to using Amakusa porcelain long ago because it’s much easier to work with, doesn’t crack, and fires whiter. 


BUT! The beauty of Izumiyama in the wood kiln is absolutely undeniable. It fires to a soft ivory white and blushes in very subtle shades of peach. The surface is deep and translucent and vitrifies as low as around 1230C. 

Tomorrow morning first thing, Peter the Pugger will be getting a major workout!

Gas Firing 2016.02.20 Comments and Notes

This firing of the kiln went too long, resulting in Orton cone 11 flat.  Ideally, it would be cone 11 touching, then sagging a bit.

Upon unloading the kiln this morning, one thing was immediately apparent: the right side was far more reduced than the left. Yellower glazes and more slumping. Even on the left side there was some slumping, because of the excessive temp., and because of the clay which contained some low temp high iron clay to help seal the ware against leakage.

Left side, sagging only slightly, white surface.
Left side, sagging only slightly, white surface.

Right side sagging badly, white glaze turned yellow.
Right side sagging badly, white glaze turned yellow.

Chosen Karatsu came out pretty good, but the white was on too heavy, running down the pots too much.  It still came out looking ok because of the clay.

Most of the teabowls warped or sagged, so I only get to keep 2 or 3 of the 15. This is why teabowls are expensive, kids…IMG_3399 IMG_3398

All in all, not a bad firing, but need to adjust clay bodies, and pay closer attention to cones. Also, figure out the over reduction on the right side. It might be that one burner that sounds a bit off.

Kakewake CG bowls
Kakewake CG bowls

guinomi, need more sand in the clay
guinomi, need more sand in the clay

crystals, only grew on the right side, where reduction was strongest.
crystals, only grew on the right side, where reduction was strongest.

cylindrical tea bowls
cylindrical tea bowls

yunomi
yunomi

shells on feet
shells on feet

IMG_3437

saggared and much improved.
saggared and much improved.

porcelain, saggared
porcelain, saggared

IMG_3464 IMG_3463 IMG_3462 IMG_3460 IMG_3459