Glaze color is a combination of chemistry between the colorant and host, firing process and the amount and nature of the colorant. It is possible to achieve very similar colors using very different systems, and very different colors by making very small changes in a system. Often the trade offs associated with different approaches to making a similar color can be quite complex.
- The opacity of the ground of this glaze depends very heavily on the composition of the clay body upon which the glaze is used. The ground is transparent on most porcelains; on some stonewares such as B-Mix and and Loafer's Glory, the ground is opaque and the color generally darker.
Oxides - MnO2Manganese and cobalt mixture produce black. Iron can also be used. For example, a mix of 8 iron, 4 manganese dioxide and 0.5 cobalt make a raw black stain.- Chrome is a constituent in almost all black oxidation colors. It is used up to 40% in Cr-Co-Fe blacks and as high as 65% in Cu-Cr blacks.
Oxides - FeOClassic reduction black-breaking-to-brown tenmoku glazes are made with 8-12% iron.- CoFe, CoCrFe stains are suitable for most types of transparent glazes. The tendency of cobalt-based colors to soften the fired glaze can be overcome by the addition of china clay or silica to the batch before the stain is introduced.
Underglaze Color: Suitable for most types of glazes to 1300C+. In this application the best results are obtained with colors having a low cobalt content, minimizing the risks of cobalt diffusing into and tinting the glaze blue.
Oxides - CoOCobalt is a classic and reliable blue colorant at all temperatures and in most types of glazes. The shade of blue can, however, be affected in many ways by the presence of different oxides. Cobalt is powerful and often less than 1% will give strong color. If the color needs to be toned down, additions of iron, titanium, rutile and nickel may work.Oxides - Li2OLithia can produce blue effects with copper.Oxides - K2O0.5-1.0% iron in potassium reduction glazes may give delicate blue to blue green.Oxides - CuOCopper in a barium/zinc/sodium glaze gives a blue. Color can also be enhanced by
lithia.
Tin and copper can produce turquoise to robin's egg blue.- In reduction glazes Fe2O3 tends to fire bluish or turquoise to apple green with high soda (boric oxide may enhance). 0.5% iron with K2O may give delicate blue to blue green.
Oxides - FeOThe presence of phosphorous pentoxide, lithia and soda also encourage blue in both normal and saturation conditions in reduction firing.
Iron glazes will move toward blue if alumina is low.Oxides - NiONickel with zinc oxide can produce steel blues. With larger amounts of zinc, lavender blue can be made.- 5-8% added rutile can give powder to deep blue colors in reduction. These colors can be brilliant and mottled with shades of browns and tans. Rutile effects can be hard to Like copper reds, rutile blue reduction effects depend on adequate silica being available (7 times or more that of alumina).
Classic rutile blue glazes are best made by using rutile in fluid glossy bases. The amount of iron in the rutile (or from the body) determines the degree of blue since its reduction to FeO is a key to the effect. Since rutile is variable in makeup, changes in the iron content will change the blue color. The fact that titanium dioxide additions do not make good blues suggests that the iron-titanium mix is the key to good color.
Silky matte variegated blue glazes can also be made with rutile additions.
If you employ this type of glaze be sure that you have a large supply of rutile on hand and test new supplies throughly.
Oxides - B2O3Low fire transparent glazes employing boron frits, which have CaO and lack alumina, will have opalescent blue cloudy effects from the formation of calcium borate crystals. These 'boron blue' glazes work well visually on terra cotta bodies. These crystals do not form well if there is adequate alumina to stiffen the melt.
Oxides - CoOCombinations with iron and manganese can give a slate blue.
Oxides - CoOCobalt is often calcined with alumina and lime for soft underglaze colors. Stains often employ mixes of alumina, cobalt, and zinc for softer blue colors.
Oxides - CoOWith chrome and manganese blue-black and black are common.
Oxides - Cu2OFluoride, when used with copper, can produce blue green colors.Oxides - CoOWith barium shades of blue-green are possible.Oxides - CoOWith chrome and copper, cobalt can yield tints from pure cobalt blue, to greenish-blue, to the green of chromium. These effects work best when silica is not too high and there is adequate alumina.
- In an alkaline glaze, manganese carbonate can produce blue-purple and plum colors.
- CrSi stains are suitable for all types of leadless glazes to 1450C. Chrome greens should be used for staining only zinc-free glazes. Chrome-cobalt blue-greens may be used for staining both zinc-free and zinc-containing glazes, the better results generally being obtained with the zinc-free glazes.
Additions of stain should not normally exceed 4%. Zircon may be used as an opacifier; tin oxide should never be used.
