Archive for January, 2015

  • Underglaze

    Qinghua Stone

    Pictured above is a type of stone (叫珠子) mined in Zhejiang province and sold in Jingdezhen.  It is primarily used for making Chinese underglaze blue & white (qinghua).  These hard nuggets are quite expensive, while the softer stone surrounding these nuggets is about six times cheaper.

    In the magnified view you can see that this stone is a composite of many different minerals.  I am not an expert but there are definitely chunks of silica and mica.  From tests, it seems that the darker bits are primarily iron and manganese.  In ancient times I assume that this stone also contained a small amount of cobalt, however from my tests that no longer seems to be the case.  The proprietor of the materials shop confirmed this, although he mentioned that ores containing cobalt are still sometimes unearthed and fetch a premium price.

    In Science and Civilisation in China: Volume 5, Chemistry and Chemical Technology, Part 12, Ceramic Technology, Part 6, Pigments, Enamels, and Gilding (pages 680-692), Nigel Wood writes extensively about the composition of Chinese blue & white underglaze pigments, with analyses of cobalt bearing absolites and other ores.  Nigel Wood also covers the subject in Chinese Glazes (pages 61-66).

    For me, the basic lessons to be learned from Wood’s research are: a) that underglaze blue pigment composition varied substantially throughout history and between kilns (especially between the official and folk kilns), b) the importance of the ratio between the primary coloring oxides (cobalt, iron, and manganese), and c) the influence of other oxides (especially silica and alumina) present in the underglaze pigment and covering glaze upon the final color.

    Qinghua stone 100%

    Qinghua stone 90% Cobalt Oxide 10%

    Qinghua stone 80% Cobalt Oxide 20%

    Above is pictured a quick first test of the qinghua stone.   An underglaze was made by crushing the rock and sieving it through an 80 mesh screen.  From left to right:  100% ore, 90% ore/10% CoO, 80% ore/20%CoO.  As you can see from the 100% test it appears that the ore contains little or no cobalt.  This is obviously a poor first test, as underglaze blue & white is usually ground very finely.

    Below is a more refined test.  The qinghua stone was first bisqued to 900 degrees, crushed, and sieved through a 100 mesh screen.  Finally, the stone and cobalt were ground with a mortar and pestle.  In my opinion, the combination of Cobalt, Iron, and Manganese result in a much more interesting range of colors than Cobalt used alone.

    Qinghua stone 95% Cobalt Oxide 5%

    Qinghua stone 90% Cobalt Oxide 10%

    Qinghua stone 85% Cobalt Oxide 15%

    Qinghua stone 80% Cobalt Oxide 20%

    Qinghua stone 70% Cobalt Oxide 30%

  • Glazes

    Blue Celadon Glazes

    All of the following Blue Celadon recipes and more can now be found on my new open-source ceramics recipes website, Glazy:  http://glazy.org/search?category=36&subcategory=41

    Complete Guide to High-Fire Glazes

    These are tests of some of the Blue Celadon Recipes found in High Fire Glazes.  Tests fired in multiple kilns in temperatures ranging from 1300-1310 Celsius reduction.

