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alexanderwilds

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  1. Within Nigel Wood's "Chinese Glazes" is a quote from Shoji Hamada, "My recipes are simple, my materials are complex." Western glazes recipes tend to be long and exacting - 12% this, 1.7% that - and so forth. Oriental glazes tend to be really simple, for example, a classic Korean celadon is, by weight, 3 parts porcelain clay to 2 parts washed wood ash (the 1% iron content is in the clay body). Sounds easy enough. It is not so simple. The chemical composition of every natural clay is a very complex mix of silica/alumina/feldspar and a dozen other oxides, and wood ash chemistry varies widely by not only species - pine ash is quite different from oak - but by locality, and by bark, leaf, and trunk. The differences between various regional wares often has less to do with design aesthetics and processes, and more to do with local materials; it is what works using what they have. While American potters are often proprietorial about glaze recipes, Japanese almost never are; they are happy to explain exactly how they do things, because you really cannot copy them - your clays, your glaze materials, your kiln, etc., are not the same. Western potters know what they want in a glaze, and are disappointed if they don't get exactly what they had in mind. Koreans and Japanese use simple, reliable recipes, and appreciate and both potters and buyers accept variations due to the impurities of the materials. Western artists often know more technically, and make technically better glazes. Asian glazes are more interesting, for the content are often a mystery even to the makers.
  2. Percentage Of Water To Glaze Ingredients Is ?

    Here in Japan the "test tiles" (actually sake cups) usually have samples of the glaze in question at various viscosities. The differences for the same glaze can be startling, particularly regarding how the glaze interacts with the underlying clay body. For example, a transparent feldspar/ash over a lightly iron bearing clay will be like green/gray celadon when thicker, and baby pink when thin (see Hagi ware). So I guess it is not a question of what is "correct", but rather a question of what effect you want.
  3. Clear Glaze Crazing

    Crazing occurs in the final cooling phase - under 300 degrees celsius. It is the glaze contracting more than the body. So beyond the glaze recipe consider: 1. clay body compatibility 2. Insulation, such as blanket the kiln to slow down cooling particularly at the final stages.
  4. Firing An Accidentally Glazed Green Ware Pot?

    Glaze on green ware? There is a thousands-years-long tradition, particularly in Korea and China. "Raw glazing" they call it, and they do it all the time. From sad personal experience, I have two suggestions: 1. clay based glazes, rather than feldspar based, work much better, particularly if the body clay and the glaze clay are the same material. Clay is stickier, and will shrink/expand with the body. Feldspar glazes tend to fall off, flux into the body, or crawl. 2. Timing is important - apply glaze when leather hard, not wet (it melts to body) or bone dry (it cracks).
  5. Shinos

    I spent some time today with some Japanese potters who focus on shino in their work, checking on the above comments from yesterday, and have corrections and further info regarding Japanese Shino glazes. 1. Glaze is mostly, like 95%+, feldspar, usually "Kamado" feldspar, a sort that melts to a viscous, semi-opaque, milky white. Some clay is added, either kaolin, diatomacious earth, porcelain, or clay from the body of the vessel, as explained further below. I add that the Japanese potters got into a serious debate regarding what they liked to add and how much, but it obviously is a matter of experimentation and desired effect. 2. The idea is to match the melting point of the glaze to the firing temperature, so that the Shino glaze just barely melts, maybe (thus the 10-day-long firing schedule). The more clay you add, the higher the melting point, the more matt the surface, and, due to the increased shrinkage, the more cracks in the glaze. The more clay you add, the sharper the edges of the cracks. 3. To promote pinholes, the surface of the green ware is scraped while leather hard, roughening the surface. This gives a solid mechanical bond to the glaze, and promotes the release of gases from the clay through the glaze, leading to pinholes and blossoms of colors from the clay body. 4. To promoting crackling the surface, and to keep the glaze white, the green ware is burnished, allowing the glaze to slip, and maybe fall off, the surface. Obviously, these glaze "flaws" are what the Japanese potters are after - a feature rather than a bug. I hope that helps. Alex Wilds
  6. Shinos

    I am in Japan, teaching traditional Japanese ceramics. More accurately, I am learning about them all the time and passing off my new knowledge as old wisdom. I see a lot of great shino glazes, and ask how they are done. Here is what the folks around here say: 1. straight feldspar, with a binding goop ("nori") of wakame seaweed (and thus the salt) to help stick it to the pot. However, many just use a rice based "nori" that comes in a tube for gluing paper. 2. Iron rich clay. It is not a red, terra cotta sort of clay, rather, a a rough yellow stoneware clay, probably with trace cadmium as well. 3. a ten day firing - five up and five down - to 1230 degrees celsius (cone 6). Although 90% of kilns around here are fired with kerosene, the shino folks use gas, presumably because it is easy to maintain the slow firing rate and atmosphere. I would hate to see the bills. Just getting a white shino like the sugar glaze on a Krispy Kreme doughnut can be pretty quick - a day or so at most. But for the rich, red/orange variations to happen, well, it takes days for the iron and other minerals in the clay body to migrate to the surface and blossom, thus the long firing schedule. Alex Wilds Kofu, Japan
  7. How To Start Making My Own Wood Ash Glaze

    I have been in Japan for many years working with ash glazes. Most Japanese clear glazes are simply wood ash and feldspar, which are locally dug and known only by that location's name; there is not a great variety in their effects. In the local ceramics supply store there are test tiles that (A) range from pure feldspar to pure wood ash, generally 10% difference (so 9:1, 8:2, 7:3). The type of ash matters more than the feldspar, however all seem to work well. In Mino and Seto the ash of chestnut bark is held in high regard, and in Oita Prefecture Oak ash is particularly esteemed. My own experience is that (A) the ash/feldspar balance has mostly to do with the temperature to which one plans to fire, and ( the atmosphere, firing schedule, and interaction with the clay body have much more effect upon the outcome than type of ash, feldspar, and balance of the two. I was in Hagi recently, and spoke at length with Takeshi Kaneko, a highly respected potter. In Hagi ware, the glaze is usually 50/50 ash and feldspar (by weight). He uses the ash of the autumn leaves, generally Japanese chestnut, but only because they are plentiful and he needs to burn them anyway. Although most Japanese fire glazes to 1230 degrees celsius, Hagi ware is fired to only 1200 degrees in a slightly reducing atmosphere, five hours up, five hours down. If over-fired all of the beautiful effects ("gohonde") is lost, making boring surfaces. The 50% ash content is required to flux the glaze to mature at the lower temperature. In wood-fired kilns that seek a natural ash glaze from the firing itself, red pine is the primary fuel, but this because it burns hot and fast; they tend to finish off the firing with hard woods such as oak or elm for effects. The process means that most of the ash in the ash pit is from pine, and so much of the mixed-and-applied ash glazes tend to have a lot of pine ash in them. Alex Wilds, Kofu, Japan
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