Underglaze Color: Suitable for all methods of underglaze decoration in all firing conditions.
- Lead cadmium frits are available as a base to create classic cadmium selenium colors that cannot be easily achieved in other ways. These glazes can be toxic to work with and the glazed ware will likely leach cadmium.
- Lead cadmium frits are available as a base to create classic cadmium selenium colors that cannot be easily achieved in other ways. These glazes can be toxic to work with and the glazed ware will likely leach cadmium.
- Lead cadmium frits are available as a base to create classic cadmium selenium colors that cannot be easily achieved in other ways. These glazes can be toxic to work with and the glazed ware will likely leach cadmium.
Oxides - MnOVery pleasing tan-brown reduction fired glazes can be achieved with 5% manganese dioxide in reduction.- Chrome in zinc glazes tends to form the stable crystalline compound, zinc chromate (ZnCr2O4)
- Iron produces a wide range of browns in bodies and glazes at all temperatures.
Oxides - FeOSaturated reduction iron glazes normally firing to black in reduction will move toward brown if alumina is high, toward blue if alumina is low.Oxides - MnOIn glazes below 1080C, manganese can give coffee color browns when used with tin and dull browns in lead and low alkaline glazes. The presence of alumina assures brown (if it is lacking colors will be violet).Oxides - NiONickel with barium can produce brown. In high sodium glazes it can fire brown also.- Rutile produces many shades from pale straw to tan to cinammon brown to orange brown. Alkaline glazes experience less of the classic rutile crystalline effect. Color intensifies with increased amounts and tends to be darker in reduction.
Oxides - FeOWhen 1-5% iron is used in a transparent reduction glaze which has some calcia and potash (barium also helps) celadon glazes are produced. 'Celadon' glazes are glossy shades of green which exhibit depth of color due to suspended micro-bubbles in the glass.
Oxides - K2OCobalt blues can be very intense in alkali glazes (up to 2% cobalt).
- Cobalt depends on the presence of alumina or it will fire pinkish. Chrome reds like alumina also.
Oxides - Na2OOxidation copper blues work best in high alkaline, low alumina glazes. Increasing copper to 4-6% will move color toward turquoise.Oxides - K2OOxidation copper blues work best in high alkaline, low alumina glazes. Increasing copper to 4-6% will move color toward turquoise.
Oxides - K2OCopper red reduction glazes are best in formulations with high alkali. The presence of boron can give a more pleasant red.Oxides - Na2OCopper red reduction glazes are best in formulations with high alkali. The presence of boron can give a more pleasant red.
- Frits with very high alkali and little or no alumina can develop these colors well. However they have very high thermal expansion so it is difficult to get them to fit most bodies.
- Glaze must
be zincless & have a whiting content of 12-15% (CaO 6.7-8.4%).
Oxides - ZrOZirconia is used in stains to stabilize colors.
Oxides - CaOCalcia likes to form yellow crystalline compounds with Fe2O3 producing a 'lime matte', especially in fluid glazes. Thus iron glossy brown or black glazes should be low in CaO.
- The golden color of the rutile crystals shades all colorants added to this glaze toward the yellow. In light reduction, all crystals become decidedly golden and ground (in the absence of other colorants) becomes a pale mauve.
- Chrome is a classic green colorant for recipes in oxidation and reduction at all temperatures. However, the shades it produces can be opaque, dull, and uninteresting. In the presence of CaO, the color moves toward grass green.
Oxides - CuOUnder normal oxidizing conditions CuO produces clear green colors in most glazes. The shade of green depends not only on the amount but also on other oxides present (i.e. lead in larger amounts will enhance and darken the green, the presence of alkalies or high boron will shift it toward blue).
Copper in calcium/magnesium glazes gives a green very different from that produced with lead.Oxides - NiOIn the presence of high MgO, nickel can produce greens. Zinc is also helpful to develop color.- Rutile and cobalt can crystallize to form green glazes.
- Drab chrome greens can be moved toward peacock green with the addition of cobalt oxide (1% each gives bright color, some MgO needed also). This works in zinc free boron and soda glazes.
Oxides - CuOK2O can turn a copper glaze yellowish. If Na2O or PbO are present, K2O should not exceed 0.15 equivalent.
- Suitable for all types of glazes for firing at temperatures up to over 1300C (1250C for Zr-Pr-V).
Zircon is recommended as an opacifier, although tin oxide may also be used.
Underglaze Color: Suitable for all methods of underglaze decoration.
Unlike victoria greens, vanadium greens are suitable for use under all types of glazes.
Oxides - NiONickel in lead glazes tends to produce grey colors.
