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MATERIAL DESCRIPTIONS AND SAFETY DATA

#6 TILE CLAY:  An air-floated kaolin with bright firing properties yet highly plastic.  It offers high green strength for superior jiggering and wet processing properties.  ​
ALBERTA SLIP:  A manufactured slip produced by the Archie Bray Foundation that is designed to duplicate the chemical and physical properties of Albany Slip.  As a glaze it produces rich yellows, blacks and browns over a wide range of temperatures (2012° F to 2372° F).  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
ALUMINA HYDRATE: (Al2O3·3H2O):   A fine granular white powder that has a very high melting point and is sometimes used as a source of alumina in glazes.  Stays in glaze suspensions well and can improve glaze adhesion.  Large quantities in glazes can cause gas bubbles to form creating opaque matte surfaces.  Acute effect: Mild irritant.  Chronic effect:  May be hazardous over long term.
ALUMINA OXIDE: (Al2O3):   Calcined (heated) alumina.  Second hardest substance on earth and in ceramics second only to silica in importance.  Insoluble in water and acts as a stabilizer and hardener in glazes.  Pure alumina oxide is rarely used in glazes as sufficient quantities are found in kaolin and feldspars.  Acute effect: Mild irritant.  Chronic effect:  Hazardous over long term.
BARIUM CARBONATE: (BaCO3)   A dense white powder used in barium crystal matte glazes and as an anti-scumming agent in clay bodies that contain soluble salts.  Controversy exists surrounding its toxicity in ceramics.  Most MSDS listings have it as an insoluble material that is non-toxic to skin contact, mildly toxic by inhalation and the amount used in clay bodies make ingestion toxicity next to impossible.  Silica has a much higher hazard rating than barium.    Acute effect:  Mild irritant in skin contact, moderately toxic in ingestion.  Chronic effect:  None reported
BENTONITE:  Extremely plastic clay formed from decomposed volcanic ash.  Used to add plasticity to clays and to keep glazes in suspension.  Up to 2% can be added to clay bodies and up to 1% in glazes with few adverse effects. Most bentonites swell (some up to 15 times their size) when added to water. Acute effect: Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
BONE ASH: (3CaO·P2O5)  Ground calcined bones used in clay bodies as a flux and in glazes as an opacifier.  Helps tin oxide in glazes but can be a cause of crawling and blistering.  Synthetic version is tri-calcium phosphate.  Acute effect:  Mild irritant.  Chronic effect:  None reported.
BORAX: (Na2O·B2O3)  Made from the mineral tincal, found in the Mohave Desert, Borax is used to make low-melt glaze frits without the use of lead oxides. It is the main source of boron oxide in glazes which acts as a flux and glass forming agent at nearly all temperature ranges.  Acute effect:  Mild irritant.  Chronic effect:  Mild irritant.
C & C BALL CLAY:  A highly plastic, light colored secondary (sedimentary) clay that vitrifies in the 2012° F to 2192° F range.  Sometimes called blue or black clay depending on the amount of organic material present.  Used to add plasticity to throwing clay and fluidity & green strength to casting slips.  If used in high percentages excessive shrinkage may occur.  The term ‘ball’ clay comes from the old hand mining technique where small blocks were cut from deposits,  the corners of which would get knocked off during handling and storage, leaving roundish balls of clay.  Acute effect: Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis
CALCIUM CARBONATE: (CaCO3)  Used to introduce calcium oxide into glazes and clay bodies.  It is a filler and opacifier in low fire clays and glazes and a flux in high temperature glazes.  Also called carbonate of lime, whiting, limestone, marble dust and chalk.  Acute effect:  None reported.  Chronic effect:  May be hazardous over long term.
CHROME OXIDE: (Cr2O3)  Used as a glaze colorant to produce greens and sometimes reds under special conditions.  Typically used in temperatures under 2150°F.  Chromium oxide glazes may look different in natural light versus artificial light.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term.
