Glossary of Glaze Colorants

Please be kind and cite me too!   Short Link for this Page: http://wp.me/PxVXW-3F


NB: Some entries may be repeated in other parts of the Glaze Resource.


abbreviations you may see on these pages:

CoTE – coefficient of thermal expansion

(http://en.wikipedia.org/wiki/Coefficient_of_expansion)

SG – specific gravity

(http://en.wikipedia.org/wiki/Specific_gravity)

MSH – Mohs scale of hardness

(http://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness)


References used in the entire Glaze Resource

  • my personal experience gathered through glaze testing
  • http://ceramicartsdaily.org/daily/glossary/ – Used as a starting point, to remember all the terms I should include and all but copy definitions that were so well written I could not have improved upon them.
  • http://www.galleries.com/ – pictures and information on minerals and rocks
  • http://digitalfire.com/4sight/oxide/index.html – Digitalfire is awesome.  We use their glaze calculation software which I highly recommend you purchase and use.  It will help you fix all kinds of problems and keep your glazes within alumina and silica limits.
  • Ceramics and Glaze Technology.  J.R. Taylor and A. C. Bull.  Pergamon Press, New York.  1986.  ISBN 0 08 033465 2
  • Electric Kiln Pottery: The Complete Guide. Emmanuel Cooper.  BT Batsford, London. 1991.  ISBN 0 7134 4037 6
  • Clay and Glazes for the Potter. Daniel Rhodes.  Chilton Book Company, Radnor, PA.  1973.  ISBN 0 8019 5633 1
  • The Complete Guide to High-Fire Glazes: Glazing and Firing at Cone 10.  John Britt.  Lark Books, Sterling Publishing Co, Inc, New York.  2004.  ISBN 1 57990 425 4
  • Simon and Schuster’s Guide to Rocks and Minerals. Annibale Mottana, Rodolfo Crespi, and Giuseppe Liborio.  Martin Prinz, George Harlow, and Joseph Peters Editors.  A Fireside Book, New York.  1977.  ISBN 0 671 24417 5
  • A Potter’s Book.  Bernard Leach.  Faber and Faber, London.  1976.  ISBN 0 571 10973
  • Glazes for the Craft Potter.  Harry Fraser.  Adam & Charles Black, London.  1973.  ISBN 0 7136 2481 7
  • The Potter’s Complete Book of Clay and Glazes. James Chappell.  Watson-Guptill Publications, New York.  1991.  ISBN 0 8230 4203 0

bone ash

raw material (flux and color modifier)

sources/names: calcium phosphate [Ca3(PO4)2]

  • high temperature flux (calcium) and glass former (phosphorous)
  • can cause blue-ish flush from suspended phosphorus globules as in Chun glazes
  • advantageous to making rich iron reds
    • If the ratio of iron to bone ash is out of balance, the iron red will tend to mottle with either brown, black or green depending on the constituents of the base glaze.  The base glaze shown in the pictures below was feldspathic and high in magnesium.

[picture of A to R line line blend with iron and bone ash]

  • toxic in inhalation
  • Chun
    • pale, blue-grey feldspathic stoneware glaze the color of which is due to  phosphorous inclusions
    • –> (NOTE: April 28, 2010) Robert was reading Nigel Wood’s book to me while I was driving back from a show recently, and I have to amend this definition.  The Chun blue effect is indeed due to spherules of immiscible glass floating in the larger glass matrix.  These are of the appropriate size to scatter blue light and not other wavelengths thus making the glaze appear blue to your eye.  The effect is not strictly dependent upon phosphorous, and instead is much more constrained by silica and alumina limits (isn’t everything).  However, researchers have determined that the effect can be enhanced by the addition of phosphorous to glazes which are withing the appropriate silica-alumina limits.  The effect is also very dependent on firing cycle, particularly during the cooling phase.
  • http://en.wikipedia.org/wiki/Bone_ash
  • refer to phosphate for more information

breaking

glaze term

  • when a glaze has a different color where it is thin as on rims and ridges where it has run away from these areas
  • e.g. Em’s Tenmoku Black breaks to rust on rims.