Oxides - CoOWith adequate SiO2 and high MgO (0.4 molar), purple, violet, lavender, and pinks can be made using 1% or more CoO. Mimimizing boron, alumina, and KNaO will help prevent it from turning blue. Note that the high MgO will generally make the glaze matte and it could suffer some ill effects associated with excessive MgO.
- Frits with very high alkali and little or no alumina can develop these colors well. However they have very high thermal expansion so it is difficult to get them to fit most bodies.
Oxides - Cu2OLarge amounts of copper in a glaze give metallic and even graphite effects.- Large amounts of manganese can produce metallic effects in a glaze. However, these glazes must not be used on food surfaces.
Oxides - CuO7% copper in glossy oxidation glazes can produce striking metallic green colors.
- Ground is completely opaque except where glaze pools or when applied very thickly to tiles. Crystals are tinted toward the golden and are sometimes quite yellow. Copper gives olive green and nickel is simply not a match, but cobalt, iron, manganese and most stains will color this glaze very well. Crystals are large and profuse. Matures at cone 9.
- Crystals will be more yellowish than the ground, which is generally a soft white when no colorants are used. Cobalt used in this glaze yields blue crystals on a mustard-colored ground; copper crystals and ground shaded toward light grass green.
- Chrome in high lead glazes forms yellow lead chromate. Zinc and chrome tend to produce orange.
- Suitable for all types of glazes, although best results are obtained with leadless glazes having low alkali and boron contents. Used extensively for producing shades of ivory at low percentage concentrations.
Overmilling the colour when adding to glaze should be avoided as it tends to weaken the colour rapidly. Advisable only to slop the stain as it disperses readily.
Underglaze Color: Excellent stability, especially in decoration of porcelain at high temperature in reducing atmosphere.
- In zinc glazes powdered rutile develops an orange-tan color.
- When Celestite crystalline glaze is used immediately, crystals are often a pale aquamarine even when no actual colorant is added. Copper in small amounts is influenced toward turquoise or cyan.
Oxides - K2OAlkaline glazes with barium and small amounts of Mn can produce pink.- Alumina is used in combination with chrome, manganese, and cobalt to achieve pink colors.
Oxides - Li2OLithia can produce pinks and warm blues with cobalt.Oxides - NiONickel can produce pinks in high potash or lead glazes.- Glaze must be /n/nzincless & have a whiting content of 12-15% (CaO 6.7-8.4%).
Oxides - SnO2Chrome and tin are the most well known way to produce pink. For example, 7.5% tin and 0.5 chrome oxide will produce pink. Many Cr-Sn stains are available to make many shades on pink. However this mechanism requires that the glaze chemistry be right (e.g. no zinc, boron not excessive) for slow firings (in industry firing is typically so fast that the stain does not get an opportunity to react with the zinc).
- Chrome and tin are a widely used combination to produce pinks in zinc free glazes with at least 10% CaO and low MgO (alkaline glazes work well). Many stains are based on this system and typically have around 20-30 times as much tin oxide as chrome oxide. Tin would typically be around 4-5%.
- Chrome-tin pinks move toward purple in glazes with significant boron. One glaze with 3.3 SiO2, 0.27 Al2O3, 0.2 B2O3, 0.15 Li2O, 0.5 CaO, 0.1 MgO, 0.15 Na2O employed 5% tin oxide, 0.6% cobalt carbonate, 0.17% chrome oxide to produce a good purple at cone 6.
Oxides - CoOWhen cobalt occurs with manganese (i.e. 1-3% cobalt carb, 3-5% manganese carb), purples and violets can be made. Less cobalt will lighten the color. This effect works well in magnesia glazes. In high magnesia glazes, 1-2% cobalt alone will give purple. Add tin to move the color toward lavender.Oxides - Cu2OThe use of boron in a copper red reduction glaze will give a purple hue.
The following formula produces good purple at cone 10: BaO 0.1, CaO 0.5, MgO 0.1, KNaO 0.2, ZnO 0.1, B2O3 0.15, Al2O3 0.2, SiO2 3.0.- In leaded glazes manganese carbonate can produce purple tinged with brown.
Oxides - MnO2Purple colors can be produced in glazes of high alkali (KNaO) and low alumina, especially in combinations with cobalt (look for a frit with this profile for best results).
