Articles

  • Jingdezhen

    Sanbao Porcelain Stone and Saggar Kiln

    Nestled in the beautiful mountains near Jingdezhen is Sanbao, a traditional source of porcelain stone. Porcelain stone comes in many types characterized by the local geography. Sanbao stone is primarily used in making porcelain bodies, but it can also be used in glazes.

    Worker removing porcelain stone from the Sanbao mine (May 2012)

    This wooden tool ensures equally sized porcelain bricks.

    Porcelain bricks are air-dried on wooden racks.

    A shrine at the mine.

    A workshop near the porcelain stone mine specializes in making kiln saggars.

  • Glazes

    Ash 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=96

    I’m not particularly an ash glaze aficionado, and I’m far from an expert.  But it’s surprisingly easy to make an interesting ash glaze, and it’s nice to have some “natural” glazes which give interesting surfaces on functional ware.  

    The digitalfire website has safety tips for mixing and using ash glazes.

    At the bottom of this article is a list of resources for learning more.

    Wood stove ash with local stoneware

    A great way to make an ash glaze is to mix any type of ash with your stoneware body.  A line blend of ash from 40-60% is a good place to start.

    Below are tests of a local Jiangxi stoneware body, Tianbao, mixed with unwashed ash from my wood stove.  Glazes dipped onto bisqued porcelain and dark stoneware tiles, then fired in reduction to Orton Cone 10.

    Stoneware 40% Wood Ash 60%. Orton Cone 10 Reduction.

    Stoneware 40% Wood Ash 60%. Orton Cone 10 Reduction.

    Stoneware 50% Wood Ash 50%. Orton Cone 10 Reduction.

    Stoneware 50% Wood Ash 50%. Orton Cone 10 Reduction.

    Rice Straw Ash with Local Stoneware

    Below are tests of a local Jiangxi stoneware body, Tianbao, with Rice Straw Ash.

    Clay 60% Straw Ash 40%. Orton Cone 10 Reduction.

    Clay 50% Straw Ash 50%. Orton Cone 10 Reduction.

    Clay 40% Straw Ash 60%. Orton Cone 10 Reduction.

    Glaze Ash with Local Stoneware

    Below are tests of a local Jiangxi stoneware body, Tianbao, with a traditional Jingdezhen glaze ash called Er Hui.

    20% Glaze Ash

    30% Glaze Ash

    40% Glaze Ash

    50% Glaze Ash

    High Fire Glazes Ash Recipes

    Some ash glazes from The Complete Guide to High Fire Glazes  All tests fired to Orton Cone 10 in reduction.

    Basic Ash

    Titus-Zella Wood Ash

    This recipe, listed in High-Fire Glazes, is simply 50% wood ash and 50% custer feldspar.

    Basic Aerni Ash

    Zellar Ash

    Other Ash Glaze Recipes

    Leach Ash

    As posted by Tom Turner (link below).  He says: “I do not wash ash as I believe much of the character is in what is washed away. Dry sieve through a 30 mesh sieve.”  I used a 60 mesh sieve.

    Leach’s Basic Ash Glaze
    Wood Ash 40
    Feldspar 40
    Ball Clay 20

    Libby Pickard Ash Glaze

    From Phil Rogers Ash Glazes, p. 85:
    https://books.google.com/books?id=th3JZzIFFYQC

    Also listed on Glazy:  http://glazy.org/recipes/4407

    Tenmoku with Rice Straw Ash

    This glaze is from a University of Texas online glaze database (approx 2004) at: http://general.utpb.edu/fac/stanley_c/
    http://general.utpb.edu/fac/stanley_c/formulae/glaze/tenmokus.htm

    More information on Glazy:  http://glazy.org/recipes/3500

    Synthetic (Fake) Ash

    You must burn a lot of wood or plant matter to make a small amount of useable ash.  The sieved, unwashed ash collected after a Winter burning my small wood furnace only gives me enough material to make a couple buckets of 50% clay 50% ash glaze.  Furthermore, I burn whatever type of wood happens my way, and it often contains impurities like dirt and nails.  So besides the limited quantity I have available, there is also a question of consistency.

    Substituting part or all of real ash with synthetic ash in a glaze recipe is one method to address the problems of impurities, variability, and supply.

    For most of these tests I just made a simple 50/50 mix of the synthetic ash recipe with a local stoneware body in order to compare to my previous real wood ash glazes.  The following tests were all fired to Orton Cone 11 in reduction.

    Robert Tichane's Recipe

    Robert Tichane’s excellent book Ash Glazes has a chapter devoted to synthetic ash glazes.  Based on Dr. Emil Wolff’s analysis of Beech wood ash, Tichane creates the following synthetic ash:

    • Limestone: 75 g (43.2%)
    • Dolomite: 50 g (30.8%)
    • Potassium Carbonate: 25 g (15.4%)
    • Bone Ash: 6 g (3.7%)
    • Sodium Carbonate: 5 g (3.1%)
    • Calcium Sulfate: 3 g (1.9%)
    • Silica: 2 g (1.2%)
    • Sodium Chloride: 0.2 g (0.1%)
    • Ferric Oxide: 1 g (0.6%)

     

    Robert Tichane's Synthetic Ash 100%

    As you can see in the third picture, the soluble salts tend to permeate bisque ware, possibly decreasing body melting temperature and increasing warping.  (It would be interesting to compare the effects of solubles on a raw-glazed tile.)  Solubles are troublesome for other reasons, of course.  Water should not be removed from an already mixed glaze batch, and safety is a concern.

     

    Tichane Synthetic Ash 100%. Porcelain, Orton Cone 11 Reduction.

    Tichane Synthetic Ash 100%. Stoneware, Orton Cone 11 Reduction.