Em's Tenmoku Black

Tenmoku glazes should exhibit marked breaking over rims and edges.

ceramic pigment / stain

  • calcined (melted, fused) mixtures that have been ground to a powder to ensure a particular color response

cerium

raw material (glaze colorant)

sources/names: cerium oxide [CeO2]

melting point: 2400oC (oxide)

Cerium Oxide Testpots

Cerium Oxide needs to be mixed with other oxide to develop a yellow color.

chrome

raw material (glaze colorant)

sources/names: green chrome III oxide [Cr2O3], potassium bichromate (toxic – K2Cr2O7), lead chromate (toxic)

melting point: variable: 2257 – 2427oC (chrome III oxide) volatilizes at: 1241oC / 2265oF

  • mostly green – true red (only with lead, typically toxic), pink, brown, yellow, apple to avocado green colorant

[picture of chrome green tests]

  • refractory and tends to opacify glazes
    • chrome oxide is only soluble in glazes high in alkali (particularly lithium) or boron
  • very strong coloring power, only 1-2% needed
  • as little as 0.25% can modify other colors
  • combined with tin produces pink
    • In my experience, the best “chrome-tin pinks” use tin in 10-20 times excess of chrome.
    • In a clear base glaze, Cr-Sn pink can tend more toward red.  An opacifier corrects this.
    • Calcium and magnesium are good fluxes for Cr-Sn pinks.

Chrome Tin Pink

Various Chrome Tin Pink Glazes with and without Opacifiers

  • combined with zinc (>4%) produces brown
  • combined with cobalt produces blue-green
  • combined with manganese produces muddy colors
  • brown in reduction
  • boron improves the quality of green produced by chrome
  • barium and sodium base glazes encourage yellow-green (<1%)
  • vaporizes above 1200oC and may effect other pieces in the kiln; “flashing”
    • This is a problem if you are using tin as an opacifier in what is meant to be a white glaze on an adjacent pot.  It can cause a quite attractive pink flush on tin glazed pieces but is almost impossible to control and reliably reproduce.  Good Luck!
  • Highly toxic (inhalation/fumes and ingestion)
  • http://www.galleries.com/minerals/elements/chromium/chromium.htm
  • http://digitalfire.com/4sight/oxide/cr2o3.html

cobalt

raw material (glaze colorant)

sources/names: cobalt oxide [Co3O4], cobalt carbonate [CoCO3]

melting point: 1805oC / 3281oF (oxide)

  • strongest coloring oxide: 0.25% will generate a noticeable blue in a transparent base glaze

[picture of sky blue]

  • soluble in glaze melt (will bleed if used as underpainting)
  • strong flux
  • magnesium glazes alter blue to pink or purple speckling on a blue background

[picture of cobalt pink tests]

  • on its own, creates a harsh blue that benefits from iron, manganese, rutile, ilmenite, nickel, copper, and chrome
  • high alumina bases tend toward green with cobalt
  • essential for deep black colors
  • atmosphere and firing temperature do not change the color
  • when chloride ions are present, it will volatilize and flash onto nearby pots
  • cobalt oxide / Co3O4 (mix of CoO and Co2O3)
    • calcined cobalt carbonate
    • about 1.4X stronger than carbonate
    • coarser particle size than carbonate which may cause mottling in glaze
    • 71-72% cobalt atoms
  • cobalt carbonate / CoCO3
    • finer particle size giving more uniform color in glaze
    • 47% cobalt atoms
  • cobalt sulfate / CoSO4.7H2O
    • can be used as an underglaze painting
  • smalt and zaffre / cobalt aluminate or silicate stains
  • Toxic (inhalation and ingestion)
  • http://www.galleries.com/minerals/elements/cobalt/cobalt.htm
  • http://digitalfire.com/4sight/oxide/coo.html

copper

raw material (glaze colorant)

sources/names: copper carbonate (CuCO3), copper oxide black (CuO), copper sulfate

melting point: (CuO) 1478oC / 2098oF / (CuCO3) 500oC / 932oF

  • 1 – 3% (oxide, up to 5% carbonate) generates a range of greens from mint to forest
  • In an alkaline, low alumina base glazes can make “Egyptian” blue which is a dark turquoise blue.
    • In my experience, these are often outside the limits for “stable” glazes and they tend to craze as they need to be very low in alumina.

