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.
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 (and no zircon sticks). 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.
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