COBALT CARBONATE: (CoCO3)  A strong colorant used to produce blues in glazes, slips and clay bodies.  Carbonate form is only 65% as effective as the oxide, but produces softer more evenly distributed color making it easier to control in glazes. Co contents vary by grade and manufacturer so test when switching cobalt suppliers.  Cobalts of the same concentrations may differ in color in the raw state but should fire the same.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term.
COBALT OXIDE: (Co3O4)  The most powerful ceramic colorant, cobalt oxide is a general term for a group of cobalt and oxygen containing compounds that have been used for nearly 2000 years.  It is not affected by reduction or oxidation and is stable at almost all ceramic temperature ranges.  Less than 1% is enough for strong blues.  Due to its dense concentrated nature, if it is not sieved or ball milled it can cause severe speckling and spotting.  Acute effect:  Mild irritant.   Chronic effect:  May be hazardous over long term.
COPPER CARBONATE: (CuCO3)  A useful source of copper oxide for staining glazes and clays. Copper carb. contains less copper than its oxide form making it easier to disperse in mixtures, produces lighter color ranges and is ideal for brush decoration as it melts better reducing oxide speckling.  Large concentrations may produce pin holing and blistering.  Copper carb. in its raw form may vary in color and density but the amount of copper present stays fairly constant.  To convert copper oxide to copper carb. in a recipe, multiply the oxide amount by 1.55.  Acute effect:  Irritant.  Chronic effect:  May be hazardous over long term.
COPPER OXIDE, BLACK: (CuO)  One of the oldest colorants used in ceramics, copper oxide is a strong flux and yields green colors in amounts below 5% and blacks in amounts above 5%.  Reds are possible in reduction firings.  Copper oxide does not disperse well in glazes and may cause speckling.  When used in clay bodies the color results will vary depending on the amount of body vitrification. (copper filings added to clay will give strong copper spotting)  Acute effect:  Irritant, may be hazardous.  Chronic effect:  May be hazardous over long term.
CORNWALL STONE: Cornwall stone is a low iron feldspar material used primarily as a flux in clay bodies and glazes. Is mined in the Cornwall area of the UK. It melts 1150-1300C. It has a more diversified selection of fluxes than other feldspars but also has one of the highest silica contents. By itself it does not melt as well as feldspars (melt flow begins around cone 11 oxidation). It is popular in engobes for its adhesive power during and after firing and in glazes for its low shrinkage and minimal contribution to defects. 
CRYOLITE: (Na3AlF6)  A natural mineral associated with granites, composed of fluoride, aluminum and sodium.  Used in the production of crater glazes and helps produce crackle effects in alkaline glazes.  Acute effect: Mild irritant.  Chronic effect: May be hazardous over long term.
DOLOMITE: (CaMg(CO3)2)  Dolomite limestone, a double carbonate of calcium and magnesium in crystalline form.  Used to introduce calcium and magnesium oxides into glaze formulas.  It is a high temperature flux and large quantities are used in the formation of crystalline effect glazes.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term.
E.P. KAOLIN (Edgar Plastic Kaolin / E.P.K.):   A primary clay with moderate plasticity that is prized for low iron content which imparts a very clean white color.  Sometimes called china clay, kaolin is used as a prime source for Alumina Oxide and Silica in glazes. Due to its high Aluminum Oxide content, kaolin is a refractory with a melting point over 3218° F.  E.P. Kaolin is mined in Edgar Florida and chemically is very close to the theoretical kaolin make up, making it a good substitute for other kaolin’s with similar properties. Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
FELDSPAR, CUSTER: (Potash)  A ceramic grade high potash feldspar used by a majority of the ceramic industry.  There are twelve true feldspars and many, many other feldspathic materials called feldspathoids.  Up to 25 % is used as a body flux in clay bodies and up to 100% can be used in glazes.  Feldspars are a valuable means of introducing alkalis into a body or glaze.  Potash is the most common type of feldspar, so much so that if no other type is indicated it can be assumed potash is called for.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term.