[picture of low alumina line blend]

  • very soluble in glaze melt, producing uniform colors
  • strong flux
  • >5% copper carbonate (3-4% copper oxide) will likely result in devitrification of the copper and its crystalline deposition onto the surface of the glaze (attractive but definitely not food safe).

copper crystals in glaze 1

Too much copper will crystalize on the glaze surface and will act as a flux.

copper crystals in glaze 2

Too much copper will crystalize on the glaze surface.

copper crystals in glaze 3

Too much copper will crystalize on the glaze surface.

  • Copper increases the solubility of lead and should not be used to color glazes fluxed with lead.
  • Boron containing base glazes may generate turquoise hues.
  • Barium blues result from copper, but are often matte and not suitable for food.
  • Calcium and magnesium may encourage pink from copper (<1%) if also soaked at high temperature.
  • Copper produces a wonderful red in reduction in feldspathic, alkaline base glazes (oxblood, sang de boeuf), tin and iron accentuate this red.
  • At higher temperatures (1050oC / 1922oF), can volatilize and flush adjacent pieces in the kiln.
  • Copper has a high COE which contributes to crazing.
  • copper carbonate [CuCO3]
    • green in oxidation, red in reduction
    • less powerful colorant than copper oxide black
    • toxic
  • copper oxide black, cupric oxide [CuO]
    • same color response as copper carbonate, but more powerful
    • coarse particle size
    • toxic
  • copper sulfate [CuSO4]
    • used in saggar and pit-firing
    • soluble
    • highly toxic (absorption, ingestion, and inhalation)
  • http://www.galleries.com/minerals/elements/copper/copper.htm

erbium

raw material (glaze colorant)

sources/names: erbium oxide

melting point: 2400oC (oxide)

Erbium Oxide Testpots

Erbium Oxide generates a lovely baby pink at many different concentrations.

frit

A mixture of raw materials that have been melted/fused into a glass and crushed/ground back to a powder, in order to give greater chemical stability and to eliminate toxicity resulting from water solubility of raw material.

ilmenite

raw material (glaze colorant)

sources/names: erbium oxide

melting point: 1800oC (titanium dioxide)

iron

raw material (glaze colorant)

sources/names: iron/ferric chloride, iron chromate, black iron oxide (ferrous), red iron oxide (ferric), synthetic iron oxide [Fe3O4], yellow iron oxide / ochre, crocus martis [FeSO4], ilmenite, rutile, some native clays (e.g. Georgia red)

melting point: 1350oC (Fe2O3) / 1565oC / 2849oF (decomposition of Fe2O3)

  • Iron oxides from different manufacturers or produced at different times can vary widely in composition and should be batch tested for consistency with your previous formula.
    • Synthetic iron oxide will have the most consistent composition.
  • For an in depth look at ancient Chinese and Japanese iron glazes, please see my article in this blog http://wp.me/pxVXW-29.  This article covers Kaki Persimmon, Tessha, Tenmoku, Tea Dust, and Ohata Red glazes.
  • Iron is soluble in the glaze melt and contributes to fluxing at high temperatures when converted to FeO.
  • In feldspathic, alkaline base glazes under oxidizing conditions iron produces tan, cream, yellow, olive green, black, red, and brown.
  • In reduction, very small amounts of iron will produce green and blue (celadon).
  • Iron and zinc can be muddy or tend to green depending on the base glaze.

