Cavity bubbles.jpg

My understanding is bubbles quite often are not buoyant enough to rise through the viscous glaze. To some extent a successful glaze is constrained by the need to not run under the influence of gravity. Is it unreasonable to say glazes with no interior bubbles are likely rare and then  by that reasoning at what point should become  concerned?

Blisters  indicate pressure, especially if they have raised rims.  The holes are only 1/32 or so, but 200x makes them look huge. However, it is enough to cause weeping. Bubbles are normal for off gassing spars and can be remedied. Blisters, even if a few typically indicate the body has been compromised. Bubbles can come from a glaze, and sometimes blisters: but blisters more often come from the clay; sulfides and spars. 

Understood but the text box in the picture seams to imply the surface could heal but the bubbles on the inside are?  Maybe ok, maybe not - or is this over thinking?

You have it. Once pores open up within the body: game over. I have looked at many stoneware samples under the scope; seen few that did not have some level of imperfections.

Can you post a picture of the same body that's been fired properly?