Category Archives: glazes

Scoring Goodies

I made a trip out to the mountains in Minamihata yesterday with my mentor to collect materials for pots and glazes, and we stopped by an old kiln site as well.

We were able to collect a good amount of feldspathic sandstone, weathered feldspar, and the ever popular grey stuff (don’t know what its real name is).

First, here is what we collected that will become pots and glazes this year:

The lot of it
Grey stuff. This is softer than rock and can be stamp milled or pot milled easily into a fine slurry. It has a lot of iron, and I use it as a glaze ingredient, as a slip, or as a pigment for decoration.
Sandstone. This has more iron than I’d normally like, but beggars can’t be choosers. It takes the place of both feldspar additions to clay bodies as well as grog. I like it because it helps the body vitrify, but gives it texture as well.
More sandstone.
Glaze stone from near Okawachiyama. I’m not sure but I believe this is the glaze stone used in Nabeshima celadon. I look forward to testing this.
Closeup. You can see the feldspathic translucent pieces in the matrix, surrounded by the white powdery matrix. I think the white powdery part is high in silica, but again, need to test.
Found this in the same place as the Nabeshima glaze stone. This looks to be more pure feldspar. Very curious to see how it fires!

On the way to one of the collecting sites, we passed two old Karatsu kilns, Fujinokawachi and Kayanotani.  I was surprised because they are separated by no more than 70 meters or so. These were big kilns. Kayanotani was a 22 chamber climbing kiln 52 meters long! Between them, there were probably hundreds of potters working. We couldn’t really access Fujinokawachi, but we were able to walk around on the hill where Kayanotani once stood.

Access to Kayanotani. You can see the faint grassy steps up the hill, just to the left and down a bit from the tree.
Sign board standing at the entrance to the kiln site. The shard pile extends up and down the hill to the left of the sign.
The outside surfaces of some coil and paddle flasks. Fujinokawachi and Kayanotani are both known for their fine coil and paddle work.
Interiors of the same. Note the different clays used and the different patterns created from the paddling tools.
Hillside littered with shards and chunks of kiln wall and kiln furniture.
The feet of some ash glazed bowls. The clay is quite light in color, and really vitrified.
Detail of some flask lips. On the one, you can see some bubbling in the glaze because the clay body started to bloat. The coil and paddle clay bodies were quite varied, but much of it seemed to contain high amounts of organic matter
More bowls. One in a light clay body, the other much darker. Again, vitrified and hard. All of the trimmed pieces I found were trimmed with an economy of movement. There is no wasted time in the trimming here.
Detail of another foot. Gorgeous clay, and lively trimming.
Interior detail of bowl directly above. Note the beautifully folded over and compress lip of the piece stuck to the inside here, and the glaze window.
Paddled Chosen Karatsu flask. I wish I could get those blues!
Detail of flask neck.
Detail, lip.

Overglaze tests with iron pigment

Here is the original test cup (r), and one pulled from the last firing (l). The first cup was refired to cone 5, the second to cone 6. I was worried with the extra heat that the overglaze brushwork would bleed or run, but it didn’t.  
One thing I like about this overglaze deco is that it allows me a ‘second chance’ for decoration when refiring this kind of work. The other is that it allows for finer detail showing up in the final product. Underglaze iron tends to get absorbed into the glaze and/or clay body, so the finest lines become obscured or transparent.

2016-03-20 Glaze tests 釉薬の実験

Fired with cones 6,7,8 on top and bottom shelves. Pyrometer at middle shelf, didn’t display over 1215C.
Hotter on bottom than top. By cone, looks like cone 9+ on the bottom, cone 9 at the middle, and cone 8+ at the top.

Reduction strong at top shelf, weaker at middle and bottom.

棚三段、上、中、下。 オートンコーン6,7,8 使用、上:下置。温度計は中に。焼成中の温度計は1215Cを超えずが、上は8番コーンは曲がって、ヘタレ。下は8番フラット。 実際の温度は下:9+、ちゅう:9、上:8+ とみていいでしょう。
上は還元効いているようだが、中:下は中性気味。

Unloading:

Bottom shelf, front. Mid shelf, rear left. Top shelf, rear right.
Bottom shelf, front. Mid shelf, rear left. Top shelf, rear right.
Top shelf
Top shelf
Mid shelf
Mid shelf
Bottom shelf
Bottom shelf
Bottom cones
Bottom cones
Top cones
Top cones

 