    Craig Martell Blue Celadon

    Custer Feldspar:  61.7

    Silica: 21.2

    Barium Carbonate: 4.5

    Wollastonite: 12.7

    Black Iron Oxide: 1

    Pete Pinnell Blue Celadon

    Custer Feldspar:  24.5

    Silica: 34.3

    Whiting: 19.6

    Kaolin (Grolleg): 19.6

    Barium Carbonate: 1.9

    Tin Oxide: 1

    Yellow Iron Oxide: 0.5

    Sam's Satin

    Custer Feldspar:  40

    Silica: 34.5

    Whiting: 15.5

    Barium Carbonate: 4

    Dolomite: 6

    Yellow Iron Oxide: 0.5

    Cliff Lee Blue Celadon

    Custer Feldspar:  50.5

    Silica: 24.9

    Whiting: 17.2

    Kaolin (Grolleg): 3.7

    Dolomite: 2.6

    Zinc Oxide: 1.1

    Red Iron Oxide: 0.75

    Choy Blue

    Custer Feldspar:  50

    Silica: 28

    Whiting: 6

    Kaolin (Grolleg): 4

    Barium Carbonate: 12

    Red Iron Oxide: 2

    Ishii Blue Celadon

    Custer Feldspar:  49

    Silica: 31

    Whiting: 20

    Black Iron Oxide: 1

    Celadon Blues

    Robert Tichane’s Celadon Blues focuses primarily on Chun (Jun) glaze, but also covers Qingbai, Longquan, and other ancient Chinese glazes.  While perhaps not as informed as Nigel Wood’s Chinese Glazes, Tichane approaches the subject from the perspective of a glaze chemist and gains valuable insight into the nature of blue celadons.  Through testing, Tichane arrives at two formulas.  The “532.1” formula contains 50 parts feldspar, 30 parts silica, 20 parts limestone, and 1 part iron oxide.  The “5321.1” formula is the same but adds 10 parts kaolin.  The type of kaolin added greatly affects the color of the glaze, for blue celadons a kaolin very low in titania such as Grolleg or New Zealand Halloysite is required.

    Below on the left is Tichane’s 532.1 formula with 1% yellow iron oxide (YIO).  On the right is the same formula but with Wollastonite instead of Whiting (of course this adds some silica to the mix).  These tests were fired in a public kiln, temperature is uncertain but at least Orton cone 12, I believe Tichane’s tests were fired to cone 10.

    Porcelain, Orton Cone 12 Reduction

    Porcelain, Orton Cone 12 Reduction

    It is quite simple to create a blue celadon suited to your particular firing style using Tichane’s methods and triaxial blends.  From a triaxial blend of potash feldspar, silica, and whiting I arrived at a recipe suitable for Orton cone 11-12 reduction firings:  56 feldspar, 30 silica, 14 whiting plus .6-.8 yellow iron oxide.  Some variants of this glaze are shown below.  All tests fired to approximately Orton cone 12 in heavy reduction.

    .6 YIO

    .6 YIO +2 BaCO3

    .6 YIO +2 BaCO3 +1 SnO2

    .8 YIO +2 BaCO3 +1 SnO2

    .8 YIO +2 BaCO3 +1 SnO2 +2.5 Dolomite

    Formulating Your Own Celadon

    Personally, I really like the Pinnell Blue Celadon recipe in John Britt’s book.  It’s a very beautiful, smooth and “natural-looking” blue celadon.  However, I’ve found that the glaze is difficult to apply given the large amount of Kaolin in the recipe.  A few months ago I fired about 20 pieces with Pinnell celadon with beautiful results except that the glaze crawled on every single pot.  I still haven’t determined if the problem was due to a) glaze application (sprayed inside, dried, then sprayed outside), b) ball milling the glaze for too long (3 1/2 hours), or c) too much shrinkage of the glaze due to the kaolin (using New Zealand Halloysite).

    And although no-kaolin recipes like Tichane’s 532.1 and Craig Martell’s blue celadon almost always fire a nice blue, they seem a little artificial to my tastes, perhaps a little too colorful.  It’s also because this type of Wollastonite-based celadon is covering a lot of Jingdezhen ware these days, and I’m tired of seeing it.  Finally, these glazes tend to sink to the bottom of glaze buckets and solidify there due to lack of clay.

    So I decided to do a simple triaxial, based in part on Tichane’s 5321.1 recipe.  I still want kaolin in the recipe, but not as much as in Pinnell blue celadon, so I picked an amount halfway in-between the two, 10%.  (Again, I’m using New Zealand Halloysite.  Grolleg is also suitable.)  I also decided to add 3% dolomite- based on Nigel Wood’s Chinese Glazes and past experience I know that a little magnesium combined with the calcium can give the surface a slightly waxy feel.  With 13% of the recipe taken up by kaolin and dolomite, I have to adjust 87% Potash Feldspar, Silica, and Wollastonite.  (You could use Whiting of course, although it out-gasses more than Wollastonite.)  Finally, I’m not adding any Barium Carbonate.  (If you want a rich blue celadon you can try adding 2-4% Barium Carbonate.)