    Tichane Synthetic Ash 100%. Porcelain, Orton Cone 11 Reduction.

    Robert Tichane's Synthetic Ash 50%, Stoneware 50%

    Tichane’s recipe is interesting because of the soluble components that emulate unwashed wood ash.  And of all the synthetic ash recipes I tested, Tichane’s comes closest to the feel of real unwashed wood ash glazes.

    Porcelain, Orton Cone 11 Reduction.

    Stoneware, Orton Cone 11 Reduction.

    Maritaro Onishi's Recipe

    Ash Glazes also contains a recipe for synthetic ash by Maritaro Onishi:

    • Limestone: 62%
    • Feldspar: 12%
    • Bone Ash: 7%
    • Magnesite (Magnesium Carbonate): 5%
    • Kaolin: 10%
    • Silica: 3%

    Maritaro Onishi's Synthetic Ash 50%, Stoneware 50%

    Tichane notes that impurities in the feldspar and kaolin may add iron and manganese.  However, in my test I added an additional 2% red iron oxide and 1.2% manganese dioxide.

    Porcelain, Orton Cone 11 Reduction

    Stoneware, Orton Cone 11 Reduction

    Etsuzo Katou's Recipe

    John Neely on the Clayart mailing list mentions Etsuzo Katou who published another synthetic ash recipe, Ueda synthetic ash #3:

    • Whiting: 59%
    • Potash Feldspar: 22%
    • Magnesium Carbonate: 11%
    • Bone Ash: 5%
    • Red Iron Oxide: 2%
    • Manganese Dioxide: 1%

    Etsuzo Katou's Synthetic Ash 50%, Stoneware 50%

    I accidentally used 2% Manganese in my test glaze.

    Porcelain, Orton Cone 11 Reduction

    Stoneware, Orton Cone 11 Reduction

    Joseph Grebanier's Recipe

    In chapter 13 of Chinese Stoneware Glazes, Synthetic Wood Ash, Joseph Grebanier compares various wood ash analyses and questions the accuracy of Onishi’s synthetic ash formula.  Using Herbert Sanders’ ash analyses in The World of Japanese Ceramics,  Grebanier creates the following recipes:

    Grebanier’s Batch Recipe for Synthetic “Common Ash”:

    • Whiting: 35.73%
    • Buckingham Feldspar: 24.35%
    • Kaolin: 10.39%
    • Flint: 10.11%
    • Magnesium Carbonate: 6.86%
    • Bone Ash: 4.09%
    • Soda Ash: 3.90%
    • Red Iron Oxide: 3%
    • Manganese Dioxide: 1.32%

    Grebanier’s “Common Ash” recipe was later simplified by Phil Rogers in Ash Glazes:

    • Whiting: 36%
    • Buckingham Feldspar: 25%
    • Kaolin: 10%
    • Flint: 10%
    • Magnesium Carbonate: 7%
    • Bone Ash: 5%
    • Soda Ash: 4%
    • Red Iron Oxide: 3%
    • Manganese Dioxide: 1%

    Grebanier’s Batch Recipe for Synthetic Pine Ash:

    • Whiting: 44.37%
    • Orthoclase: 36.17%
    • Magnesium Carbonate: 6.36%
    • Soda Ash: 4.38%
    • Bone Ash: 4.1%
    • Red Iron Oxide: 2.31%
    • Manganese Dioxide: 2.28%

    Grebanier’s Pine Ash recipe was later simplified by Robert Tichane in his Ash Glazes:

    • Whiting: 44.4%
    • Feldspar: 36.2%
    • Magnesium Carbonate: 6.4%
    • Soda Ash: 4.4%
    • Bone Ash: 4.1%
    • Red Iron Oxide: 2.3%
    • Manganese Dioxide: 2.3%

    Grebanier's Synthetic Common Ash Recipe (simplified)

    In the following tests I substituted Buckingham Feldspar for my local Potash Feldspar.

    50% Stoneware, %50 Synthetic Ash. Porcelain, Orton Cone 11 Reduction

    50% Stoneware, %50 Synthetic Ash. Stoneware, Orton Cone 11 Reduction

    40% Stoneware, %60 Synthetic Ash. Porcelain, Orton Cone 12 Reduction

    40% Stoneware, %60 Synthetic Ash. Stoneware, Orton Cone 12 Reduction

    Leach’s Basic Ash Glaze. Wood Ash (sub Synthetic Ash) 40, Feldspar 40, Ball Clay 20. Porcelain, Orton Cone 12 Reduction

    Leach’s Basic Ash Glaze. Wood Ash (sub Synthetic Ash) 40, Feldspar 40, Ball Clay 20. Stoneware, Orton Cone 12 Reduction

    Grebanier's Synthetic Pine Ash Recipe (simplified)

    Stoneware Body 50%, Synthetic Pine Ash 50%. Porcelain, Orton Cone 12 Reduction

    Stoneware Body 50%, Synthetic Pine Ash 50%. Stoneware, Orton Cone 12 Reduction

    Synthetic Ashes in Low-iron Glazes

    Many white, clear, and celadon glazes in antiquity were at least in part comprised of plant or tree ash.  By varying the amount of synthetic ash and coloring oxides (mostly iron and manganese) you can quite easily produce some nice glazes.

    One of the most important lessons to learn from using synthetic ash is not necessarily to reproduce the look/effect of natural ashes, but rather to understand the result of introducing a wider variety of oxides into the glaze mix.  For instance, take a common celadon recipe, Hamada 5-3-2 (50% custer feldspar, 30% silica, 20% whiting) which is primarily fluxed with lime.  What happens when we introduce extra sodium, potassium, magnesium, phosphorus, iron and manganese to the mix?

