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 materialto make their glazes. The glaze materials that we potters use, come from miningoperations for gold and silver and copper andagregates 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 thingas an exact 'theoretical equivalent. What we do is make a new and different glazethat 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 thatI make from American materials that looks

like the ancient Chinese Glaze. I useCuster Feldspar, which is much different than the Feldspar that the Sung dynastypotters used. The Gerstley Borateis 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 theChinese 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 glazeat 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. Feldsparsact 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 Mangoneseare common. Additonally, Spodumene and Lepidolite contain Lithium, in high consontrations, which acts in the same manner as Potassium and fluxesthe silica into a glass at lower temperatures of between 2000 (F) and 2800 (F). Nephalyne Syenite contains large amounts of Sodium. Feldspars arethe ideal material for glazes in the High Fire range of cone 9 to 14. Glazes can be made from justFeldspar alone at these temperatures, althoughthey 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

Al2O32SiO2H2O.

The most important thing about China Clay is that it contains no other minerals andin 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 Titaniumin 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 mottledeffect occures. Often this clay is used as a slip glaze to make single fired pottery.

Red Mule orK-Red

is an iron bearing ball claythat 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 somedegree. They are usually about 10 to 20 percentof the glaze. They cause the glaze tohave 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. Thispromotes matt glazes. By carefully additingjust the right amount of Dolomite to a clearglaze, I produce a glaze that is partly mattand partly shiney.

Gerstley Borate 2CaCO 3B2O35H2O it is a source of Boron and Calcium in an insoluableform. That is it does not disolve into thewater as much as Borax does.Its usebrightens 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 replacementfor Leads in the glaze because it is food safe. Calcium Carbonate will cause bubbling inthe 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 takecare of pinholing due to the release of thecarbonate radical during glaze formation.

VI.The Ashes:

Wood Ash

          The Ashes are part of the modifier family of materials that have their own groupbecause they are a very special ingredientand do wonderous things for the Glazes. Wood and plant ashes vary in compositiongreatly. Each batch of ash will have its own characteristic formula. This can be true even though you use the same typeof tree from the same forest or the same plants. The reasons for this haveto do with soil contitions and the way the ashes were burned and how much were washed. All we can say about the formulathey 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 agecolorants for high temperature. I am not sure whatthey are really made out of, as their forumlasare a secret. They are some kind of space age heat resistent plastic. There are also a numberof 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 themare 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 higher320 mesh Silica. There are Hydrous and Anhydrous silicas. Ground Flint is a Hydrous silica. For an interesting effect, you can tryan anhydrous silica, like bottle glass in thebottom of a small bowl or teacup. This kind of silica will crack and craze when cooling for abeautiful 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 ofDaniel 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 importantto 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 largebatches by 10 and multiply by 2. If you are makingsmaller 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 formy own use in my kiln for a hotter temperature.Its a beautiful Iron red glaze. I use it with Cindy Yellowfor 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

      II.Temoku      This a beautiful black glaze that I use incombination with the Chun series of glazesand 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 isapplied over or under it, I have a very nice glaze. The

way I make the glaze, I need high heat to achieveits 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 longfiring range. It works well at cone 9and 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

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      Blue:

          Cobalt Oxide 55 grams

          Rutile 110

          Red Iron Oxide 110

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      Orange:

          Rutile 440 grams

          Red Iron Oxide 400

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      White:

          Zircopax 440 grams

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      Green:

          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 Whittingto the glaze is obviously an attempt to adjustthe 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 thisglaze 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

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      Mottle Blue:

          Rutile 340 grams

          Copper Carbonate 34

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      Copper Red: (Use tin)

          Copper Carbonate 100 grams

          Silicon Carbide FFF 50

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      Celedon:

          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. Byadding 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 therunny 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 firedunder 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

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      Variations:

          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 calledfor Kingman Feldspar and so I have added extra Calciumto 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

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      Variations:

      #1 Blue:

          Cobalt Carbonate 30 grams

          Manganese Dioxide 20

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      #2 Green:

          Nickle Oxide 10 grams

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      #3 Green:

          Green Chrome Oxide 10 grams

      X. Decorative Stains.

      I use commercially available stains forFigurative decoration. I prepair thesestains with several additions.

      A1 Blue Stain

          Feldspar 10 grams

          EPK 10

          Cobalt Carbonate 5

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      B1 Blue Green Stain

          Feldspar 40 grams

          EPK

30

          Blue Green Stain 20

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      C1Brown Stain

          Feldspar 10 grams

          EPK 20

          Iron Oxide 5

          Chrome Oxide 2

      X. Luster Glazes.

      I am attempting to experiment with makingHigh fire in glaze lusters. These are coatingsof 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 quitea bit. Some modifications will be nesicary for anyof 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

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      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

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      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 clayreconstituted from scrap clay soaked in large plastic garbage cans:

      Stoneware:

          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 There are lots more links on my links page: Links Page