Friday, 13 March 2009

The Principles of Shino

Over the past few weeks I have been asked by several potter friends about the materials for Japanese shino glazes and their equivalents in the west. I haven't actually used a shino glaze for about fifteen years, but with some of the restaurant collaborations and requests from chefs, I may soon be revisiting the shino arena.

It is probably useful to firstly put shino into a frame of reference.

Once upon a time there was a tea master named Shino Soushin (1444-1523) who directed that the potters of Mino produce a white glaze. Their solution was to coat a low iron clay, either mogusa clay or gotomaki clay, with a local feldspar, occasionally mixed with some clay to make it more user friendly. The resulting glaze, wood fired of course, tended to be slightly grey in oxidation (Nezumi Shino meaning Mouse Shino) or pearly white with red flashing in reduction.
Generally Shino glaze is accredited to the Momoyama period (1568-1600), and, yes, some of the finest shino glazes come from that period, but it had its roots in the Muromachi period (1336-1573). Interesting to note the overlap.

So...what was the feldspar?!

The simple answer is Hiratsu Shino Choseki. Choseki is Feldspar, the Kanji "長石" means "long rock" referring to the rhombic crystalline structure of feldspar. This feldspar has a high Alumina to Silica ratio, combined with fairly high Sodium/Potassium content. It is in fact the Sodium and Alumina under reduction that give the distinctive soft pink and orange flashing of Shino. Which is why Nepheline Syenite lends itself so well to shino style glazes. Compare the analyses;

Hiratsu Shino Choseki ;

SiO2 65.4
Al2O3 20.5
Fe2O3 0.09
TiO2 0.01
CaO 0.14
MgO 0.03
K2O 6.89
Na2O 5.13
Ignition loss 1.59

Nepheline Syenite;

SiO2 60.1
Al2O3 23
Fe2O3 0.09
TiO2 0.02
CaO 0.37
MgO 0.02
K2O 4.75
Na2O 10.6
Ignition loss 0.47

Many recipes have been based on this material, especially with its high sodium content. With the addition of up to 40% Clay (Ball clay, Kaolin, Porcelain, Terracotta or Fire clay) a huge range of variations can be achieved.

The representative Ball clays added to the feldspar in Japan were either Gairome;

SiO2 49.72
Al2O3 34.55
Fe2O3 1.23
CaO 0.16
MgO 0.24
K2O 0.74
Ignition loss 12.8

Or Kibushi Nendo;

SiO2 48.56
Al2O3 33.48
Fe2O3 0.87
CaO 0.30
MgO 0.15
K2O 0.36
Na2O 0.63
TiO2 0.12
Ignition loss 15.76

Other recipes have taken note of the high alumina to silica and high Alkaline flux and have included Soda ash into the mix. Others depend on fluxes other than Soda, the most significant being Lithium. In the west many Shino glazes use Spodumene as the base, which is basically;

Li2O. Al2O3. 4SiO2

This is as rare as hens teeth in Japan, and the best replacement is Petalite;

Li2O. Al2O3. 8SiO2

Of course the Silica present in the rest of the glaze needs to be reduced to compensate. This can sometimes be done by replacing Kaolin for Ball Clay, but it is important to test with the materials one has at hand, as there are huge regional variations. Alternatively an addition of Lithium Carbonate and Alumina will compensate, but you will need to do the math!

It is this high alumina, high alkaline flux that gives my pottery its distinctive peach blush, as I am using a porcelaineous, high alumina, low iron, clay in a wood firing, from which the natural salts vaporise from the wood, with the addition of a small amount of soda ash at the end of the firing. Not Shino, but based on the same principles.

There are books that purport to tell the secrets of Japanese wood firing, with lists of "American" shino recipes and no examples of any actual representative Japanese ceramics whatsoever. OK, I can live with that. As recipes they stay within the parameters of the original Hiratsu Shino style, and if you are satisfied with that, fine.

But that is NOT all, oh no that is not ALL!

Japanese shino glazes are not all made with Hiratsu Shino Choseki, and not all flashing is Soda/Alumina. One must not forget our old friend Iron, who so happily serves the potter with a huge gamut of glaze effects.

"And so", said the Cat in the Hat, "So, so, so, I will show you another good trick that I know!"

As my sempai Ken Matsuzaki demonstrates so well, any feldspar can make a Shino, given the presence of Iron either underneath the glaze or within range of the external glaze surface. It is the nature of Iron oxide that in a heavy reduction atmosphere, between the temperatures of 1090 and 1130, over an extended period of time, it will volatise and migrate to the surface of the glaze. This must be done before the glaze cinters, sealing it and preventing the Iron from seeping through the porous glaze matrix. By painting a decoration in Iron under the glaze, or by utilizing a small amount of Iron in or on the body beneath the glaze an Iron blush can be created on the opalescent white feldspathic glaze. A wash of Iron inside a saggar surrounding the work can give a similar effect.