Oxides - SeUsed in making red glazes with cadmium for low fire. Lead enhances the coloration.Oxides - CdORed enamels are made using cadmium-selenium-sulfur mixes because this combination goes into solution readily during the short firing period (copper compounds are too slow to dissolve). Great care is required to maintain the correct slightly reducing atmosphere during firing. Cadmium zirconium encapsulated stains are also an option where cadmium by itself is not practical or workable.Oxides - TiO2In high fire matte glazes, iron oxide and titanium can produce red colors.Oxides - U3O8It is possible to achieve reds in lead silicate glazes low in alumina and having no boric oxide. Zinc is also helpful to develop the color.Oxides - CoOWith MgO, SiO2, and B2O3, red, voilet, lavender, and pinks can be made.Oxides - Cu2OCopper is well-known for its ability to produce blood-red and fire-red colors in steady reduction atmosphere firings where CuO is altered to Cu2O. See example copper red recipes in RECIPE area.
Bright red colors are usually achieved with very small amounts of copper (i.e. 0.2-0.5%) in a low alumina base with at least .4 molar equivalents of CaO and plenty of the alkalis. Tin oxide will enhance color. Use of silicon carbide in oxidation (2%) can produce red.- Small silicon carbide additions to copper glazes fired in an oxidation kiln will produce reduction effects.
- Below 950C in high lead, low alumina glazes, chrome will produce reds to ranges, often with a crystalline surface. The addition of soda will move the color toward yellow.
Oxides - ZnOZinc reacts with chromium to form the very stable crystalline compound zinc chromate (ZnCr2O4).
- Low fire lead, potash and soda glazes encourage reddish colors with iron. Should be barium free.
Oxides - FeOA typical high-temperature fluid reduction glaze with 15% iron will freeze to a sparkling rust colored mesh of crystals. Alkaline glazes work best. Barium can impede this effect.
- Areas not crystallized are opaque where the glaze is thin. Opacity is somewhat streaky. This glaze does not show as much opacity as a glaze containing titanium dioxide would and is a good choice if titanium is to be avoided.
Oxides - NiONickel with calcium can produce tan.
- Rutile can produce soft tan colors due to its iron content, especially in matte glazes.
Oxides - K2OReduction tenmoku black-rust glazes with 8-10% iron work well in high potash glazes.
Oxides - BaOBarium glazes are well known for thier ability to produce matte turquoise colors with copper. While strontium is often used to duplicate the matte texture of barium it does not have the same color response.Oxides - Cu2OIn copper red glazes, barium additions in a high feldspar base will produce turquoise to deep blue depending on how much copper is added. Lithium contributes to the color also.
Oxides - CuOCombinations of CuO with tin or zircon will give turquoise or blue-greens when the glaze is alkaline (KNaO) and low alumina. Look for a frit with this profile for best results. Glazes of this type often craze.
- When used with up to 2% copper carbonate, magnificent true turquoises and cyans result (due to interaction with tin and calcium).
Oxides - K2OAlkaline dominant glazes will produce violet, purple, burgundy, red blue using manganese dioxide to 2%.
Oxides - U3O8Yellow is the usual oxidation color for uranium modified glazes. The presence of CaO and ZnO are beneficial.Oxides - CdOCadmium is blended with uranium to produce yellow optical glass and yellow enamels. For example, a yellow stain for enamels can be made with 12% selenium, 64.5% cadmium sulfide, and 23.5% cadmium oxide.Oxides - NiOIn lithium glazes nickel can produce yellow.Oxides - V2O5A classic yellow colorant.Oxides - CaOIn oxidation, iron glazes calcia likes to form yellow crystalline compounds with the Fe2O3 producing a 'lime matte' even in an otherwise fluid glaze.Oxides - CeO2In combination with titanium, cerium produces a yellow glass.- It can give a yellowish color if the glaze contains lead, this is a result of the precipitation of yellow lead antimonate (known as Naples yellow).
Oxides - CoOCobalt is used in combination with manganese and selenium to mask excess yellow coloration (yellow plus blue gives green which is masked by the pink of selenium).- Chrome in high lead glazes forms yellow lead chromate. Alkalies are recommended in the base glaze. Added zinc can extend the range to orange.
In other types of glazes, less than 0.5% chrome oxide will give yellowish or yellow green tints.
- Fe2O3 tends to fire yellowish with calcia and in alkaline glazes straw yellow to yellow brown.
In reduction, 3-4% iron with 0.4 BaO, 0.15 KNaO, 0.25 CaO, 0.2 MgO, 0.3 Al2O3, 1.7 SiO2 and 15-20% zircon opacifier will produce a yellow opaque.
- Although the colours are primarily intended for use as body stains, their low cost compared with that of other types of orange stain favours their use as glaze stains for firing at temperatures below 1100C.
A fairly stiff leadless glaze mixture should be used, and the addition of stain should not exceed 5%.
Underglaze Color: Suitable for use under most types of glazes.
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