FELDSPAR, MINSPAR 200: (Soda)  Soda feldspars, the second most common form of feldspar, are used as a body flux and in glazes they provide silicates.  Slightly different color developments will occur if sodium feldspars are used in place of potash ones due to the difference in alkaline properties.  Sodium feldspars have a high coefficient of expansion and glazes that contain them are more likely to craze.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term.
FLOURSPAR: (CaF2)  Sometimes called calcium fluoride, fluorite and blue john; fluorspar is used in the formulation of frits, as a low fire opacifier in enamels and in special effect crater glazes.  Fluorine gas, a health hazard, is a by product when fired to high temperatures.  Cornish stones may contain up to 2% fluorspar and can cause damage to kilns, windows and the lining of lungs unless venting is addressed.   Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term.
GERSTLEY BORATE:  A complex calcium borate composed of colemanite (a calcium borate), ulexite (a sodium calcium borate), shale (a clay/feldspar) and limestone (calcium carbonate).  Gerstley is a powerful flux used as a lead replacement for temperature ranges below 2000°F.  The Gerstley Borate mine was closed in 2000 and while the mine is no longer actively producing, Laguna Clay Co. predicts that the stock pile of crude GB will last another 8 to 10 years (from 2006) if current levels of usage stay the same.  Acute effect:  Mild irritant.  Chronic effect:  None reported.
GOLD ART CLAY:   A plastic stoneware clay mined in Southern Ohio by Cedar Heights.  A very versatile clay that can be used alone or as a ball or fire clay in clay and glaze mixes.  It fires to a light golden buff color, is an air floated 200 mesh particle size and fires from cone 06 -12.  Can be used as a substitute for Jordan Fireclay. Acute Affect: Mild irritant.   Chronic effect:  May be hazardous over long term due to silicosis.
GREENSTRIPE FIRECLAY:   An air floated and flash dried Lincoln Fireclay.  It is a secondary clay, high in Aluminum Oxide and refractory with a melting point of 2970° F. Fires a buff color in oxidation and a brown color in reduction.  Fireclay deposits were formed over 200 million years ago and most are found under coal seams.  Due to the nature of their formation they all contain high amounts of volatiles (materials that burn out during firing) and slow firing is recommended if large amounts are used in clay bodies.  Some grogs are made of fired and crushed fireclays. Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
GROG:  A granular additive typically composed of fired clays and/or bricks that are ground and screened to specific sizes.  Used in clay bodies for the addition of texture, to control drying and firing shrinkage and to impart greater strength to unfired clay.  Acute effect:  Mild irritant.  Chronic effect:  Mild irritant.
GROLLEG KAOLIN:   A blended English primary kaolin of moderate plasticity, low shrinkage, high melting point (2012° F) and a very low iron content lending to its snowy white color.  An excellent kaolin for making translucent porcelain bodies due to its low titania content.  With a flux content higher than other kaolin, less feldspar is needed to achieve vitrification.  Its plasticity can be an issue for thrown bodies, as the addition of most plasticizers may impact the clean whiteness of the clay. Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
GUM CMC: (Carboxymethylcellulose)  This organic compound is used as a glue, glaze binder and suspending agent.  Up to 3% may be used and it is helpful to first dissolve the gum powder in warm water, then add the gum solution to the glaze or slurry.  Dust may become flammable.  Acute effect:  Mild irritant.  Chronic effect:  None reported
HAWTHORN BOND:   A Missouri fire clay that fires a light buff color at cone 10.  This fireclay like all fireclays is a refractory and it has good plasticity. Very similar to AP Green fireclay in its properties but at a lower cost. Fireclay deposits were formed over 200 million years ago and most are found under coal seams.  Due to the nature of their formation they all contain high amounts of volatiles (materials that burn out during firing) and slow firing is recommended if large amounts are used in clay bodies.  Some grogs are made of fired and crushed fireclays.  Acute effect:  Mild irritant.chronic effect:  May be hazardous over long term due to silicosis.