Maintaining a heavy reduction during cooling is essential, but in the end the micro fine layer of Iron will re oxidize to give the distinctive Shino blush. Merely seeing Iron through a semi transparent glaze is not Shino. There is a lustre and warmth that springs from the natural process which makes shino special. Colours that resonate with sunrises and sunsets, that remind us of the soft warmth of human skin.

The Japanese traditional teaching system does not put the onus on the teacher to teach; It is the responsibility of the student to actively learn. Shimaoka sensei told me that there are no secrets. You just need to ask the right questions.

23 comments:

  1. Excellent post, very informative! That is definitely going in the “things to remember for the future” file. I especially liked the bit about the traditional Japanese teaching system. The students should be responsible for their own education, at least to some degree. As a teacher in the mid-west U.S.A. I can tell you that is not how things work over here. The students (and unfortunately the parents, administration, politicians, etc) seem to think that the teachers are the only ones responsible for education. The teachers/schools are the first ones blamed if students are not learning like they should. Many are losing funding or even facing being fired or shut down because no one want to hold students responsible for their own education. Again, great post. Keep up the good work and happy potting!

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  2. Brilliant post!!! Thank you so much!!
    ~Craig Edwards

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  3. Thank you Rob and Craig,
    I'm glad the info is useful. It is sometimes hard to get reliable info on techniques and Materials, so I just wanted to share what I have.
    Actively learning is very important, but it's also important to pass on the things that we learn.
    Cheers,
    Euan

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  4. Thanks Euan. I listed this at my Facebook page. You should get on Facebook.

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  5. Here is a link to a shino bowl of mine which shows two kinds of iron color. The surface red and then the brown from iron decoration on the bisque: http://shinoglaze.blogspot.com/2006/10/first-mogusa-clay-and-e-shino_08.html

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  6. Extremely interesting post, thanks. I'm just starting to experiment with shinos, reducing them in a saggar using an electric kiln.
    I'll try the wash of iron on the saggar walls as you mentioned.

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  7. Euan! You're still the best potter I've ever met and seeing your work here in 'blog world' is inspiring. Am soon to get myself a gas kiln--not able to have a wood firing kiln in suburbia...--and shall soon be potting in my own studio here in Dapto. Would love to see you and Mika and the kids again soon so do let us know when you're back in Oz for a visit. Am also taking a course at TAFE in Sydney to have access to a kiln for now; have been using their Shino and so far, its been giving me all sorts of ideas. All I must do now is produce and see what the Shino tells me to do;) Renee

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  8. Great post.
    Living remotely and having little formal ceramic eduction but an abundance of wonderful local materials in bauxite and kaolin led to my dabbling in a shino using the local kaolin over bauxite with amazing results in my gas kiln. Self education is a wonderful teacher and my love of shino has not diminished. It is so representative of my environment. All my glazes contain the local kaolin so it seems in my ignorance I chanced upon the common thread of success with my 'Weipa' shino.

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  9. Mr. Craig,

    I am a devotee of the Japanese Shino, and have done my best to re-create it with American materials and processes (ie: gas-fired kilns). I found your article on Hiratsu Shino Choseki very interesting. I had actually already come discover, through glaze experiments, a mesh that had a very similar chemical formula to Hiratsu. Your article helped me, however, to refine my formula. By the way that meshed spar is 70% Custer Feldspar (a high potassium feldspar - as far as I know any high potassium spar will work) and 30% Nepheline Syenite. These proportions can be adjusted up or down to taste. More custer = better texture/ less orange flashing (and from what I'm reading from Lee Love, mor pink flashing). More Neph sye will yield the opposite (more fluxing, less texture, and more orange flashing). Anyway, thank you very much. Your article was very encouraging and of great help. However, today I was reading back over it and I was caught by the section regarding fire color. You wrote that it is important to retain a reducing atmosphere during the cooling cycle, and gave a specific temperature range during which reduction must be executed to volatalize the iron. I have a few questions. Can the reduction cycle begin as late as 1090 C (which i believe we call Cone 05 or 04 - don't know if you use them or not)? Does the initial reduction period need to come in the form of a reducing soak, or can you maintain a regular climb in temperature? Furthermore, I have heard from multiple sources that a period of re-oxidization is essential for good fire color. some suggest it at the peak of the firing in the form of a long soak. Others suggest it as a soaking period during the cooling cycle. Do you find any validity in this? Is there any sort of long soaking period at the peak of the firing (either reducing or oxidizing), and do you ever have to intentionally re-oxidize or does it happen naturally? My last question is this: from whatever temperature you begin reduction, do you maintain the reduction all the way until the peak of the firing, or is that unnessecary?

    Any answers or advice are GREATLY appreciated. I am still largely baffled by Shinos as the American knowledge of this glaze is remarkably insufficient. I have, however, had some success with surface textures (pinholes, and fissures) at a low Cone 9 (anywhere from 1220-1280 C, depending on firing speed). Unfortunately, early reductions by my professor and overfiring have killed many of my shinos by essentially boiling them. And getting that fine, subtle fire color still greatly eludes me.

    Thank you very much for your time.

