You can make your own crucibles from materials that have a high melting point (like alumina, zircon or even fireclay). If the material is non-plastic it can be plasticized by the addition of bentonite or veegum. Crucibles should be prefired to a higher temperature than what they will be used at. If the crucible is made from a material having a poor resistance to thermal shock (e.g. alumina), care is needed not to subject it to sudden temperature changes (it could crack in a spectacular fashion and cause real issues if the material inside is still molten). Certain melts can be highly corrosive and may be able to dissolve their way through crucible walls, so be sure to do tests on smaller melts before attempting a bigger one. Cordierite, for example, has very good thermal shock properties, but may not be as resistant to attack by the melt.
Making your own crucibles
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, so I dried a slab and broke it up into small pieces. I then melted them at cone 6 in a zircopax crucible (I make these by mixing alumina or zircopax with veegum and throwing them on the wheel). Because this black material does not completely melt it is easy to break the crucible away from it. As you can see no zircon sticks to the black. I then break this up with a special flat metal crusher we made, size them on sieves and add them to glazes for artificial speckle. As it turned out, this mix produced specks that fused too much, so a lower percentage of glaze is needed. I can thus fine tune the recipe and particle size to theoretically duplicate the appearance of reduction speckle.
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