ILMENITE: (FeTiO3)  An iron titanate that is closely related to rutile.  In fact, Titanium containing under 15% iron is called rutile and if it has more than 15% it is called ilmenite.  It is a granular material used to create speckles in glazes and clay bodies and up to 1% is used as ‘seeds’ in crystalline glazes.  Acute effect: Non-hazardous.  Chronic effect:  Non- hazardous.
IRON CHROMATE: (FeCrO3)  A blend of iron and chromium oxide used in underglazes, engobes, clay bodies and glazes to yield grays and blacks.  Colors will vary depending on other chemicals present.  Can also give opacity to glazes.  Acute effect: Mild irritant.  Chronic effect:  May be hazardous over long term.
IRON OXIDES:  General group name for compounds of iron and oxygen.  Third most common element on earth, after aluminum and silicon and is the main contaminant in most clay materials.  Yields many different colorations including reds, browns, yellows, blacks, and grays depending on usage and firing atmosphere.  It should be noted that iron can be a very powerful flux in reduction.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
IRON OXIDE, RED: (FeO)  Called ferric oxide or hematite, it is the most stable form of iron producing yellows, oranges, reds and browns.  Its fine particled nature allows it to spread evenly in slips and glazes but also allows it to be spread by finger prints to unwanted surfaces.  Used by jewelers as a polishing abrasive called rouge.
​*Available in natural (#521) and synthetic (#4686) varieties. The synthetic produces a brighter red.
IRON OXIDE, BLACK: (FeO)  Called ferrous oxide or magnetite, it is the simplest of  the iron oxides.  Produces blacks and greens in glazes and contains slightly more iron than red iron oxide.
IRON OXIDE, YELLOW: (Fe2O3·H2O)  Hydrated iron oxide disperses well in solutions. It is used extensively in paints and enamels and is one of the main   components of yellow ochre clay.
KENTUCKY STONE CLAY:   A coarse grained ball clay mined in the Kentucky-Tennessee Valley area with good plasticity, high strength and firing temperature into the cone 10 + range. Generally stone clays are ball clays that contain more sand and color impurities.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
KT 1-4 BALL CLAY:   Mined in the Kentucky Tennessee Valley this coarse grained cone 10 ball clay is a blend of K-T clays SGP#1 and OM#4 clays.  Since KT1-4 is blended it allows for a more exact and stable product that is adjusted to compensate for mineral shifts in the two base clays.  While not the most plastic of ball clays it is one of the preferred ball clays for making casting slips.  Kentucky Tennessee ball clays are low in carbon which helps prevent the formation of gas bubbles in glaze mixtures that are stored for lengths of time. The term ‘ball’ clay comes from the old hand mining technique where small blocks were cut from deposits, the corners of which would get knocked off during handling and storage, leaving roundish balls of clay.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
LITHIUM CARBONATE: (Li2CO3)  A source of lithium oxide, it is used to lower coefficients of expansion and contraction in glazes, as an additional fluxing agent and as a stoneware flux.  It can change color responses and create special effects such as halos, breaking glazes, and salt glazes effects.  Acute effect:  Mild irritant.  Chronic effect:  None Reported.
MAGNESIUM CARBONATE: (MgCO3)  A source of magnesium oxide for glazes and clay bodies that disperses readily in mixtures.  It is an opacifier that helps produce matte glaze surfaces in temperatures below 2100°F.  At temperature ranges above 2100°F it becomes an active flux. Magnesium carbonate may not be the best choice of catalyst in clay bodies as it can change the clays workability. Talc should be substituted as a magnesium oxide source.  Acute effect:  Mild irritant.  Chronic effect:  None reported.
MAGNESIUM SULPHATE: (MgSO4)  A colorless transparent crystal commonly know as Epsom salts.  Used as a flocculant (thickener) in glazes to help them adhere to over fired bisque or non-porous (glazed) surfaces.  A few teaspoons dissolved in warm water are added slowly to the glaze mix until the desired thickness is reached. (around 0.1% to 0.5%)  Caution should be used as large amounts in clay bodies can cause salt scumming.  Acute effect:  Mild irritant, seek medical advice if large quantities are ingested.  Chronic effect:  None reported.