    Grebanier Synthetic Common Ash and Porcelain Body

    One of my favorite ways of making new glazes is to simply mix a flux or ash with a clay body.  This method is usually used with iron-rich stonewares but works just as well for cleaner stoneware and porcelain bodies.

     

    Porcleain Body 60%, Synthetic Wood Ash 40%. Orton Cone 12 Reduction

    Porcleain Body 50%, Synthetic Wood Ash 50%. Orton Cone 12 Reduction

    Porcleain Body 40%, Synthetic Wood Ash 60%. Orton Cone 12 Reduction

    Grebanier Synthetic Common Ash, reduced Iron and Manganese

    For the following three tests, the amount of Iron and Manganese in the synthetic ash was reduced to 1/3 of the original amount.

    The first test results in a lovely semi-matte glaze, while the last two tests are passable celadons.

    Porcleain Body 60%, Synthetic Wood Ash 40%. Orton Cone 12 Reduction

    Porcleain Body 50%, Synthetic Wood Ash 50%. Orton Cone 12 Reduction

    Porcleain Body 40%, Synthetic Wood Ash 60%. Orton Cone 12 Reduction

    Grebanier Synthetic Common Ash and Feldspar

    This is basically the Titus-Zella Wood Ash above.

    Potash 60%, Synthetic Wood Ash 40%. Orton Cone 12 Reduction

    Potash 50%, Synthetic Wood Ash 50%. Orton Cone 12 Reduction

    Adjusting the Feldspar/Synthetic Wood Ash glazes

    For the potash feldspar/synthetic wood ash mixes above, I reduced the amount of iron and manganese (1/3 of original recipe) as well as added silica to reduce crazing.  With 10% Silica we’ve eliminated the crazing.

    Potash 55%, Silica 5%, Synthetic Wood Ash 40%. Orton Cone 12 Reduction

    Potash 50%, Silica 10%, Synthetic Wood Ash 40%. Orton Cone 12 Reduction

    Making Your Own Synthetic Ash

    Chemical analyses of ash vary widely, even analyses by different people of the same type of ash.  But chemical analyses are a good starting point for experimentation.  Synthetic ash recipes can be calculated by hand (see Chapter 13 of Nigel Wood’s Chinese Glazes) or by using glaze software.

    I was interested in Issu wood ash, commonly used in Japan for making celadon glazes.  The chemical analyses for Issu wood  (see list by Linda Arbuckle below) are:

    SiO2 Al2O3 TiO2 Fe2O3 CaO MgO K2O Na2O MnO P2O5
    Herbert Sanders, The World of Japanese Ceramics 34.6 4.38 0.49 47.71 5.99 2.51 0.06 0.33 3.93
    Cardew 16.19 4.16 0.92 36.68 6.6 1 0.2 0.48 0.92
    J.B.E. Patterson (via Leach, A Potter’s Book) 71.96 0.63 0.28 15.95 1.57 0.84 0.42

    As you can see, there’s a huge difference between these three analyses, it’s difficult to know if any of them are to be trusted.  So I checked Grebanier’s Chinese Stoneware Glazes and was surprised to find that he had come across the exact same problem (Chapter 13, Synthetic Wood Ash).  Grebanier seems to have abandoned hope of finding an Issu ash substitute, but I went ahead with Sanders’ analysis as it seemed more trustworthy.

    (Actually, perhaps it’s not that Sanders’ analysis is more trustworthy as much as the fact that it’s more interesting to me.)

    I calculated two recipes, one using only Whiting and one minimizing the amount of Whiting by using Wollastonite (without adding too much Silica) and replacing Magnesium Carbonate with Dolomite (in order to provide MgO as well as CaO).

    Recipe 1 (Whiting):

    • Whiting 53.36
    • Custer Feldspar 13.97
    • Silica 13.76
    • Magnesium Carb 9.72
    • Bone Ash 6.63
    • New Zealand Kaolin 2.03
    • Iron 0.31
    • Manganese Dioxide 0.23
    • Total: 100.01

    Recipe 2 (Minimize Whiting):

    • Whiting 21.35
    • Wollastonite 29.86
    • Dolomite 23.14
    • Custer Feldspar 15.46
    • Bone Ash 7.34
    • New Zealand Kaolin 2.25
    • Iron 0.35
    • Manganese Dioxide 0.26
    • Total: 100.01

    Ash Glazes Resources

    Ash Glazes by Robert Tichane.

    The Complete Guide to High Fire Glazes by John Britt.  Besides being my favorite introduction book on glazes, there is a section on ash and synthetic ash glazes.

    Chinese Stoneware Glazes by Joseph Grebanier.  Joseph uses ash in many of his glazes in order to re-create ancient Chinese glazes.

    Ash Glazes by Phil Rogers.  I have not yet read this book, but the reviews are good and the book preview on Google Books looks promising.

    Ash Glaze on the Digitalfire.com website.  Also information on wood ash, hardwood ash, softwood ash, rice straw ash,  and rice husk ash.

    Nigel Wood’s Chinese Ceramics and Science and Civilisation in China: Volume 5, Chemistry and Chemical Technology, Part 12, Ceramic Technology both contain a wealth of information of the role of wood and plant ash in the development of Chinese glazes, including chemical analyses of ashes and comparisons with glaze compositions.

    Some ash glaze recipes can be found on Rick’s Bricks and Tom Turner’s website.

    Chemical Analyses of Various Ashes

    The following information is from a Linda Arbuckle handout, GlazeChem Materials.

    Bamboo ash

    % 4.8 K2O 0.3 CaO 86.4 SiO2 0.4 Fe2O3 8.1 LOI

    Bamboo ash supplies several oxides, especially SiO2.