[picture of mossy mahogany]

  • Titanium tends to make iron more orange.
  • >8% iron generally generates the same colors in oxidation or reduction.
  • Dissolved iron can devitrify during cooling generating crystals on the glaze’s surface when used at high percentages.
  • iron chloride [FeCl2·6H2O]
    • soluble metallic salt
    • fuming agent
    • Highly toxic (inhalation and ingestion)
  • iron chromate [Fe2O3·Cr2O3]
    • pink or red with tin, brown with zinc, gray in alkaline base glazes
    • Highly toxic (absorption, inhalation, and ingestion)
  • black iron oxide (ferrous) [FeO]
    • reduced iron oxide
    • stronger than red iron oxide
  • red iron oxide [Fe2O3]
    • essentially, rust
    • refractory until cone 7-8
    • converts to FeO (flux) in reduction and/or at high temperatures
  • yellow iron oxide / ochre [Fe2O3]
  • http://www.galleries.com/minerals/elements/iron/iron.htm

kaki

see http://wp.me/pxVXW-29

line blend / triaxial blend / quad blend

process

  • different approaches for systematically testing the effect a glaze material has on the final, fired glaze
  • the different methods vary the proportion of one or more materials through serial dilution

manganese

glaze colorant

sources/names: black manganese dioxide [MnO2], brown manganese carbonate [MnCO3], Barnard clay

melting point: 535oC / 995oF (dioxide)

  • weak colorant
  • acts as a flux
  • alkaline base = purple and red
    • a nice lilac can be made in a feldspathic, alkaline, low alumina base glaze, but it will tend to craze

[picture of manganese lilac]

  • soft yellow-brown (typical of most base glazes)

[picture of manganese brown]

  • In my experience, carbonate works better than dioxide as it disperses better in the glaze melt and gives more uniform color.  Dioxide is fine if working toward black.  As always, the problem with carbonates is the evolution of gas from the melt which may cause bubbles and pinholes if the glaze does not have sufficient “open time”.
  • with cobalt and iron produces a very deep black
  • small amounts of cobalt carbonate (0.5 – 1%) with manganese (3 – 4%) produce lovely blue plum colors

[picture of blue plum]

neodymium

raw material (glaze colorant)

names/sources: neodymium oxide (Nd2O3)

melting point: 2320oC

  • produces a very pretty pale lilac in most base glazes

[picture of neo test pots]

nickel

raw material (glaze colorant)

names/sources: green nickel carbonate [Ni2CO3], black nickel oxide [Ni2O3], green nickel oxide [NiO]

melting point: 1990oC / 3614oF

  • excellent modifier of other oxides
    • grey-blue with cobalt
    • darker iron reds
  • refractory, use less than 2% for most glazes, otherwise it will impact the viscosity of the melt
  • volatilizes at high temperatures, generating toxic fumes
  • alone: grey, green, brown
  • yellow with titanium (~ 10 Ti : 1 Ni), tends to crystallize

[picture of crystalline yellow]

  • steel blue with zinc

[picture of ni blue]

  • pink with barium (strontium substitution does not seem to work as well)
  • green nickel carbonate [Ni2CO3]
    • weaker
    • reduces to green nickel oxide during firing
    • Toxic (ingestion and inhalation)
  • black nickel oxide [Ni2O3]
    • reduces to green nickel oxide during firing
    • Toxic (ingestion and inhalation)
  • green nickel oxide [NiO]
    • Toxic (ingestion and inhalation)
  • http://www.galleries.com/minerals/elements/nickel/nickel.htm

nuka

glaze type

  • silica white
  • typical Japanese glaze
  • contains significant amounts of rice-hull ash

[nuka test pot and as underglaze]

opacifier

  • any compound that does not melt in the glaze causing diffraction of light which is perceived as opacity

phosphorous

raw material (glazes)

names/sources: bone ash, DCP/TCP calcium phosphate, wood ash, plant ash, amblygonite, frits

melting point: 44.1oC (element), 280oC (elemental boiling point)

  • glass former
  • creates colloidial opacity (suspended phosphorus in glaze melt) and a blue-ish flush
  • high COE, contributing to crazing
  • see bone ash

praseodymium

raw material (glaze colorant)

sources/names: praseodymium oxide [PrO2]

melting point: 931oC (element)

  • lanthanide series, rare earth element
  • weak colorant
  • In my experience, praseodymium produces a chartreuse yellow-green in a feldspathic, calcium fluxed base glaze.

