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Clay and Glaze Materials:           The earth is composed of about 68% silica. Most of the natural minerals that are mined are some form of silicate rock. The ancient potters gathered rocks and clays and made ashes from organic material to make their glazes. The glaze materials that we potters use, come from mining operations for gold and silver and copper and agregates for the building and paint industry. They are the by product of these operations. When a mine becomes unprofitable to operate, we can no longer get that material. Sometimes we have to take several materials and attempt to make the best formula we can. There are forumlas for 'theoretical equivelants' for many materials including feldspars, clays, and stones. Unfortuately, we deal in reality and there is no such thing as an exact 'theoretical equivalent. What we do is make a new and different glaze that uses a similar composition to an old glaze. It is like making "Italian Pizza " or " Chop Suey " there really is no such thing, but there is a "Chicago Style Pizza " and also, a " San Francisco Chop Suey " . In a similar way there is a Chun Glaze that I make from American materials that looks like the ancient Chinese Glaze. I use Custer Feldspar, which is much different than the Feldspar that the Sung dynasty potters used. The Gerstley Borate is a Substitute for Colemanite, but it is much different than Colemanite and have to adjust my glazes for it. I may balance the acid and base elements of a glaze, like the Chinese did, but its really a different glaze.
          I group glaze materials into eight general groups. The Feldspars, the Clays, the Modifyiers, the Ashes, the Metallic oxides, the synthetic stains , the lead Frits and Quartz.

I.The Feldspars
          The first group include the Feldspares and minerals that act like feldspars in a glaze at the appropriate temperatures. These are all naturally mined and milled minerals:

Custer Feldspar (69)K3O (31)Na3O Al2O3 7SiO2
Kona F-4 Feldspar (32)K2O (48)Na2 O (20)CaO Al2 O3 7SiO2
Oxford Feldspar (32)K2 O (48)Na2O (20)CaO Al2O3 7SiO2
Kingman Feldspar (70)K2O (31)Na2O (5) CaO Al2O3 6SiO2
Cornwall Stone (356) K2O (340)Na2O (304) CaO Al2O3 8SiO2
Nephalyne Syenite (25) K2O (75)Na2O Al2O3 5SiO2
Spodumene Li2O Al2O3 4SiO2

          The Feldspars contain Potassium, Aluminia, Silica, and Sodium in differnet amounts. Feldspars act as a flux to melt the silica into a licquid glass. This is caused by the high amounts of Potassium in the pot ash feldspar, Sodium in the Soda ash Feldspars and Lithium in Spodumene. Additionally, there are several trace elements in these congolomerate mineral. These trace elements make up another major difference between the different forms of Feldspars. Traces of Iron and Mangonese are common. Additonally, Spodumene and Lepidolite contain Lithium, in high consontrations, which acts in the same manner as Potassium and fluxes the silica into a glass at lower temperatures of between 2000 (F) and 2800 (F). Nephalyne Syenite contains large amounts of Sodium. Feldspars are the ideal material for glazes in the High Fire range of cone 9 to 14. Glazes can be made from just Feldspar alone at these temperatures, although they tend to craze and form a milky opalescent opaque glass. Simple glazes can be made from clay and feldspar in a 50:50 ratio.

II.The Clays

          The Clays form the next group of material. There are several clays that I use in glazes:
China Clay or EPK supplies Silica and Alumina in my glazes. It is composed of
The most important thing about China Clay is that it contains no other minerals and in particular, no Iron.
Om4 or Kentucky Ball Clay
has about the same formula as China Clay, Albany Slip Clay
is a naturally occuring clay that has a higher iron oxide and Titanium in its composition. This will form a dark glaze when applied on the surface of a pot by itself. When another glaze is applied over it, a mottled effect occures. Often this clay is used as a slip glaze to make single fired pottery.
Red Mule orK-Red
is an iron bearing ball clay that can be used to color the stoneware clay or make an excellant slip glaze.

III.The Modifiers:

          The next group, I call the modifies. All of these materials modify the glaze to some degree. They are usually about 10 to 20 percent of the glaze. They cause the glaze to have a certain quality by the addition of an element. This group is composed of :

Dolomite CaCO3 MgCO3
Is a source of Magnesium in the glaze. This promotes matt glazes. By carefully additing just the right amount of Dolomite to a clear glaze, I produce a glaze that is partly matt and partly shiney.

Gerstley Borate 2CaCO 3B2O35H2O it is a source of Boron and Calcium in an insoluable form. That is it does not disolve into the water as much as Borax does.Its use brightens the glazes.