    All these tests are the same porcelain body fired together in a heavy reduction atmosphere to Orton cone 10 1/2.

    I realize it’s really difficult to see the differences between glazes in such a small photo.  Furthermore, some tests look richer, but it’s partly due to small changes in camera exposure and glaze thickness rather than glaze composition.  I prefer the diagonal lines going down with Wollastonite at 20-22 percent.  I should have added another couple rows to the bottom of the triaxial, because I prefer the glazes more as the silica increases.  (I thought there was already too much silica in the glaze, including silica contributed by the wollastonite, so I stopped early.)

    Below is a bigger photo of one of the tiles.  It’s almost like some Longquan glazes I have seen.  I think this particular glaze would look great over carving or molded/sculpted work, and it might really look good on stoneware or dirty porcelain.  I’ll post pictures once I try it out.

    I’ve posted the recipe on Glazy:  http://glazy.org/recipes/3189

    Adjusting Pete Pinnell's Blue Celadon

    Years ago I tested Pete Pinnell’s Blue Celadon recipe and loved it, so much so that I didn’t even think of bothering to adjust the original recipe to suit my materials.  But this last kiln I wanted to try swapping out Whiting for Wollastonite, and I thought I might as well adjust for New Zealand Halloysite instead of Grolleg.

    Below is a small triaxial of Pinnell’s Blue Celadon adjusted for New Zealand Halloysite.  The top of the triaxial is the closest verison to the original.

    Using Halloysite instead of Grolleg wasn’t a huge change, and I couldn’t see much of a difference from the original recipe.  The bottom of the triaxial is somewhat interesting- color improves as silica replaces halloysite.  This is a similar finding as with Tichane.

    Replacing Whiting with Wollastonite

    Next is Pinnell’s Blue Celadon with New Zealand Halloysite instead of Grolleg, and Wollastonite instead of Whiting.

    The recipe at the top of the triaxial most closely matches the original recipe.  As with the previous triaxial, color is better on the right side where silica is greatest.

    As with many wollastonite-based celadon glazes, this glaze has a very fine network of bubbles that are smaller and more evenly sized than those in the whiting recipe.

    It is difficult to see in the photograph, but the color is also better in the wollastonite version.  I believe this is due in part to the fact that much of the silica is introduced with the wollastonite.

     

     

    My favorite glaze is the Halloysite/Wollastonite recipe at the top of this triaxial (which is closest to the original recipe).  You can find it on Glazy: http://glazy.org/recipes/4571

    However, I also like the glaze on the right of the second row.  I wish I’d done a test to the right of the top glaze, in other words Potash 30.5, NZ Kaolin 18.5, Silica 24.

    Pinnell's Blue Celadon with Halloysite and Wollastonite.

  • Glazes

    Blue Glazes

    All of the following Blue glaze recipes and more can now be found on my new open-source ceramics recipes website, Glazy:  http://glazy.org/search?category=36&subcategory=65

    The following tests were fired in two Jingdezhen public kilns at approximately cone 12 and in my own kiln at cone 10.  I just wanted to get a general idea of the blue glazes listed in High Fire Glazes.

    Market Blue

    Custer Feldspar 50, Whiting 4, Kaolin 24, Dolomite 22, Cobalt Carbonate 0.5

    Market Blue, Cone 10 Reduction on Porcelain

    Market Blue, Cone 10 Reduction on Stoneware

    Market Blue, Cone 12 Reduction on Porcelain

    Royal Blue

    Custer Feldspar 27.3, Whiting 23.3, Silica 27.3, Kaolin 19.2, Zinc Oxide 3, Cobalt Carbonate 5