    Analyses:

    Cardew:

    % 4.8 K2O 0.3 CaO 86.4 SiO2 0.4 Fe2O3 8.1 LOI

    (‘Bamboo sugar’, Java) (Bourry, 1st English edition, 1901)

    Barley straw ash

    % 5 Na2O 22 K2O 3 MgO 8 CaO 57 SiO2 5 P2O5

    Barley straw ash supplies several oxides, especially SiO2 and K2O.

    Analyses:

    Hamer & Hamer:

    % 5 Na2O 22 K2O 3 MgO 8 CaO 57 SiO2 5 P2O5

    Beech ash

    % 8.34 Na2O 24.29 K2O 8.20 MgO 42.00 CaO 3.01 SiO2 6.2 P2O5 0.62 Fe2O3 4.52 MnO 2.10 SO3 0.72 Cl

    Beech ash supplies several oxides, especially CaO and K2O.

    Analyses:

    Rogers:

    % 8.34 Na2O 24.29 K2O 8.20 MgO 42.00 CaO 3.01 SiO2 6.2 P2O5 0.62 Fe2O3 4.52 MnO 2.10 SO3 0.72 Cl

    Rogers (appendix):

    % 4.0 Na2O 16.5 K2O 10.9 MgO 55.5 CaO 5.45 SiO2 5.45 P2O5 1.0 Fe2O3

    Birch ash

    % 9 Na2O 22.6 K2O 14.3 MgO 29.6 CaO 11.5 SiO2 7.9 P2O5 1.3 Fe2O3 0.4 MnO 3.4 LOI

    Birch ash supplies several oxides, especially CaO and K2O.

    Analyses:

    Conrad:

    % 9 Na2O 22.6 K2O 14.3 MgO 29.6 CaO 11.5 SiO2 7.9 P2O5 1.3 Fe2O3 0.4 MnO

    Rogers (appendix):

    % 7.69 Na2O 12.53 K2O 7.69 MgO 57.5 CaO 3.84 SiO2 7.69 P2O5 1.0 Fe2O3

    Hamer & Hamer:

    % 9 Na2O 18 K2O 11 MgO 45 CaO 4 Al2O3 8 SiO2 4 P2O5 1 Fe2O3

    Cedar ash

    % 3.7 Na2O 4.3 K2O 6 MgO 44.2 CaO 0.52 Al2O3 24.28 SiO2 10.6 P2O5 1.01 Fe2O3 0.3 MnO 5.09 LOI

    Cedar ash supplies several oxides, especially CaO and SiO2.

    Analyses:

    Conrad:

    % 3.7 Na2O 4.3 K2O 6 MgO 44.2 CaO 0.52 Al2O3 24.28 SiO2 10.6 P2O5 1.01 Fe2O3 0.3 MnO

    Common ash

    % 2.33 Na2O 3.91 K2O 3.3 MgO 22.42 CaO 8.91 Al2O3 30.99 SiO2 1.91 P2O5 3.04 Fe2O3 1.26 MnO 21.44 LOI

    Common ash supplies several oxides, especially SiO2 and CaO.

    Analyses:

    Sanders:

    % 2.33 Na2O 3.91 K2O 3.3 MgO 22.42 CaO 8.91 Al2O3 30.99 SiO2 1.91 P2O5 3.04 Fe2O3 1.26 MnO 21.44 LOI

    Desert plant ash

    % 28.0 Na2O 5.5 K2O 0.5 MgO 21.1 CaO 1.8 P2O5 34.0 CO2

    Desert plant ash supplies several oxides, especially Na2O and CaO.

    Analyses:

    Tichane (TCB): (adds to 91%)

    % 28.0 Na2O 5.5 K2O 0.5 MgO 21.1 CaO 1.8 P2O5 34.0 CO2

    Elder ash

    % 2 Na2O 17 K2O 16 MgO 38 CaO 14 SiO2 13 P2O5

    Elder ash supplies several oxides, especially CaO.

    Analyses:

    Hamer & Hamer:

    % 2 Na2O 17 K2O 16 MgO 38 CaO 14 SiO2 13 P2O5

    Fern ash

    % 0.56 Na2O 4.81 K2O 7.44 MgO 8.59 CaO 19.32 Al2O3 55.02 SiO2 0.3 TiO2 0.92 P2O5 1.67 Fe2O3 1.36 MnO

    Fern ash supplies several oxides, especially SiO2 and Al2O3.

    Analyses:

    Rogers (appendix):

    % 0.56 Na2O 4.81 K2O 7.44 MgO 8.59 CaO 19.32 Al2O3 55.02 SiO2 0.3 TiO2 0.92 P2O5 1.67 Fe2O3 1.36 MnO

    Hamer & Hamer: (Bracken and fern)

    % 3 Na2O 26 K2O 8 MgO 12 CaO 10 Al2O3 33 SiO2 6 P2O5 1 Fe2O3 1 MnO

    Grass ash

    0.2 KNaO 0.3 MgO 0.5 CaO 0.2 Al2O3 2.0 SiO2

    Grass ash supplies several oxides, especially SiO2 and CaO.

    Generic grass ash.