Praseodymium Testpots

Praseodymium oxide generates various shades of chartreuse.

rutile

raw material (glaze colorant and additive)

sources/names: rutile light, medium, dark, granular and ceramic

melting point: 1825oC / 3317oF

  • TiO2 ­ore with contaminating iron up to 15%
    • light, medium, and dark grades are dependent on the amount of iron
  • usually tan or peach when used alone at >5%

[picture of peach tests]

tenmoku

tessha

tin

raw material (glazes)

sources/names: tin chloride, tin dioxide

melting point: 1127oC (oxide)

  • Tin II Chloride / SnCl2 / stannous chloride
    • soluble, metallic salt
    • creates mother-of-pearl luster on glazed surfaces
    • Highly toxic (inhalation and ingestion)
  • tin IV oxide / SnO2 / stannic oxide / white tin oxide
    • most powerful opacifier, insoluble in glaze melt
    • 5–7% will produce opaque, high gloss white
      • zircon and tin together opacify better than better than tin alone
    • essential to majolica
    • color stabilizer
      • except with chrome and vanadium
    • Toxic (inhalation and ingestion)
  • http://www.galleries.com/minerals/elements/tin/tin.htm

titanium

raw material (glazes)

sources/names: titanium dioxide, rutile, sphene

melting point: 1870oC / 3398oF (oxide)

  • matting agent, promotes crystal growth (nucleating agent)
  • opacifer
  • increases variegation and visual texture

Titanium Dioxide Underglaze

Titanium dioxide underglaze generates lots of surface interest.

transition metals

  • coloring oxides
  • color is due to their interaction with neighboring ions as well as to the valence of the metal
  • Cr, Co, Fe, Mn, Ni, Cu, Va, Ti

zirconium

raw material (glazes)

sources/names: zirconium oxide, zirconium silicate, “Zircopax”, igneous rocks, granite

melting point: dissociates above 1540oC

  • opacifier
  • 10-12% in a clear glaze should create white
  • not as strong an opacifier as tin oxide
  • refractory, especially in silicate form
  • low COE (especially silicate) and may increase craze resistance
  • increases mechanical strength and chemical resistance of final glaze
  • http://www.galleries.com/minerals/silicate/zircon/zircon.htm
  • zirconium oxide / ZrO / zircon
  • zirconium silicate / ZrSiO4 / “Zircopax”
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10 thoughts on “Glossary of Glaze Colorants”

  1. iffet orbay said:

    Is there a way to see your line blend test > «picture of A to R line line blend with iron and bone ash», that appears in your «Bone ash» information? I’m interested in the BoneAsh – RIO balance you point out…

    Thanks in advance,
    iffet

    • Hi There! Sorry that’s one of those pictures I haven’t taken yet. I’ll dig those out of the test tile box and take that picture sooner rather than later. Depending on the effect you are looking for, excess or equivalent bone ash to rio ratios work for different things. I’ll get on it as soon as I’m back from vacation! 🙂 Thanks for looking and asking!
      Emily

  2. Looks great. Thanks for sharing. When are you posting more pictures?

  3. how to galze pottery now live in my blog

  4. Very worthwhile illustrated glossary, the photos and personal comments makes a huge positive difference to other such lists.

    I’m just curious as to when the rest of the photos will be added. 🙂

  5. pls give me information how to prepare coral-pink,

  6. Omkar P Nagarkar said:

    Hi!
    I wish to prepare orange colored refractory oxide.
    Which raw material shall I take?
    Also I have a furnace,temp of which goes upto 700°C,
    Which material shall I use to reduce the temperature of the final oxide?
    Regards
    Om

  7. Did you leave out Barium for a reason?
    Thanks,
    Lisa

    • Hi Lisa,

      While Barium is an important secondary flux, and certainly alters the shades different colorants produce (especially copper), it’s not actually a colorant itself. For the most part I think people use it because calcium often reduces the vibrancy of certain colourants, and Barium restores this.

      I personally also don’t use it as it’s somewhat toxic. When I’m testing recipes that call for Barium Carbonate, I substitute in Strontium Carbonate instead. There’s already so much testing to do it’s not something I’ve looked at in depth!

      Robert

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