    Royal Blue, Cone 10 on Porcelain

    Royal Blue, Cone 10 on Stoneware

    Royal Blue, Cone 12 on Porcelain

    Royal Blue, Cone 12 on Porcelain

    Satin Sky

    Satin Sky, Reduction cone 10 on Porcelain

    Satin Sky, Reduction cone 10 on Stoneware

    Satin Sky, Reduction cone 12 on Porcelain

    Satin Sky, Reduction cone 12 on Porcelain

    Winn Blue

    Winn Blue, Reduction cone 10 on Porcelain

    Winn Blue, Reduction cone 10 on Stoneware

    Winn Blue, Reduction cone 12 on Porcelain

    Winn Blue, Reduction cone 12 on Porcelain

    Blue 1

    Blue 1, Reduction cone 10 on Porcelain

    Blue 1, Reduction cone 10 on Stoneware

    Blue 1, Reduction cone 12 on Porcelain

    Blue 1, Reduction cone 12 on Porcelain

    Dark Water Blue

    This recipe calls for 2% additional Iron Chromate, which I don’t have.  I tried this glaze without the Iron Chromate, as well as substituting Iron Chromate for a combination of Red Iron Oxide and Chrome Oxide.  I don’t know what this glaze is supposed to look like..

    Dark Water Blue, Reduction cone 10 on Porcelain. Sub 2 Iron Chromate for 1 Red Iron Oxide, 1 Chrome Oxide

    Dark Water Blue, Reduction cone 10 on Stoneware. Sub 2 Iron Chromate for 1 Red Iron Oxide, 1 Chrome Oxide

    Dark Water Blue, Reduction cone 12 on Porcelain. No Iron Chromate

    Dark Water Blue, Reduction cone 12 on Porcelain. No Iron Chromate

    Blue 4

    This recipe calls for 13% additional Ultrox, which I don’t have.  I tried substituting with Zircopax, the result is kind of strange.

    Blue 4, Reduction cone 10 on Porcelain. Sub Ultrox for Zircopax

    Blue 4, Reduction cone 10 on Stoneware. Sub Ultrox for Zircopax

  • Jingdezhen

    Porcelain Stone

    Tests of local porcelain stone, glaze stone and glaze ash at a local materials shop in Jingdezhen.

  • Jingdezhen

    Glaze Ash

  • Glazes

    Porcelain Stone Glazes

    Jingdezhen Porcelain Stone

    There are a number of types of porcelain stone mined throughout Jingdezhen and the surrounding countryside.  Some are more suitable for making porcelain clay, while others are traditionally used for glazes.  It is difficult to know how similar modern-day porcelain stone is to traditional materials.  During the few years I have lived in Jingdezhen, some mines have been closed off to private mining, while others have simply run out of material.  Those still operating often mix poor-quality material with good material in order to increase production.  And plaster is added in ever increasing amounts in order to make the porcelain stone bricks less likely to break in transit.

    Below are three types of porcelain stone fired to 1310 Celsius in a reduction atmosphere.  From left to right:  San Bao porcelain stone, Yaoli glaze stone #1, Yaoli glaze stone #2.

    Most porcelain stone is made from a combination of rocks.  The stones below are used to make Yaoli glaze stone.  On the left is the more common, dirtier stone, in the middle is the higher quality stone, while the right is the mixed, washed and purified stone before adding plaster.  All examples were fired to 1310 Celsius in reduction atmosphere.

    San Bao Porcelain Stone (三宝瓷石)

    Below are some simple tests of porcelain stone from San Bao Village (三宝瓷石).  This stone is often used for making traditional porcelain clay, but it can also be used for glazes.  (However, usually “glaze stone”, or 釉果, is used for glazes.)

    The only chemical analysis I have found for San Bao Porcelain Stone comes from 陶瓷艺术釉工艺学 published by 江西高校出版社:

    SiO2: 7.013, Al2O3: 17.64, Fe2O3: 0.69, CaO: 0.54, MgO: 0.09, K20: 4.02, Na2O: 4.68.  LOI 2.01

    (The SiO2 amount is most likely a typo, they probably intended to write 70.13.)

    However, this analysis can only be used as a basic guideline.  There are noticeable differences between the porcelain stone produced by various families in San Bao, and quality seems to change every year.

    Traditional glaze recipes usually call for whiting, but unless fired very carefully, porcelain stone has a tendency to carbon-trap when whiting is the flux.  Replacing whiting with wollastonite eliminates this problem.

    Below are a few glazes containing San Bao porcelain stone, silica, wollastonite and kaolin.  It is quite easy to make a very nice celadon with porcelain stone.