MANGANESE CARBONATE: (MnCO3) A weak coloring carbonate used as a source of manganese oxide.  In leaded glazes it can produce purples and in alkaline glazes it can produce blue/purple colors.  The carbonate disperses better in glaze mixtures than the oxide, giving more even color tones.  Acute effect:  Poisoning can occur from excessive inhalation and extremely large ingestion.  Chronic effect:  Hazardous over long term, may affect central nervous, blood and respiratory systems.
MANGANESE DIOXIDE: (MnO2)  A metal oxide that produces blacks, browns and violets.  In terra-cotta bodies, around 5 % can be added to produce dark grey to black colors.  In glazes, large amounts (over 20%) can produce metallic surfaces, which are NOT dinnerware safe.  The fern like stains in Mocha ware are achieved with the combination of tobacco juice and manganese dioxide.  It does release oxygen at temperatures under 2000°F, which may cause pin holing in glazes.  Above 2000°F it becomes a flux which reacts with silica to produce violet colors, or, if alumina is present, browns that have a softer more pleasant tone than those produced by irons.  Acute effect:  Poisoning can occur from excessive inhalation and extremely large ingestion.  Chronic effect:  Hazardous over long term, may affect central nervous, blood and respiratory systems.
MULLITE: (2Al2O3 · 2SiO2)  An important ceramic silicate crystal that forms in high temperature (over 2100°F) clay bodies during the firing process.  Although rarely found in nature, it is named after a deposit found on the Isle of Mull in Scotland.  Mullite crystals are long needle like structures that interlace as they grow lending to a strong clay body.  Acute effect:  Mild irritant.  Chronic effect: May be hazardous over long term due to silicosis.
NEPHELINE SYENITE: (K2O · 3Na2O · 4Al2O­3 · 9SiO2)  A member of the feldspathoid family (minerals having properties similar to true feldspar), nepheline is used as a flux in clay bodies used to make tiles, sanitary ware, porcelain and many different grades of vitreous clay bodies.  It can yield a porcelain body as low as cone 4 to 6 and can be a substitute for normal feldspars in clay or glazes mixtures due to its low melting point.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term.
NEWMAN RED CLAY:   A high fire California clay that is low in plasticity with powerful staining properties.  The raw clay is orange in color but fires a bright rich red, used to color plastic clays and casting bodies.  Its coloring abilities are so strong that recipe amounts can many times be cut in half and still produce rich reds in oxidation clay bodies. Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
NICKEL OXIDE: (Ni2O3)  A general name for nickel and oxygen compounds used as powerful colorants in glazes.  Nickel can produce greens, grays, blues, and pinks that vary depending on the recipe and firing conditions.  As little as .02% will produce slight tints in glazes with 3% being the typical upper limit.  Nickel oxide is available in both green and black forms but both are typically 99% nickel and will produce the same glaze results.  Acute effect:  Strong irritant.  Chronic effect:  Considered carcinogenic and can cause pulmonary disorders.
OM# 4 BALL CLAY:   A strong, fine grained, highly plastic ball clay named for its source, Old Mine # 4 located in Kentucky.  OM#4 is an industry standard widely used as a suspension agent in glazes, excellent for casting slip suspensions and provides superior plasticity in thrown clay bodies.  Its melting point is 3000°F and it does contain some soluble salts.  The term ‘ball’ clay comes from the old hand mining technique where small blocks were cut from deposits, the corners of which would get knocked off during handling and storage, leaving roundish balls of clay. Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
OCHRE: (Yellow)  Ochre, also called gall clay, is a fine clay mineral containing high concentrations of iron oxides.  If the term ochre is used alone then it is assumed Yellow ochre is called for in the mixture.  Other forms of ochre, such as Black (“shadow”) Ochre and Red (“ruddle”) Ochre, are typically named specifically in recipes.  All ochers will turn to the normal red/brown tones in oxidation firings; however, yellow ochre can be kept a yellow color through the use of specific fluxes and oxides.  Commonly used as a colorant in engobes, washes, underglazes and glazes.  Acute effect:  Mild irritant.  Chronic effect:  Mild irritant
PUMICE: (Volcanic Rock)  Also called pumice stone, it is volcanic glass that is extremely porous due to gas bubbles trapped as lava cooled.  Easily crushed, it is used as a cleaning abrasive or as a high silica feldspar frit.  Volcanic ash, known as pumicite, is a finer grained variety of pumice that is emitted in clouds during eruption.  Pumice and pumicite from different volcanoes have different chemical properties.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term.
