A magnesia speckle matte at cone 6 oxidation is impossible, right? Wrong!

I am getting closer to reduction speckle in oxidation. I make my own speckle by mixing the body and a glossy glaze 50:50 and adding 10% black stain. Then I slurry it, dry it, fire it in a crucible I make from alumina, crush it by hand and screen it. I am using G2934 cone 6 magnesia matte as the glaze on this mug on the left. To it I added 0.5% minus 20 mesh speck. Right is a cone 10R dolomite matte mug. Next I am going to screen out the smallest specks, switch to a matte glaze when making the specks (they are too shiny here), switch to dark brown stain. Later we will see if the specks need to bleed a little more. I am now pretty well certain I am going to be able to duplicate very well the reduction look in my oxidation kiln. I will publish the exactly recipe and technique as soon as I have it.

Related Pictures

Making your own crucibles to make your own speckle

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I mixed a cone 6 porcelain body and a cone 6 clear glaze 50:50 and added 10% Mason 6666 black stain. The material was plastic enough to slurry, dewater and wedge like a clay, dry and break into small pieces. I then melted them at cone 6 in a Zircopax crucible (I make these by mixing alumina or zircopax with 3-4% veegum and throwing them on the wheel). This material does not completely melt so it is easy to break the crucible away (it does not stick to the zircon). I then break the black up with a special flat metal crusher we made, size them on sieves and add them to glazes for artificial speckle. If specks fuse too much I can lower percentage of glaze (and vice versa). Of course, the particles are glass, jagged and sharp-edged so care is needed in handling them.

Reduction speckle: a product of iron particles in the body

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In reduction firing, where insufficient oxygen is present to oxidize the iron, natural iron pyrite particles in the clay convert to their metallic form and melt. The nature of the decorative speckled effect depends on the size of the particles, the distribution of sizes, their abundance, the color of the clay and the degree to which they melt. The characteristics of the glaze on the ware (e.g. degree of matteness, color, thickness of application, the way it interacts with the iron) also have a big effect on the appearance.

Oxidation fired speckled glaze!

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The magnesia and calcia matte base glazes we have developed for electric firings have soft surfaces that rival the feel and utility of those achievable in reduction-fired dolomite mattes. By adding 0.2% granular manganese to M340 clay we can achieve this speckled aesthetic (outside of mug) using G2934 matte glaze.

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Glossary	Dolomite Matte Dolomite matte glazes have the potential to be very silky and pleasant to the touch, while at the same time being hard, durable and non-crazed (if they are formulated correctly).
Glossary	Reduction Speckle A sought-after visual effect that occurs in reduction fired stoneware. Particles of iron pyrite that occur naturally in the clay melt and blossom up through the glaze

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