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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.
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.
I control the recipe and temperature I use to make it and now I need to control the particle size. I have already smashed it up (using a special flat hammer we have) and am now sizing it. That involves getting what I can through the screen and then going at the larger sized particles with a hammer again. I use three screen sizes in the procedure so that I can control the distribution of sizes in the fired product (to more closely match reduction fired ware). This can be a dusty procedure and those particles are angular and sharp and high in heavy metal, so it would be better to do this outside in a breeze or with a ventilator and mask inside.
Glossary |
Crucible
In ceramics, potters make crucibles to melt frits, stains and other materials. Crucibles are made from refractory materials that are stable against the material being melted in them. |
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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 |
Materials |
Calcined Alumina
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