    Green: (weed and grass ash)

    0.2 KNaO 0.3 MgO 0.5 CaO 0.2 Al2O3 2.0 SiO2

    Green: (unwashed lawn clippings, from Leach “A Potter’s Book”)

    0.41 KNaO 0.29 MgO 0.30 CaO 0.27 Al2O3 1.09 SiO2 0.12 P2O5 0.03 Fe2O3

    Green: (washed lawn clippings, from Leach “A Potter’s Book”)

    0.15 KNaO 0.32 MgO 0.53 CaO 0.38 Al2O3 1.52 SiO2 0.15 P2O5 0.05 Fe2O3

    Rogers: (Lawn grass)

    % 6.20 Na2O 6.19 K2O 5.65 MgO 12.88 CaO 16.60 Al2O3 39.64 SiO2 9.00 P2O5 3.44 Fe2O3

    Hamer & Hamer: (Lawn grass)

    % 3 Na2O 5 K2O 5 MgO 10 CaO 11 Al2O3 59 SiO2 5 P2O5 2 Fe2O3

    Mixed hardwood ash

    % 9.12 Na2O 14 K2O 12 MgO 30 CaO 0.1 Al2O3 15.3 SiO2 13.1 P2O5 2.4 Fe2O3 0.1 MnO 3.88 LOI

    Hearth ash

    % 0.55 Na2O 1.49 K2O 5.44 MgO 35.9 CaO 3.69 Al2O3 14.08 SiO2 2.14 P2O5 0.94 Fe2O3 34.32 h3O 0.14 MnO

    Hearth ash supplies several oxides, especially CaO and SiO2.

    Analyses:

    Cardew:

    % 0.55 Na2O 1.49 K2O 5.44 MgO 35.9 CaO 3.69 Al2O3 14.08 SiO2 2.14 P2O5 0.94 Fe2O3 34.32 h3O 0.14 MnO

    (Hearth ash (‘Dobai’), Japan (E. Kato, Interceram, 2 (1962), 110).)

    Heather ash

    % 9 Na2O 12 K2O 10 MgO 21 CaO 41 SiO2 5 P2O5 2 Fe2O3

    Heather ash supplies several oxides, especially SiO2 and CaO.

    Analyses:

    Hamer & Hamer:

    % 9 Na2O 12 K2O 10 MgO 21 CaO 41 SiO2 5 P2O5 2 Fe2O3

    Issu-wood ash

    % 0.06 Na2O 2.51 K2O 5.99 MgO 47.71 CaO 4.38 Al2O3 34.6 SiO2 3.93 P2O5 0.49 Fe2O3 0.33 MnO

    Isu-wood ash supplies several oxides, especially CaO and SiO2.  Issu (Distylium racemosum) is the source of a very popular wood ash in Japan. Note the incredible variations in the analyses.

    Analyses:

    Sanders:

    % 0.06 Na2O 2.51 K2O 5.99 MgO 47.71 CaO 4.38 Al2O3 34.6 SiO2 3.93 P2O5 0.49 Fe2O3 0.33 MnO

    Cardew:

    % 0.2 Na2O 1 K2O 6.6 MgO 36.68 CaO 4.16 Al2O3 16.19 SiO2 3.67 P2O5 0.92 Fe2O3 30.08 h3O 0.8 SO3 0.48 MnO

    (Isu Ash from Hagi, Japan (E. Kato, Interceram, 2 (1962), 110).)

    Leach (“A Potter’s Book”):

    % 0.84 K2O 1.57 MgO 15.95 CaO 0.63 Al2O3 71.96 SiO2 0.42 P2O5 0.28 Fe2O3 8.29 LOI

    (from work done by J.B.E. Patterson)

    Ivy ash

    % 20 Na2O 26 K2O 8 MgO 25 CaO 12 SiO2 6 P2O5 3 Fe2O3

    Ivy ash supplies several oxides, especially CaO, K2O, and Na2O.

    Analyses:

    Hamer & Hamer:

    % 20 Na2O 26 K2O 8 MgO 25 CaO 12 SiO2 6 P2O5 3 Fe2O3

    Larch wood ash

    % 9 Na2O 21 K2O 8 MgO 27 CaO 1 Al2O3 11 SiO2 8 P2O5 4 Fe2O3 11 MnO

    Larch wood ash supplies several oxides, especially CaO, K2O, SiO2, and MnO.

    Analyses:

    Hamer & Hamer:

    % 9 Na2O 21 K2O 8 MgO 27 CaO 1 Al2O3 11 SiO2 8 P2O5 4 Fe2O3 11 MnO

    Mahogany ash

    % 10.98 Na2O 9.49 K2O 4.39 MgO 9.49 CaO 3.81 Al2O3 51.51 SiO2 2.08 P2O5 4.53 Fe2O3 3.72 LOI

    Mahogany ash supplies several oxides, especially SiO2.

    Analyses:

    Cardew:

    % 10.98 Na2O 9.49 K2O 4.39 MgO 9.49 CaO 3.81 Al2O3 51.51 SiO2 2.08 P2O5 4.53 Fe2O3

    (Australian white mahogany) (Forestry Commission of New South Wales, 1956)

    Maple ash

    % 6.04 Na2O 6.2 K2O 12.05 MgO 27.5 CaO 0.9 Al2O3 13.8 SiO2 8.1 P2O5 2.5 Fe2O3 0.5 MnO 22.41 LOI

    Maple ash supplies several oxides, especially CaO.

    Analyses:

    Conrad:

    % 6.04 Na2O 6.2 K2O 12.05 MgO 27.5 CaO 0.9 Al2O3 13.8 SiO2 8.1 P2O5 2.5 Fe2O3 0.5 MnO

    Meadow hay ash

    % 7.0 Na2O 25.67 K2O 5.0 MgO 11.56 CaO 29.57 SiO2 6.2 P2O5 1.0 Fe2O3

    Meadow hay ash supplies several oxides, especially SiO2 and K2O.

