Clay and Glaze Materials

Clay and Glaze Materials:

The earth is composed f 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 di erent 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 di erent than the Feldspar that the Sung dynasty potters used. The Gerstley Borate is a Substitute for Colemanite, but it is much di erent 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 di erent 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 di ernet 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 di erence between the di erent 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 Al2O32SiO2H2O. 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 e ect occures. O en this clay is used as a slip glaze to make single fired pottery. Red MuleorK-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 : DolomiteCaCO3 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 CarbonateBaCO3

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. WhittingCaCO3

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

mina10% 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 di icult 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 OxideFe2O3 makes black glazes and red glazes. 1% to 5% Black Iron OxideFeO makes black glazes and red glazes. 1% to 5% Cobalt CarbonateCoCaO3 is used to make a deep blue 1 to 3% Black Cobalt OxideCo3O4 much stronger to make blue with 1% Copper CarbonateCuCO3 Used to make a greens, reds, blues 2% RutileTiO2 Used to make a mottled look. Colorants for Blues with Copper and browns with a high alumina content.10% Manganese DioxideMnO2

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 e ect, 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 e ect 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

II.Temoku 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.NephalyneSyenite

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 --------------------------------------------------------------------Blue: Cobalt Oxide 55 grams Rutile 110 Red Iron Oxide 110 --------------------------------------------------------------------Orange: Rutile 440 grams Red Iron Oxide 400 --------------------------------------------------------------------White:Zircopax 440 grams --------------------------------------------------------------------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 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 --------------------------------------------------------------------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 di erent 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 f 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 f 17 Copper Carbonate 30 ---------------------------------------------------------------------

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 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 ---------------------------------------------------------------

Variations: #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:

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