Borax 2Na2O 2B2O210H2O
Supplies Boron in a soluable form. I find that there is enough Boron an other minerals supplied to make this a much needed material when making glazes that call for Boron than just using Gertley Borate. I use Borax in my glazes a lot.

Barium Carbonate BaCO3
Is a source of Barium in the glaze and promotes very bright colors. I use it in the Chun and copper red glazes. It is poisonous and you should not handle food or cigarettes around it.

Talc 3MgO 4SiO2 H2O The primary purpose of Talc is to flux the glaze and give it strength. Talc adds both Magnesiumand Calcium to a Glaze.

Whitting CaCO3 Whitting is used as a flux. It is the best replacement for Leads in the glaze because it is food safe. Calcium Carbonate will cause bubbling in the glaze mix and you need to add a gas hungry substance like Zinc to promote healing the glaze. In the reduction firing, a slow oxidaition soak on low will help take care of pinholing due to the release of the carbonate radical during glaze formation.

VI.The Ashes:

Wood Ash
          The Ashes are part of the modifier family of materials that have their own group because they are a very special ingredient and do wonderous things for the Glazes. Wood and plant ashes vary in composition greatly. Each batch of ash will have its own characteristic formula. This can be true even though you use the same type of tree from the same forest or the same plants. The reasons for this have to do with soil contitions and the way the ashes were burned and how much were washed. All we can say about the formula they of a wood ash is that it is 'theorietically':

Silica 20% to 50% SiO2
Alumina10% to 15% Al2O3
Lime or Dolomite5% to 30% CaCO3
Potasium5% to 30% K2CO3

With trace elements of iron, manganese, Phosphorous, magnesia, and others

Bone Ash Ca2(PO4)2 (Calcium triphosphate) This material is responsible for the Legend that I retell as 'The making of the Holy Grail'. It is the essential ingrediant for making Iron glazes turn from black to red.
Rice Hull Ash
The theoretical composition of Rice hull ash depends upon the manufacturer. It is very difficult to say what the composition of these organic materials are. Much of their compostion is determined by how they are washed.

V.The Metallic Oxides

The metallic oxides act mainly as colorants in the Glaze.
Red Iron Oxide Fe2O3
makes black glazes and red glazes. 1% to 5%
Black Iron Oxide FeO
makes black glazes and red glazes. 1% to 5%
Cobalt Carbonate CoCaO3
is used to make a deep blue 1 to 3%
Black Cobalt Oxide Co3O4
much stronger to make blue with 1%
Copper Carbonate CuCO3
Used to make a greens, reds, blues 2%
Rutile TiO2
Used to make a mottled look. Colorants for Blues with Copper and browns with a high alumina content.10%
Manganese Dioxide MnO 2
Makes black glazes blacker and blue glazes bluer 3% It is also used in Luster glazes for the metal look
Tin SnO3 makes whites whiter and promotes copper red 1to 10%
Chroium Carbonate
Makes a chrom green. Good for decoration 3%
Lithium Carbonate LiCO3
Used to add Lithium to a glaze in replace of Spodumene.
A feldspar plus Lithium will be the equivent of Spodumene.

VI.Commerciall Prepared Stains:

          There are a number of commercially prepaired stains that derive their color from new space age colorants for high temperature. I am not sure what they are really made out of, as their forumlas are a secret. They are some kind of space age heat resistent plastic. There are also a number of commercially prepaired Tin Vanadium stains of various color.

VII.The Lead Fritz

          The lead Fritz are used in some Raku Glazes. I dont use these materials. Many of them are safe for funtional food ware, but I have choosen not to use them in making my pottery. Part of the reason for this is the high temperatures that I fire at make them unreliable for my glazes. I havve found better materials to flux the glaze and keep other metals in the glaze suspension from boiling out.

VIII.Silica or Quartz

          Last but not least is the main ingredient to all glazes, Flint or Silica Dioxide. SiO2 Quartz melts at about 4400 degrees F. It needs to be fluxed down inorder to be used in Pottery. There are several grades and two kinds of Silica. I use a 200 mesh silica for my glazes. This fits my clay body best and does not settle out in the glaze as quickly as the higher 320 mesh Silica. There are Hydrous and Anhydrous silicas. Ground Flint is a Hydrous silica. For an interesting effect, you can try an anhydrous silica, like bottle glass in the bottom of a small bowl or teacup. This kind of silica will crack and craze when cooling for a beautiful effect that is technically a glaze flaw.

Glaze Formulas

          Glaze Recipies       My Glaze formulas are based upon the glazes that I have used from several studios and the books of Daniel Rhodes, Glenn Nelson, Dick Berhens, Tom Frazier, Michael Cardue, Bernard Leach and a host of others. I fire them in my kiln in my way. I have modified them for use with heat to cone 13 and strong reduction.