    Yaoli Glaze Stone (瑶里釉果)

    Yaoli Glaze Stone (瑶里釉果) is traditionally used for creating glazes.  As with San Bao porcelain stone, there are a number of families mining, cleaning, and creating the glaze stone bricks sold in Jingdezhen.

    陶瓷艺术釉工艺学 has the following analysis:

    SiO2: 73.99, Al2O3: 15.55, Fe2O3: 0.37, CaO: 1.76, MgO: 0.33, K20: 2.88, Na2O: 2.63.  LOI 2.88

    But again, the material varies from seller to seller and from year to year.

    At the left is a simple melt test of 75% glaze stone with 25% Wollastonite and 80% glaze stone with 20% Wollastonite.  The 20% Wollastonite version is already a perfectly useable celadon.

    Below are a few simple celadons made with glaze stone, silica, wollastonite, and kaolin.

    Porcelain Bodies

    A test of 80% porcelain stone and 20% kaolin (New Zealand halloysite).  This porcelain is particularly white and fairly translucent.  It is quite nice to throw but fragile when bone dry.  Mixtures of various types of porcelain stone with between 10-40% kaolin produce porcelain bodies suitable for a range of temperatures.

  • Glazes

    Black Glazes

    All of the following ash glaze recipes and more can now be found on my new open-source ceramics recipes website, Glazy:  http://glazy.org/search?category=36&subcategory=78

    Here are a few black glazes, mostly from John Britt’s book High Fire Glazes.  You can find these recipes and more on my glaze website Glazy: http://glazy.org/search?search_words=&category=36&subcategory=78&cone=high&atmosphere=0&surface=0&transparency=0

    Val's Satin Black

    From Val Cushing.

    • Custer Feldspar: 20
    • Soda Feldspar: 20
    • Whiting: 2
    • Silica: 20
    • Ball Clay: 10
    • Talc: 13
    • Dolomite: 15
    • Add: Red Iron Oxide: 3
    • Add: Manganese Dioxide: 2
    • Add: Cobalt Oxide: 3
    • Add: Chrome Oxide: 1

    Porcelain, Orton Cone 10 Reduction

    Stoneware, Orton Cone 10 Reduction

    Val's Satin Black Variation

    From Ceramic Arts Daily:

    • Custer Feldspar: 20
    • Soda Feldspar: 20
    • Whiting: 2
    • Silica: 20
    • Ball Clay: 10
    • Talc: 13
    • Dolomite: 15
    • Add: Red Iron Oxide: 9
    • Add: Cobalt Carbonate: 3

    Porcelain, Orton Cone 10 Reduction

    Stoneware, Orton Cone 10 Reduction

    Fat Black

    From The Complete Guide to High-Fire Glazes:

    • Custer Feldspar: 32.7
    • Whiting: 15.4
    • Silica: 32.7
    • Kaolin: 9.6
    • Ball Clay: 9.6
    • Add: Red Iron Oxide: 8
    • Add: Cobalt Carbonate: 3.8
    • Add: Bentonite: 2

    Porcelain, Orton Cone 10 Reduction

    Stoneware, Orton Cone 10 Reduction

  • Glazes

    Kaki (Persimmon, Tomato) Glaze

    Here are a few Kaki glazes, mostly from John Britt’s book High Fire Glazes.  You can find these recipes (with updated cone 9 & 10 photos)  and more on my glaze website Glazy: http://glazy.org/search?search_words=&category=36&subcategory=47&cone=high

    Coleman Kaki

    Custer Feldspar 48, Silica 16, Whiting 9, Kaolin 7, Talc 9, Bone Ash 11, Red Iron Oxide 11.5

    Coleman Kaki 1280 Oxidation

    Coleman Kaki 1280 Oxidation

    Coleman Kaki 1310 Reduction

    Coleman Kaki 1310 Reduction

    Coleman Kaki 1300 Reduction Slower Cool

    Coleman Kaki 1300 Reduction Slower Cool

    Coleman Kaki 1300 Reduction Slower Cool

    KC Red Kaki

    Custer Feldspar 45.7, Silica 24.5, Whiting 6.4, Kaolin 6.4, Magnesium Carbonate 6.4, Bone Ash 10.6, Red Iron Oxide 6.4

