Pontificating on the joys of kiln bisquits
Author: KaratsuPots
Trim the fat…
The first time I saw Rokujizo (this teabowl), I didn’t think much of it as I flipped through the pages of the pottery magazine. A decade or more later, this is bar none my favorite Ido teabowl. The shape, color, and landscape are amazing, but more than that, looking at this bowl got me thinking about economy in throwing and trimming more than any other piece I can think of.
If you look carefully at the foot, you’ll notice that it is untrimmed. The width and height of the foot, the thickness of the base, and the angle from foot to body were all decided on the wheel as a decision on the part of the potter to make a form which wouldn’t require much attention after throwing.
When you think about it, trimming and reprocessing scraps takes much more time than throwing. If that step can be abbreviated or eliminated, then you’ve saved a lot of time and sweat.
My sakazuki shown here are inspired by this economy of process shown in Rokujizo, as well as a type of sakazuki called ‘yama-sakazuki’ which are entirely trimmed. They are very quickly made utilitarian cups which were used for large groups and artistic value was not a consideration. They are easily identifiable by their untrimmed feet, both outside and in. The foot is just a flat surface with string mark from the cutoff string. These kind of cups often have a wobble from an uneven cutoff.
These sakazuki had just the inside of the feet trimmed, as many customers today like the look and feel of untrimmed cups, but the wobble not so much… it also gives me a place to sign the cup without marring the untrimmed outer surface.
There was very little trimming scrap upon finishing, and it was still soft enough to wedge back into the remaining unused clay, so no clay recycling!
Pigment:Glaze Notes
Yesterday’s firing was my first gas firing of this glaze, body, and pigment, and first ever primarily porcelain firing.
This piece’s specs:
Porc:Sandstone body 6:4
Taishu:Ash glaze 7:3 @ 40°
Gosu:Oni-ita pigment 6:4 (7:3)?
Orton cone 7.5 light reduction
Pigment blacker than expected, too thick or maybe not enough reduction?
Body is not vitrified completely at this temp, but pure Izumiyama probably would be. Good for teaware and tableware, but for restaurant use should probably be fired higher.
Cup Nomenclature
This morning I read a very nice article about Japanese cups, defining their names and uses. You can see it here:
https://www.veniceclayartists.com/japanese-tea-cups-yunomi-and-guinomi/
It is quite informative (it even mentions Karatsu) and even better, has some really stunning contemporary pieces to
see (but no Karatsu, tsk, tsk, more on this below).
There is one point in the article I would like to clarify a bit: the author mentions the word hakuji , meaning white porcelain made from kaolin clay from Izumiyama. For most folks this is probably a sufficient description, but at Karatsupots blog we are deep into ceramigeek territory, so consider yourself duly warned.
Izumiyama was the first deposit of porcelain stone discovered in Japan, in 1616, in present day Arita. Old Arita, Imari ware was made from this material. However, another porcelain deposit was discovered in Amakusa, Kumamoto, in the late 1600s, and began to be used for porcelain production in the early 18th century. Today, Amakusa stone accounts for more than 80% of porcelain in Japan. It is whiter than Izumiyama porcelain stone, is easier to work with, and much cheaper. Very few artists today work with Izumiyama porcelain (and probably no factories, but this is speculation on my part). Izumiyama is not being mined currently.
Izumiyama is still available, but not very dependably, and it is quite expensive. I use it because it is absolutely beautiful in wood firings, but is is difficult to work with and losses are high. Ok, enough on Izumiyama.
Next, guinomi, choko, and sakazuki. All are names for sake cups, with one caveat: guinomi are not just for sake, while choko and sakazuki are.
Now, to rectify the lack of Karatsu ware pictures. Again, for most folks it is not all that important, but this is Karatsupots after all, and to quote Pink Floyd’s The Trial, “this will not do.” So, here are some pictures of Karatsu cups.
In the hot seat
A couple of days ago I sat down with my newly acquired kickwheel to see what I could do. I’ve used my homemade kickwheel frequently for handbuilding and paddle work, not as much for throwing, because it is quite tall and the flywheel is quite high from the floor.
The new kickwheel is craftsman made, and shorter, making it easier to use without a special seat. In the two days of throwing, I discovered two things: 1. my homemade wheel spins better making it great for coil and paddle work, and 2. The new kickwheel is easier to throw on because the fly wheel is so much closer to the ground.
I decided to throw with a difficult body to keep things interesting. Stamped Izumiyama porcelain stone that had been levigated and filter pressed, with the removed large particle material re-added as 30% of the body. This makes for a pretty short body but it does have more backbone than straight filtered Izumiyama. I started with small, simple shapes for the first day, and moved to larger bowls on the second, sort of a cross between an Ido form and a wider more open shape typified in a lot of Ri period Korean work.
My goal was to keep things as light as possible off the wheel, and requiring as little trimming as possible.
I waited a bit too long with the small cups, but they trimmed with some very nice texture even though a few had some of that soft porcelain tear-out. Since they are sake ware, I’m hoping this will add to their landscape in the firing.
Very happy overall with the texture of the interior of the feet. When I first discovered that porcelain would trim like this, it was a major discovery for me, and prompted me to start working with it.
Clay clay clay
When I was polishing work from the fall firing yesterday, I noticed two pieces that had been glazed, fired (on shells)glazed again, and fired again (on shells). This isn’t too unusual, but in the case of these two pieces, they were literally fired side by side both times and had the same glazes applied, twice.
The only difference between the pieces is the clay body. The teabowl is clay/sandstone 50/50, and the smaller cup is clay/sandstone 10/90.
Now probably it shouldn’t, but the difference in the fired glaze surface astounds me. And all other things being equal, it must be that 40% difference in clay content that has changed that glaze.
Since the glaze is collected, I don’t have an analysis, but my guess is that the higher alumina content in the higher clay body is responsible for making that high silica glaze go clear, by adding alumina to the glaze matrix and fluxing more of the silica.
