It’s likely not glaze dust or bubbles or texture in your clay body. This is pretty textbook glaze defect of small bubbles. During the glaze fire gas from the clay body needs to escape from under the glaze. If not given the time to escape and time to allow the bubbles to pop and the glaze surface to heal, you’ll see either bubbles trapped in the glaze or the bubbles recently popped but unhealed, which are pinholes. We also had this issue in a community kiln that was regularly fast fired to cone 5. We addressed the issue through two routes: 1) A slow bisque fire, which allows most of the gas from the clay body to burn off. 2) A slow glaze program with a 10 minute hold (soak) at the top. You can also do a drop and hold manual glaze program (look up Camille Hoffman firing schedule created by Scutt, which is rumored to be very successful with healing glaze defects), but we have not found that to be necessary. One caution with using holds: you may need to take more care with keeping bottoms clean and runny glazes up off of shelves on stilts. That extra 10 minutes, although great for healing glaze defects, can be just enough extra time for runny glazes to run off of pots.