Silicon carbide powder produces gases at the top end of a stoneware firing and will create glaze bubbles. You can find lots of examples by googling the term and clicking the "images" link. Many of these will have accompanying information (especially about how to fire the kiln). Be alert to the possibility that it might be more practical to put the SiC powder into a glaze you already use (using the amount of firing method explained on the resource you find).
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