         I use my methods of glazing. It is very important
to understand this concept for the potter. Its 
your glaze ; you are just using the recipie. 
You must learn to make the glaze your own. 
These reciepies are to make 5 gallons 
of glaze. Some of the specialty glazes are 
made in one quart bactches. I divide the large
batches by 10 and multiply by 2. If you are making
smaller quanities,  you may want to divide  
the batches by 20.

      I.Iron Red
      This is an iron saturate glaze. Its the first glaze that I learned to use. I have modified the glaze for my own use in my kiln for a hotter temperature. Its a beautiful Iron red glaze. I use it with Cindy Yellow for a mottledlook. Dinner ware on a wood table with these glazes is attractive.
          Feldspar 5400 grams
          Whitting 800
          Flint 2400
          EPK 700
          Talc 700
          Bone Ash 1100
          Red Iron Oxide 1200

     This a beautiful black glaze that I use in combination with the Chun series of glazes and Teadust. I call my combination Starry Night
          Feldspar 4480 grams
          Whitting 1200
          Flint 1600
          OM4or K ball 600
          Red Iron Oxide 640
          Bentonite 160

      III.Cindy Yellow or Rhodes 32 (with Rutile)
      This is a high alumina matt glaze with rutile for coloring. It has a beautiful matt finish. When Iron Red is applied over or under it, I have a very nice glaze. The way I make the glaze, I need high heat to achieve its best colors.
          Feldspar 3000 grams
          Whitting 300
          Dolomite 1650
          EPK 1875
          Rutile 201
for a variation to this, I add 200 grams of Spodumene
and subtract 100 grams of Whitting.

      IV. PK White is an opalescent white glaze.
It is a shine that I like to use with my other glazes.
I use it as a base coat with the Chun and Teadust
glazes over it.

          Nephalyne Syenite 3520 grams
          Whitting 400
          Flint 1600
          EPK 800
          Talc 1200
          Gerstley Borate 1040
          Spodumene 160
          Zircopax 400

      V.Shanner Series of Glazes
      These are glazes based on Dick Shanner's reciepies. I use the matt blue glaze for a glaze with a long firing range. It works well at cone 9 and does not run at cone 13 when applied thinly. I use it in combination with my Chun series of glazes.

          Feldspar 5270 grams
          Whitting 2130
          Flint 2400
          EPK 2500
          Talc 400
          Bone Ash 300
          Cobalt Oxide 55 grams
          Rutile 110
          Red Iron Oxide 110
          Rutile 440 grams
          Red Iron Oxide 400
          Zircopax 440 grams
          Rutile 440 grams
          Green Chrome Oxide 400

      VI. Chun Series of Glazes
          These are glazes based on the ancient Chinese reciepies for a Chun Glaze. The addition of Whitting to the glaze is obviously an attempt to adjust the glaze for a lack of calcium in the original feldspar. As is the additon of EPK to add Alumina. This glaze works very well. It is my most important glaze to use over other glazes. It runs a lot. I never use this glaze as a base coat. It works over other glazes.

          Feldspar 2880 grams
          Whitting 180
          Flint 1800
          EPK 50
          Gerstley Borate 600
          Zinc Oxide 120
          Barium Carbonate 300
          Dolomite 600
          Zircopax or Tin 180
      Mottle Blue:
          Rutile 340 grams
          Copper Carbonate 34
      Copper Red: (Use tin)
          Copper Carbonate 100 grams
          Silicon Carbide FFF 50
          Red Iron Oxide 120 grams

      V. Boron Clear
      Boron Clear is a beautiful Crackle glaze. I use it on White stoneware and Porcelan Clay. If you play with the amounts of silica in the glaze, you will achieve different crackles. By adding 5% Silica, you can eliminate the crackle. I use the Chun and Copper Red Glazes over this Glaze.

          Feldspar 3140 grams
          Whitting 1236
          Flint 1820
          EPK 876
          Gerstley Borate 925

      VII.Russell's Copper Red Glaze.
      This is a glaze I finally worked out to make a Copper Red that would work at Cone 11 and 12. I use it over the Boron Clear Glaze. The Boron Clear serves to catch the runny copper Red Glaze. It is a deep copper red when I reduce the kiln correctly.