PYROFRAC 2024:  A commercially produced mineral product derived from pyrophyllite ores.  Used in making refractory clay bodies, industrial ceramic products, as a shrinkage reducer and to widen firing ranges.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term.
RED ART CLAY:   A 200 mesh air floated iron red clay with moderate plasticity, low shrinkage and a firing range of cone 04-1.  Colors will vary with firing conditions and temperatures with the richest color achieved at cone 02. This type of red earthenware clay has been used to make flower pots for many years and is often called flowerpot red. Gardeners will use iron red clays for the making of seed balls.  Acute effect:  Mild irritant. Chronic effect:  May be hazardous over long term due to silicosis.
RUTILE: (TiO2)  The mineral name for natural titanium oxide containing up to 15% contaminates of iron, chromium, tin and other minerals. (more than 15% contamination and it is called ilmenite)  Often called a colorant, rutile is more a catalyst for other colorants creating mottling, streaking, speckling, breaking effects, mattes, crystalline and phototrophic (reversible and continuous color shifts caused by light levels) effects.  The varied and inconsistent nature of its composition makes rutile a fun spontaneous glaze material but be warned; glaze results will tend to change in character over periods of time.  Acute effect:  Mild irritant.  Chronic effect:  Mild irritant.
SILICA: (SiO2)  A material with many names and many functions.  Silicon dioxide is the name of its pure chemical form.  Quartz is a natural mineral composed mainly of silicon dioxide, flint is a high quartz content stone with limestone contaminations and silicates are silicon dioxide chemically combined with other oxides forming minerals with crystalline structures.
            Silica is the most abundant mineral on the planet making up to 60% of the Earths crust.  It is a hard glassy material with a melting point of over 3100°F.  When blended with aluminum oxide and water, basic idealized clay is formed.  When raw silica is added to clay bodies it introduces extra or ‘free’ silica that is not bound to the clay particles giving the body its strength.
            In glazes a finer grain (325 mesh) is used to encourage a better melt, where as clay bodies use a courser grain (200 mesh).  The basic differences between silica, silicates and silica sands are the amounts of silicon dioxide they contain, the types of contaminants found in them and how they are bonded together.  These differences give us a phenomenally wide range of materials to use in ceramics.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
SILICON CARBIDE: (SiC)  A synthetic compound created through the combination of silicon and carbon by baking sand and coke.  Nearly as hard as diamond, it is used as an abrasive and in the manufacturing of high heat kiln shelves.  It can also be used to make crater and foaming glazes and is useful in creating reduction effects in oxidation firings.  Acute effect:  Mild irritant.  Chronic effect:  May be Hazardous over long term due to silicosis.
SODA ASH: (Na2CO3) Sodium carbonate is used in combination with sodium silicate as a deflocculant in ceramic slips and alone as a preferred deflocculant for thinning glazes.  Not normally used as a source of sodium oxide in glazes as it is very soluble.  Acute effect:  Mild irritant.  Chronic effect:  None reported
SODIUM SILICATE: (Na2SiO3)  Also called water glass, it is used as a glue, an egg preservative, a hardener, a binder, a fireproofer.  In ceramics it is one of the most popular deflocculants and almost always used in combination with soda ash.  Once sodium silicate dries, if forms a glassy crystalline surface that is very brittle and VERY SHARP.  Acute effect:   Moderate irritant.  Chronic effect: None reported
SPECTRALUX 3500: (ZrSiO4)  A glaze opacifier used as a cheaper alternative to tin oxide.  It is the brand name of this commercially manufactured zirconium silicate.  Used in amounts of up to 15% to increase a glaze's opacity and whiteness.  Can be used at all temperatures.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
SPODUMENE: (Lithium Feldspar)  This feldspathoid mineral is a good source of natural lithium oxide (a powerful flux) for glazes and clay bodies.  In glazes it can lower the fusion range, increase glossy surfaces and improve stability.  In clay bodies, it can be used to develop flame ware bodies and aid in the formation of mullite crystals.  Acute effect:  Mild irritant.  Chronic effect:  may be Hazardous over long term.
