All Glossary

Cone 6

Also called "middle temperature" by potters, cone 6 (~2200F/1200C) refers to the temperature at which most hobby and pottery stonewares and porcelains are fired.

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Details

This refers to the medium temperature oxidation range (or middle fire) that most potters work in using electric kilns. Orton cone 6 fires to about 2200F (or 1200C). Potters who fire ware cone 5 or 7 may also consider themselves to be working at "cone 6" (using the term to designate the range or type of ware). This range represents the best investigated and experimented glazes among potters and hobbyists, there are millions of images on line of ware being made and commercial products that support it.

Cone 6 is the lowest practical range for feldspar-fluxed white plastic bodies. Vitreous porcelains can be made with up to 30% feldspar (the remainder being silica, 20-25% is needed to prevent crazing, and kaolin/ball clay). White stonewares need about 20-25% feldspar. Typically a bentonite addition is needed to augment plasticity. Buff and brown burning bodies offer more flexibility since they often employ clays that already contain natural quartz and fluxing minerals (so less feldspar powder is needed).

Clays made using feldspar can be made to vitrify to zero-porosity density at cone 6 (including porcelains and stonewares). Since vitreous ware can be made at cone 6, many do not bother with the extra time, trouble and expense of firing to higher temperatures. Companies making prepared glazes serve the middle temperature range with a wide array of products.

Related Information

Mason stains in the G2934 matte base glaze at cone 6

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Stains can work surprisingly well in matte base glazes like the DIY G2934 recipe. The glass is less transparent and so varying thicknesses do not produce as much variation in tint as glossy bases do. Notice how low many of the stain percentages are here, yet most of the colors are bright. We tested 6600, 6350, 6300, 6021 and 6404 overnight in lemon juice, they all passed leach-free. The 6385 is an error, it should be purple (that being said, do not use it, it is ugly in this base). And chrome-tin pink and maroon stains do not develop the color (e.g. 6006). But our G1214Z1 CaO-matte comes to the rescue, it both works better with some stains and has a more crystal matte surface. The degree-of-matteness of both can be tuned by cooling speed and blending in some G2926B glossy base. And it’s easy to turn any of these into brushing or dipping glazes.

Mason stains in the G2926B base glaze at cone 6

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This glaze, G2926B, is our main glossy base recipe. Stains are a much better choice for coloring it than raw metal oxides. Other than the great colors they produce here, there are a number of things worth noticing. Stains are potent; the percentages needed are normally much less than for metal oxides. Staining a transparent glaze produces a transparent color, it is more intense where the laydown is thicker - this is often desirable in highlighting contours and designs. For pastel shades, add an opacifier (e.g. 5-10% Zircopax, more stain might be needed to maintain the color intensity). The chrome-tin maroon 6006 does not develop well in this base (alternatives are G2916F or G1214M). The 6020 manganese alumina pink is also not developing here (it is a body stain). Caution is required with inclusion stains (like #6021). Bubbling, as is happening here, is common - this can be mitigated by adding 1-2% Zircopax. And it’s easy to turn any of these into brushing or dipping glazes.

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