    Analyses:

    Rogers (appendix):

    % 7.0 Na2O 25.67 K2O 5.0 MgO 11.56 CaO 29.57 SiO2 6.2 P2O5 1.0 Fe2O3

    Hamer & Hamer: (Meadow grass)

    % 4 Na2O 15 K2O 5 MgO 10 CaO 3 Al2O3 58 SiO2 4 P2O5 1 Fe2O3

    Mixed wood ash

    0.125 Na2O 0.266 K2O 0.187 MgO 0.422 CaO 0.016 Al2O3 0.375 SiO2 0.109 P2O5 0.062 Fe2O3

     

    Oak ash

    % 9.12 Na2O 14 K2O 12 MgO 30 CaO 0.1 Al2O3 15.3 SiO2 13.1 P2O5 2.4 Fe2O3 0.1 MnO 3.88 LOI

    Oak ash supplies several oxides, especially CaO.

    Analyses:

    Conrad:

    % 9.12 Na2O 14 K2O 12 MgO 30 CaO 0.1 Al2O3 15.3 SiO2 13.1 P2O5 2.4 Fe2O3 0.1 MnO

    Tichane (TCB):

    % 3.9 Na2O 9.5 K2O 3.9 MgO 72.5 CaO 2.0 SiO2 5.8 P2O5

    Rogers: (English oak)

    % 9.12 Na2O 14.00 K2O 12.01 MgO 30.02 CaO 0.13 Al2O3 15.30 SiO2 13.8 P2O5 2.40 Fe2O3 0.10 MnO 0.05 CuO 2.61 SO3 1.18 Cl

    Rogers (appendix): (China)

    % 1.47 Na2O 5.77 K2O 4.09 MgO 23.54 CaO 15.11 Al2O3 39.81 SiO2 2.3 P2O5 3.58 Fe2O3 4.32 MnO

    Rogers (appendix): (Japan)

    % 1.52 Na2O 5.68 K2O 4.14 MgO 23.69 CaO 16.34 Al2O3 39.62 SiO2 2.62 P2O5 3.83 Fe2O3 1.01 MnO

    Hamer & Hamer:

    % 6 Na2O 11 K2O 9 MgO 51 CaO 1 Al2O3 10 SiO2 10 P2O5 1 Fe2O3 1 MnO

    Straw ash

    0.4 KNaO 0.2 MgO 0.4 CaO 2.7 SiO2 0.1 P2O5

    Straw ash supplies several oxides, especially SiO2.  Generic straw ash.

    Analyses:

    Green: (straw ash from cereal crops)

    0.4 KNaO 0.2 MgO 0.4 CaO 2.7 SiO2 0.1 P2O5

    Tallowwood ash

    % 6.84 Na2O 2.41 K2O 25.58 MgO 52.15 CaO 1.09 Al2O3 8.96 SiO2 0.4 P2O5 1.93 SO3 0.38 Cl2 0.18 MnO

    Tallowwood ash supplies several oxides, especially CaO and MgO.

    Analyses:

    Cardew:

    % 6.84 Na2O 2.41 K2O 25.58 MgO 52.15 CaO 1.09 Al2O3 8.96 SiO2 0.4 P2O5 1.93 SO3 0.38 Cl2 0.18 MnO

    (Eucalyptus microscorys III (Tallowwood) Forestry Commission of New South Wales, 1956)

    Thatching grass ash

    % 0.22 Na2O 2.55 K2O 3.67 MgO 6.14 CaO 5.42 Al2O3 76.96 SiO2 1.58 P2O5 0.22 TiO2 1.06 Fe2O3 0.15 SO3 0.67 MnO 1.4 LOI

    Thatching grass ash supplies several oxides, especially SiO2.

    Analyses:

    Cardew:

    % 0.22 Na2O 2.55 K2O 3.67 MgO 6.14 CaO 5.42 Al2O3 76.96 SiO2 1.58 P2O5 0.22 TiO2 1.06 Fe2O3 0.15 SO3 0.67 MnO 1.4 LOI

    (Abuja, Nigeria. Wahsed and calcined at 900C) (Overseas Geological Surveys, London, 1966)

    Turpentine ash

    % 4.08 Na2O 1.2 K2O 1.03 MgO 1.88 CaO 1.26 Al2O3 89.74 SiO2 0.39 P2O5 0.42 LOI

    Turpentine ash supplies several oxides, especially SiO2.

    Analyses:

    Cardew:

    % 4.08 Na2O 1.2 K2O 1.03 MgO 1.88 CaO 1.26 Al2O3 89.74 SiO2 0.39 P2O5

    (Australian turpentine) (Forestry Commission of New South Wales, 1956)

    Wheat straw ash

    % 2.8 Na2O 11.5 K2O 2.5 MgO 6.1 CaO 66.2 SiO2 5.4 P2O5 2.8 SO3 3.8 S

    Wheat straw ash supplies several oxides, especially SiO2 and K2O.

    Analyses:

    Cardew:

    % 2.8 Na2O 11.5 K2O 2.5 MgO 6.1 CaO 66.2 SiO2 5.4 P2O5 2.8 SO3 3.8 S

    (Air dried) (B.C.S., (1959), 59P)

    Green:

    0.67 K2O 0.14 MgO 0.19 CaO 0.71 Al2O3 4.95 SiO2 0.10 P2O5

    Tichane (TCB):

    % 2.8 Na2O 11.5 K2O 2.5 MgO 6.1 CaO 66.0 SiO2 5.4 P2O5 2.8 LOI

    Rogers:

    % 1.4 Na2O 13.6 K2O 2.5 MgO 5.8 CaO 67.5 SiO2 4.8 P2O5 0.6 Fe2O3

    Hamer & Hamer:

    % 2 Na2O 13 K2O 4 MgO 6 CaO 70 SiO2 5 P2O5

    Willow ash

    % 2.50 Na2O 49.80 K2O 8.26 MgO 20.21 CaO 0.05 Al2O3 4.44 SiO2 10.00 P2O5 1.25 Fe2O3 0.18 MnO 1.22 SO3 0.08 Cl

    Willow ash supplies several oxides, especially K2O, CaO, and P2O5.

