ARMADILLO CLAY & SUPPLIES

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

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.

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 sever 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.

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.

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.

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.

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.

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.

   RED IRON OXIDE (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.

   BLACK IRON OXIDE (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.

   YELLOW IRON OXIDE (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.

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.

MAGNESIUN 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.

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.

OCHRE (Yellow):  Ochre, also called gall clay, is a fine clay mineral containing high concentrations of iron oxides.  If the term ocher is used alone then it is assumed Yellow ocher is called for in the mixture.  Other forms of ocher, 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.

PETALITE (Li₂O · Al₂O₃ · 8SiO₃):  Petalite (lithium feldspar) is a feldspathoid used in the production of flame ware and other low expansion bodies.  Lithium is a strong alkaline flux and can create unique color reactions with coppers and cobalts.  Flame ware bodies containing up to 50 – 60% petalite have extreme resistance to thermal shock, but it is almost impossible to make glazes that will fit them.  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.

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.

SPODUMEME (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.

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.