I single fire and spray multiple glazes. In recent months, I started having more and more pinholes and blisters on the glaze surface when single firing in an electric kiln. At first, I thought it was my glazes and particularly an interaction between two glazes. But noooooooooo.
After some research, I realized that I was not providing enough oxidation during the early firing cycle. Highwater Clay ( Asheville, NC ) has a great tech tip page : http://www.highwaterclays.com/files/Preventing%20Pinholes,%20Blisters,%20Craters,%20and%20Bubbles.pdf
My envirovent motor had quit working, and I was using a floor fan and ceiling fan when firing, but not leaving all the peeps open until "glowing red". Now that the kiln is getting enough oxygen, and allowing proper burnoff, the pinholes and blisters are gone....my glazes are just fine.
Note: I use Steven Hill's firing cycle and downfire to 1600 degrees before shutoff. A recent article by Tony Hansen ( Digital Fire) suggests firing to temperature and holding for 15 minutes, then, cooling down 100 degrees and soaking for 45 minutes. ( might try this ).