    Analyses:

    Rogers:

    % 2.50 Na2O 49.80 K2O 8.26 MgO 20.21 CaO 0.05 Al2O3 4.44 SiO2 10.00 P2O5 1.25 Fe2O3 0.18 MnO

    1.22 SO3 0.08 Cl

    Hamer & Hamer:

    % 3 Na2O 51 K2O 9 MgO 21 CaO 5 SiO2 10 P2O5 1 Fe2O3

    Ash wood ash

    0.125 Na2O 0.266 K2O 0.187 MgO 0.422 CaO 0.016 Al2O3 0.375 SiO2 0.109 P2O5 0.062 Fe2O3

    Ash wood ash supplies several oxides, especially CaO and SiO2.

    Analyses:

    Hamer & Hamer:

    % 8 Na2O 17 K2O 12 MgO 27 CaO 1 Al2O3 24 SiO2 7 P2O5 4 Fe2O3

  • Tests

    How I Make Glaze Test Tiles

    I’ve tried all manner of methods for making test tiles- thrown, extruded, and slab.  Each type has advantages, but I’ve finally come to the safest, most economical and useful method for my needs.

    Assuming you have a fast way to make slabs, using this technique you can easily make a couple hundred test tiles in an afternoon.

    Hand-rolled slabs work fine.  The irregular edges can be saved and used to make the supporting triangles.  To attach the supports I use dry clay trimmings and pure vinegar.  The triangles are dipped into the vinegar slip for about two seconds, then wiggled into place on the test tile until the two slabs are firmly joined.  (I have tried this with all of my clays, from porcelains to stonewares, without problems.  However, your clay may differ.)

    Just after joining, the test tiles should be covered and dried slowly for the first day or so.  You may notice some cracking along the join line, but the join should be strong enough to last through bisque and glaze firings.

    Edges of hand-rolled slab used for support triangles

    Joining slip made with dry trimmings and vinegar

     

    If you have casting slip, the fastest way that I have found to make test tiles is to make a slipcast slab using a large, flat plaster table.  Supports are joined to tiles using the same casting slip.

    Cutting a slipcast porcelain slab

    A fork is used for texturing the test tiles.

    Type of clay is stamped onto back of each test tile

    These test tiles will not fall over (especially important as I often put tests in public kilns).  They can be stacked very closely in the kiln, and the height can be varied by choosing either the long or short end of the triangular support.  Because they are flat, they require less glaze for coverage (handy when using very small batches of material) but also show more area of glaze than an extruded column.  The hole in the base allows the tile to be hung on a glaze bucket or on a display.  I stamp the back of the tile with a code for the type of clay, and there is ample space to write information about the test using an underglaze pencil.

    Packed close in the kiln.

    Dipping in 20ml of glaze

    Right side double-dipped

    Full details written with underglaze pencil and permanent marker

    Taking photos with a styrofoam support

    The tiles should be quite thick in order to better absorb and support thicker layers of glaze.

    After dipping the face of the tile into a glaze, I dip one side (not the top) again in order to see different thicknesses.  (Double-dipping the top of the tile often results in the thicker glaze running down into the thinner area, sometimes resulting in a completely even coat after firing.)

    Using flat, square tiles I can dip twice while only using 20ml of glaze.  This is especially useful when doing triaxials or biaxials using the syringe method.

    The back of the tile has a lot of space for writing glaze information.  Before firing use an underglaze pencil (I use Amaco Black Pencils), after firing a permanent marker can be used to record the date and temperature.

    Another advantage of these square tiles is that they photograph very well.

    For my purposes, the best size for a test tile is 6cm or 7cm square.  This size is large enough to get a feel for what the glaze looks like, while small enough to be covered by only 20ml of mixed glaze (including a second dip).

    Conveniently, the supporting triangles are half the width of the tile, which allows for first cutting the slab into 6cm or 7cm columns.

    I know it seems really anal, but this cutting pattern saves clay and ensures the tiles all rest at the same angle, allowing for more accurate comparisons and tighter packing in the kiln.

  • 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

  • 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

  • Porcelain Body

    Natural Quarts and Mica additions to porcelain

    Test of adding natural quartz and mica to porcelain.

    Porcelain is Taida 609 fired to 1310 celsius in reduction.

    Top row: 5, 10, 15, 20% addition of silica to 100g porcelain slip
    Bottom row: 5, 10, 15, 20% addition of mica to 100g porcelain slip

    IMG_6430

    The natural quartz has a ton of impurities. Also I did not consistently grind or filter the quartz. Addition of quartz impedes translucency.

    IMG_6436

    I’m not sure exactly what type of mica I used. However, it seems pretty clean and of uniform particle size. Didn’t notice translucency affected much. The last tile is a little thicker than the others so appears more opaque.

    IMG_6438

  • Techniques

    Omega HH506RA Pyrometer

    In the future I’ll be adding articles to this website.  The first article that came to mind was a review of an excellent pyrometer I recently purchased, the Omega HH506RA.

    Omega HH506RA Dual Input, High Accuracy Datalogger/Thermometer ($199USD)

    I was looking for a thermometer to use primarily with my gas kiln, preferably a portable version that i could easily detach and use with other kilns in my workshop.

    My main requirements were:

    • At least two inputs for the two thermocouples (top & bottom) in my gas kiln.
    • Multiple thermocouple types.  I fire the gas kiln to cone 9-12 so prefer S-type thermocouples for their greater accuracy (0 to 1600°C continuous temperature range) and longevity.  But for my cheap bisque electric kiln I use K-type thermocouples (0 to +1100°C).
    • Real-time datalogging using a serial or USB cable which can be connected to a computer.  Ideally, the data should be transmitted in a non-propriety format which can be read directly from the port or from a simple text file.  (Logging is important as I’m also helping a ceramicist friend who wants to view firing data from his kilns while he’s out of town.)
    • Dual voltage, or preferably battery operated.
    • Rugged housing, solid build quality.