          Nephaline Syenite 3520 grams
          Whitting 400
          Flint 1600
          EPK 800
          Talc 1200
          Bone Ash 400
          Gerstley Borate 1040
          Borax 400
          Zinc Oxide 300
          Silicon Carbide fff 80
          Copper Carbonate 120
          Tin Oxide 320
          Iron Oxide 80

      VIII.Russell's Chun Red
      My Chun Red is actually a light pink and can be bubbly if fired under cone 10. I place it in the hottest part of my kiln. I use this over several other glazes. It is a top layer. I vary the composition of this glaze greatly when I mix it up. I use it to surprise me.

          Feldspar 1440 grams
          Whitting 90
          Flint 900
          EPK 90
          Gerstley Borate 300
          Bone Ash 300
          Borax 300
          Zinc Oxide 60
          Dolomite 300
          Barium Carbonate 150
          Red Iron Oxide 17
          Silicon Carbide fff 17
          Copper Carbonate 30
          Manganese Dioxide 20 grams
          Nickle Oxide 10

      IX. Teadust Glaze
      The glaze is composed to go from matt to shiney. The Dolomite crystals float thru the glaze. I use this on top of another glaze. I have modified my version with the additions of cobalt and manganese dioxide. The original reciepe called for Kingman Feldspar and so I have added extra Calcium to the Glaze in the form of more whitting.
          Feldspar 1220 grams
          Whitting 320
          Flint 550
          EPK 250
          Gerstley Borate 80
          Bone Ash 300
          Borax 300
          Red Iron Oxide 25
      #1 Blue:
          Cobalt Carbonate 30 grams
          Manganese Dioxide 20
      #2 Green:
          Nickle Oxide 10 grams
      #3 Green:
          Green Chrome Oxide 10 grams

      X. Decorative Stains.
      I use commercially available stains for Figurative decoration. I prepair these stains with several additions.

      A1 Blue Stain
          Feldspar 10 grams
          EPK 10
          Cobalt Carbonate 5
      B1 Blue Green Stain
          Feldspar 40 grams
          EPK 30
          Blue Green Stain 20
      C1Brown Stain
          Feldspar 10 grams
          EPK 20
          Iron Oxide 5
          Chrome Oxide 2

      X. Luster Glazes.
      I am attempting to experiment with making High fire in glaze lusters. These are coatings of luster metallics that I apply on top of my glazes. So far, I have some intereting results. The metallic lusters give the glazes even more pazaz. They are rare at the temperatures that I fire at. The metals run and bubble quite a bit. Some modifications will be nesicary for any of these to work at the temperatures I work at.

      Variation #1
          Neph Syenite 225 grams
          Whitting 65
          Flint 70
          OM4 30
          Copper Carbonate 30
          Red Iron Oxide 5
      Variation #2
          Neph Syenite 290 grams
          Whitting 18
          Flint 180
          Gerstley Borate 60
          Zinc Oxide 12
          Barium Carbonate 30
          Dolomite 60
          Chrome Oxide 30
          Manganese Dioxide 5

      Variation #3
          Feldspar 150 grams
          Whitting 10
          Flint 90
          Gerstley Borate 30
          Zinc Oxide 6
          Barium Carbonate 30
          Dolomite 30
          Nickel Oxide 30
          Red Iron Oxide 5

      X. Clay Bodies
      There are two clay basic clay body reciepies that I use to make my pottery out of. The first is a Stoneware body. I use materials from Industrial minerals to make it. These are local California Clays that are inexpensive. I age the clay for at least 3 weeks. Some of the clay is aged for 6 months to make the larger forms. Aging and adding vinigar help make the clay more plastic and give it strength. I mix my clay in an old ships' dough mixer. I can mix about 300 lbs of clay at a time. I include about 6 to eitht pails of slip clay reconstituted from scrap clay soaked in large plastic garbage cans:

          Immco 400 (Fire Clay) 50 pounds (lbs)
          49er Ball Clay (Ball Clay) 50 lbs
          Immco 800 (Iron bearing Fire Clay) 25 lbs
          Red Mule (Iron bearing Ball Clay) 6 lbs
          Feldspar 10 lbs
          Sand 60 mesh 10 lbs
          Bentonite 5 lbs
          Vinigar one cup in a 5 gallon bucket of water

      White Stoneware or Porcelean Clay:

          6-Tile Clay 50 lbs
          EPK 25 lbs
          Silica 25 lbs
          Feldspar 40 lbs
          Bentonite 5 lbs
          412 Ione Grog 8 lbs
          Vinigar one cup in a 5 gallon bucket of water

      The grog makes this formula technically a white stoneware. Wtihout the grog, the clay is fairly hard to throw without cracking in the drying process. I make teapots and platters and large vases from this clay body.

      For more information on Glaze Materials: Go to Leslie Ceramics website and look at their catalogue page: Leslie Ceramics
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