Clay : Ash Blends  (Lft, to Rt.:  Bott.,Mid.,Top)

Taku shiro 90 : Dobai 10
Taku shiro 90 : Dobai 10
Taku shiro 80 : Dobai 20
Taku shiro 80 : Dobai 20
Taku shiro 70 : Dobai 30
Taku shiro 70 : Dobai 30
Taku shiro 60 : Dobai 40
Taku shiro 60 : Dobai 40

 

Stone : Ash Blends    (Lft, to Rt.:  Bott.,Mid.,Top)

Sandstone 90 : Dobai 10
Sandstone 90 : Dobai 10
Sandstone 80 : Dobai 20
Sandstone 80 : Dobai 20
Sandstone 70 : Dobai 30
Sandstone 70 : Dobai 30
Sandstone 60 : Dobai 40
Sandstone 60 : Dobai 40

 

Clay : Ash total, plus 280g Shirakawa

Clay:Ash total +280g toseki
Clay:Ash total +280g toseki

 

Stone : Ash total, plus 280g Shirakawa

Stone:Ash total + 280g toseki
Stone:Ash total + 280g toseki

 

Everything dumped together: Stone:Clay:Ash:Shirakawa

Clay:Stone:Ash:Toseki total
Clay:Stone:Ash:Toseki total

 

Stone:Ash 70:30 from top shelf (cone 8+) in the sunlight:

Stone:Ash 70:30 @ cone 8 1/2
Stone:Ash 70:30 @ cone 8 1/2

IMG_3681

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

 

Fall 2015

has been busy.

I’ve gotten pretty far behind keeping up with the blog, falling into the bad habit of making small posts to Facebook. One of my areas of increased effort over the next year will be to work more on maintaining the blog, and getting it more integrated with other forms of social media. Trying to keep track of them all is like trying to herd cats.
I had made one promise to show before/after pictures for a couple of pieces, the first of which is the slab/paddle built sake chiller w/ feet and lugs:

IMG_2176
raw unglazed
IMG_2513
Fired piece, Chosen Karatsu style glaze. Matchbook for scale.
IMG_2518
Underside detail. Fired on shells, feet not touching the shelf.
IMG_2516
Glaze detail

 

The other thing I’ve been working on since early this year is getting a usable kohiki/clear glaze combination, because for some reason a lot of customers have been requesting white work. They have also been requesting black, so I’ve been working on getting a reliable semi matte black glaze. Mission not quite accomplished, but I feel I’m most of the way there. Here is the kohiki I’ve come up with and I am happy with it:

Kohiki cups. Cup on the left is unused. Middle has been used a bit, and right has been used a lot. The patina is beautiful in my opinion, and the fineness of the crackle is something I’ve been wanting for a long time in my work.
Various guinomi from 2015, mostly from the fall firing. Guinomi make great gyokuro drinking cups.
Various guinomi from 2015, mostly from the fall firing. Guinomi make great gyokuro drinking cups.
Seabirds on white.
Seabirds on white.
The other thing I have started doing is Japanese kana inspired brushwork
The other thing I have started doing is Japanese kana inspired brushwork, except with English. This cup is decorated with vertical English writing, a Goethe quote I like: “Whatever you can do, or think you can, begin it. Boldness has genius, power, and magic in it.” One of the other said: “Don’t be a dick.” These were more popular than I had anticipated and are currently sold out. Definitely making more!

Here are some of the pieces with the new black glaze. It seems to look best thin, and as with most glazes looks nicer over interesting wild clays rather than processed clays.

Type 1 semi matte black Katakuchi with black lacquer repairs.
Type 1 semi matte black Katakuchi with black lacquer repairs.
Type 1 semi matte black dish.
Type 1 semi matte black dish.
Semi mmatte type 2: two black glazes layered
matte type 2: two black glazes layered, makes a fatter glaze surface.

Chosen Karatsu Slabs

I had to make a batch of slab plates after the fall wood kiln firing, because every one of my slabs cracked in that firing. Turns out the clay I used was high in silica, and didn’t agree with the long wood kiln firing. The silica turned into cristabolite, and all pots made with that clay experienced shivering, or cracking, no matter what glaze they were paired with, and across a range of temperatures.

Forward a few weeks, and I’m frantically trying to get some replacement plates fired because this weekend is the fall open studio event, followed by an exhibition in Nagasaki during the first week of Dec.

For the most part this firing went well, aside from the fact that I exploded my large platter. Drat.