    Fluke offers the Series II Model 52 which has two inputs and datalogging.  However, from reading the manual it seems that the data can only be viewed on the computer through Fluke’s proprietary FlukeView Forms software, adding at least another hundred dollars (for the basic version) to the over $300USD cost of the thermometer.

    After looking through the Clayart mailing list archives I started looking into Omega thermometers.  Omega’s website (www.omega.com) can be quite confusing due to the abundance of options available, but after much searching it seemed that the Omega HH506RA would meet all my requirements.  A quick response from Omega support confirmed everything I needed to get things working.

    • Omega HH506RA Thermometer ($199) 2-Channel Temperature Measuring, 7 Thermocouple Types , Triple Display with Setable Backlight , Triple Display with Setable Backlight , Save Data (128 Samples with Real-Time Data), Datalogging (16 Sets, Max 1024 Data Capacity), Time, Record Interval, APO Time Setting , Software Package Included (RS232C Cable and Disk, Model HH506RA Only), °C/°F Switchable , 0.1 Resolution , Water/Splash Resistant, NEMA-4X,, Dustproof
    • Accessory HH506RA-USB-SW ($30) USB cable and software for Win98/NT/2000. The HH506RA already comes with software and a RS232 cable.  But a lot of computers don’t even have RS232 ports anymore, so I added the USB cable.
    • Miniature Thermocouple Connectors Flat Pin  (Part number SMPW-K-M for K-type, SMPW-R/S-MF for S-type.) You will need one male connector for each type of themocouple you’ll be using.  The connectors are easily be attached to the ends of thermocouple wires and then plugged into the thermometer.  I purchased two S-type connectors for the gas kiln and two K-type connectors for the electric bisque kiln.
    • R and S Type Thermocouple Extension Wire  I already had thermocouples and wire.  But if you need to purchase the wire, Omega sells it in a minimum of 25′ rolls.  Part number EXTT-RS-20-25.

    Installation

    As I mentioned, I already had thermocouples and wire.  So all I had to do was attach the thermocouple wires to the Omega connectors and then insert into the thermometer.  I was concerned that simply adding the Omega connectors and thermometer would lead to accuracy problems due to the length and gauge of the wire not being matched to the thermometer.  After many tests against my old pyrometer and cone firings, I was happy to find that the Omega is very accurate.

    As you can see in the above picture, my thermocouple wires are thick-gauge, much thicker than the Omega connectors are designed to be used with.  But they work together just fine, even though the connector covers cannot be used.  Thermocouple inputs and USB/RS232 input are all located at the top of the unit.  The display is quite clear and has an illuminated display.  Thermometer controls are fairly easy to figure out.  You need to adjust the settings to match your setup.  As you can see in the display, the current reading is 9°CS, C representing Celsius and S representing the type of thermocouple.  Mismatching the thermocouple type with thermometer settings will give incorrect readings.

    Output from the HH506RA using the Omega software

    The USB cable is easily connected to a computer.  The Windows software is quite old but simple to install and run.  The dual temperature displays and temperature difference display are very nice, but unfortunately I’ve found the graphing function unusable.  Fortunately, the simple tab-delimited text file output of the Omega software is easily imported into spreadsheet applications like Excel and Google Docs.

    Using Excel with Omega temperature output

    The Omega temperature output file as viewed in Excel and simple text (above).

    Using Google Docs

    Below, the file after being uploaded to Google Docs and viewed in a simple Line Chart.  The same could be done in Excel.
    By the way, the above graph shows my firing schedule.  This instance isn’t a particularly good firing.  Slow rise first hour to get rid of moisture, fairly fast to 800, from 800-900°C soak with slight pressure for a couple hours until kiln evens out, begin reduction just after with gradual decrease as reaching temperature, soak for another hour until Chinese cone 9 drops (about 1310°C), crash cool with full open damper until 900°C.  It’s a ten (in this case, twelve) hour firing but doesn’t take a lot of gas due to the three or more hours of relaxed soaking.

    Conclusion

    At $199USD the Omega HH506RA thermometer is an excellent value.  I’ve already used it for a year and haven’t had any problems.  It’s built solidly and the original 9v battery hasn’t died yet.  I really like the display on the computer monitor, especially the difference between the two thermocouple readings.  It would be nice if Omega had better software for looking at graphs, but since the files are easily imported into Excel this isn’t much of an issue.
  • Craft

    纪录片《china-瓷》

    It’s said that you can tell how long a foreigner has been in China by the number of appearances they have on Chinese television.  I’m not doing well, I guess, because I’ve only been in one documentary.

    “China · porcelain” is a documentary about the fascinating history of Chinese export porcelain in the Ming and Qing dynasties, including Chinese porcelain’s influence on world trade, culture, and the economy.
  • Glazes

    The Glaze Sprayer Maker

    Some of the tinsmith's tools

    Templates for glaze canisters

    Each type of glaze canister has a specific application, from spraying large sculptures to detailed underglaze application.

  • Techniques

    New kiln

    Steel-frame fiber propane gas kiln, six venturi burners, single shelf (64x64cm).

    Steel frame of gas kiln in progress

    Steel frame of gas kiln in progress

    Steel frame of gas kiln

    Steel frame of gas kiln

    Completed gas kiln with steel frame and stainless steel panels

    Completed gas kiln with steel frame and stainless steel panels

    Inside of completed gas kiln

    Inside of completed gas kiln