STRONTIUM CARBONATE: (SrCO3)   Used as a source of strontium oxide in glazes since the carbonate form is less soluble than the oxide.  Often used as a barium substitute in the production of matte glazes, but care should be used as it can be a cause of pin holing and blistering in glazes.  Acute effect: Nuisance dust.  Chronic effect:  None reported.
SUPERPAX: (ZrSiO4)  A glaze opacifier used as a cheaper alternative to tin oxide.  It is the brand name of this commercially manufactured zirconium silicate.  Used in amounts of up to 15% to increase a glaze's opacity and whiteness.  Can be used at all temperatures.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
TALC: (3MgO · 4SiO2 · H2O)  Magnesium silicate, soap stone.  It is a source of the flux magnesium oxide in glazes and clay bodies, is less likely to cause glaze bubbles (pin holing), can promote matte surfaces and opacity in low fire glazes and in stoneware bodies it is used to increase resistance to thermal shock.  Used in slip casting bodies in proportions up to 50% and up to 60% in low fire bodies to increase thermal expansion and help them fit commercial glazes better.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
TIN OXIDE: (SnO2)  A pure, high grade white powder used in proportions of up to 15% in glazes to impart opacity and whiteness.  Used as an opacifier for over 600 years with the most famous examples being Maiolica from Italy and Delftware from England.  Tin oxide is more expensive than zirconium opacifiers but it does generally yield a richer more creamy opaque white.  Acute effect:  Non-toxic, Mild irritant.  Chronic effect:  Dust may cause stannosis over long term exposure.
TITANIUM DIOXIDE: (TiO2)  Used to create crystals in glaze melts producing varied effects.  Amount of 5 to 10% yield a crystalline opacity with soft matte surfaces.  When added in small amounts (up to 5%) to opaque colored recipes the crystal formation can produce attractive color shifts and variegations.  Acute effect:  Nuisance dust.  Chronic effect:  May cause light lung fibrosis.
UMBER (BURNT):  One of the oldest coloring pigments know to man, raw umber is a brown clay mineral containing iron and manganese oxides.  When calcined (heated) the coloration intensifies, thus the name burnt umber.  Named for a region in central Italy called Umbria, but found in deposits all over the earth.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.
WOLLASTONITE: (CaSiO3)  Calcium silicate used as a source of calcium oxide and silica in glazes and as a strong flux in clay bodies at temperatures over 2000°F.  It is especially useful in viscous glazes that are susceptible to crawling such as celadons.  Acute effect:  None reported.  Chronic effect:  Mild irritant.
ZINC OXIDE: (ZnO)  When used in glazes in small amounts it is a flux, a hardener and an anti-scaring stabilizer.  In larger amounts it can promote soft mattes and crystalline effects.  In simple glazes, zinc may heighten coppers and cobalts, yet in more complex glazes it may interfere with color development.  Can also cause crawling due to high shrinkage rates in its raw state.  Acute effect:  Inhalation may cause metal fume fever, mild skin irritant.  Chronic effect:  Irritant.
ZIRCOPAX: A glaze opacifier used as a cheaper alternative to tin oxide.  It is the brand name of this commercially manufactured zirconium silicate.  Used in amounts of up to 15% to increase a glaze's opacity and whiteness.  Can be used at all temperatures.  Acute effect:  Mild irritant.  Chronic effect:  May be hazardous over long term due to silicosis.