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  10. Firstly, thanks for the custer feldspar hint, if it is OK I'll put that on a follow blog entry for US potters to reference. Custer is as rare here as Hiratsu is there, so I won't be able to use it unless i'm doing a workshop stateside(you never know).
    Now,firing schedules. As I said in my blog, I don't use shino now, but the flashing principle on the porcelaineous bpdy is the same as the Hiratsu theory; soda/alumina heavy reduction flashing. For this a steady reduced climb, reduction soak at top temp which for me is 1300, Seger cone 10, orton cone 11 I think. I then crash cool to 1100 by just not stoking anymore, which takes about 30 minutes, and by the end of that it is starting to oxidize. I then stoke a bout 7kg of wood into the front of each firebox and close it up tight. Haven't measured how long it reduces for or down to what temp, generally I just go to bed.


    The Iron Flashing is different. I don't currently use this because there is no iron in my body. Iron will volatise and migrate to the surface of the uncintered glaze between 1090 and 1130. A long heavy soak then is necessary between those temperatures, going up and down between them is fine, but lower than that it doesn't volatise, higher than that the glaze cinters and the iron can't get through so you've missed your chance. My sempai who specializes in shino soaks for a disgusting length of time (days!) but gets great results. A couple of hours should give some good results. then fire as normal for the soda flashing. Iron oxide painted on the inside of saggars will flash the glaze also, even above the cinter temp because it is already outside the glaze. A long reduction soak at 1250 is good. Reoxidation is only necessary for iron fire colour, not soda, but yes, no more than half an hour of clean oxidation at the end will brighten up flashing and clear otherwise murky glazes.


    Hope this helps, all the best,
    Euan

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  11. Euan,


    Wanted you to know that I did a firing based on your advice, and it came out beautifully. A normally un-impressive shino we had in the studio developed some of the most beautiful blushing I have ever seen in person. We reduced at Orton Cone 08 , and then did a short soak between 1090 and 1130 - then we soaked in reduction at Cone 8, finally ending the firing by oxidizing to cone 9. It was fantastic. I can't wait to try it with my shino. Thank you so much.

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  12. Euan,


    New firing a vastly improved schedule. Still based on your long reduction. We fired to cone 04 (meant to go to Cone 08, but kiln got away from us), and then reduced. We then slowed down the climb greatly (maybe 1 degree per minute, probably less), until maybe around cone 1, then let it climb normally to Cone 9 (weak 9). We then did a slow controlled cooling in oxidation down to 1800 deg. F and soaked there for awhile ( i think a few hours) and then closed her up. Euan, I got pink shinoes. On some of the pots I brushed a thick iron/redart (iron-bearing clay) slurry, and then glazed over the paintings. After firing, the areas with the paste turned a gorgeous purple (think the murasaki shinoes of Tomio Suzuki). This was the best firing i have ever seen.

    PS: my shino has a lot of potassium feldspar in it.

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  13. Euan, I come to this well after you have posted it, but want to thank you for sharing your knowledge and experience. Thank you, thank you!

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  14. Thank you for sharing this

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  15. It's really amazing to combine Japanese cuisine and skills in interior design. Highly appreciated . Job Well Done. Thank You so much.

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  16. Mr. Craig,

    I am new to the “Shino realm” and have a few questions. I want to make a authintic Japanese Shino glaze, but I only have an reduction electric kiln. What I’m getting from you is, that I can’t do Shino with an electric kiln; can I? I am a little confused about what’s a “fake shino”; can I make a glaze using felspar and silica, as the sole base, and call it “Shino”? I am working with a high-iron clay body. Appreciate this great read of yours. Looked for hours trying to find out about shino ; this help clear up a lot! Blessings, Kilian

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  17. Mr. Craig,

    2# P.S. - I have an oxidation, electric kiln.

    I am new to the “Shino realm” and have a few questions. I want to make a authintic Japanese Shino glaze, but I only have an oxidation electric kiln. What I’m getting as I read this is, I can’t do Shino with an electric kiln; can I? I am a little confused about what’s a “fake shino”; can I make a glaze using as felspar and silica the sole base and call it “Shino”? I am working with a high-iron clay body. Appreciate this great read of yours help clear up a lot! Blessings, Kilian

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  19. I have a new buncheong Ido bowl from my recent time in Mungyeong, S. Korea. It does not have a vitrified body either. The firer their long noborigama in 17 hours.

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  20. See the video at the top of the page (I flick the bowl to try and ring it.)

    https://www.facebook.com/ikiru.kiln

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  22. I worked with John Dix in his ogami studio outside Sasayama for two months last Fall, and got lovely pink shinos using a Fukushima feldspar(High P) and kaolin base(80/20) to which I added some low Melt Spodumene I brought from my studio in Eugene, OR. At 12% added Low Melt we got some lovely pinks on the clays from Tajimi and a five day firing in John's anagama. Wish I could post pics here, but email me to see them.

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    Replies
    1. Hank, post them on Facebook and share the link here. Thanks!

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