    KC Red Kaki 1310 Reduction

    KC Red Kaki 1310 Reduction

    KC Red Kaki 1280 Oxidation

    KC Red Kaki 1280 Oxidation

    Anderson Ranch Kaki

    Custer Feldspar 45, Silica 20, Whiting 7, Kaolin 8, Talc 8, Bone Ash 12, Red Iron Oxide 13.5

    Anderson Ranch Kaki 1310 Reduction

    Anderson Ranch Kaki 1310 Reduction

    Anderson Ranch Kaki 1280 Oxidation

    Anderson Ranch Kaki 1280 Oxidation

    Anderson Ranch Kaki 1300 Reduction Slower Cool

    Anderson Ranch Kaki 1300 Reduction Slower Cool

    Anderson Ranch Kaki 1300 Reduction Slower Cool

    Staley's Kaki

    Custer Feldspar 48, Silica 26, Kaolin 7, Magnesium Carbonate 7, Bone Ash 12, Red Iron Oxide 8

    Staley's Kaki 1310 Reduction

    Staley's Kaki 1310 Reduction

    Staley's Kaki 1280 Oxidation

    Staley's Kaki 1280 Oxidation

    Kaki

    Custer Feldspar 30, Silica 20, Kaolin 20, Dolomite 15, Bone Ash 15, Red Iron Oxide 10

    Kaki Kaki 1310 Reduction

    Kaki Kaki 1280 Oxidation

    Kaki Kaki 1280 Oxidation

    Val's Tomato Red

    F-4 Feldspar 45, Silica 24, Whiting 7, Kaolin 7, Magnesium Carbonate 6, Bone Ash 11, Red Iron Oxide 8

    Val's Tomato Red 1310 Reduction

    Val's Tomato Red 1310 Reduction

    Val's Tomato Red 1280 Oxidation

    Val's Tomato Red 1280 Oxidation

    Chinese Glazes Russet Ding

    Left:  Potash Feldspar 26, Silica 25.5, Kaolin 34.5, Dolomite 10, Titanium Dioxide 1, Red Iron Oxide 10

    Right:  Potash Feldspar 30.5, Silica 30, Kaolin 28.5, Dolomite 7, Titanium Dioxide 1, Red Iron Oxide 5.5

    Chinese Glazes Russet Ding 1 1310 Reduction

    Chinese Glazes Russet Ding 2 1310 Reduction

  • Glazes

    Tianmu (Temmoku) Glazes

    Here are a few Tenmoku glazes, mostly from John Britt’s book High Fire Glazes.  You can find these recipes and more on my glaze website Glazy: http://glazy.org/search?search_words=&category=36&subcategory=44&cone=high&atmosphere=0&surface=0&transparency=0

    Hamada Temmoku

    Custer Feldspar 50, Silica 30, Whiting 20, Red Iron Oxide 9

    Leach Temmoku

    Custer Feldspar 40, Silica 30, Whiting 20, Kaolin 10, Red Iron Oxide 9

    Rust Black

    Custer Feldspar 46.2, Silica 23.2, Whiting 17.4, Kaolin 10.9, Zinc Oxide 2.3, Yellow Iron Oxide 11.2

    Jeff's Temmoku

    Custer Feldspar 53.8, Silica 22.4, Whiting 12.9, Kaolin 6, Barium Carbonate 2.5, Zinc Oxide 2.5, Red Iron Oxide 8.9

    Secrest Temmoku

    Custer Feldspar 53, Silica 24, Whiting 12, Kaolin 6, Barium Carbonate 2.5, Zinc Oxide 2.5, Red Iron Oxide 10

    Mark's Temmoku

    Custer Feldspar 45, Silica 27, Whiting 17, Kaolin 11, Red Iron Oxide 10

    Johnston Temmoku

    Custer Feldspar 59.1, Silica 23.4, Whiting 12.7, Kaolin 4.9, Red Iron Oxide 7.7

    Roy Temmoku

    Custer Feldspar 58.7, Silica 21.7, Whiting 12.4, Bell Dark Ball Clay (sub regular Ball Clay) 7.2, Red Iron Oxide 7.7