Blistering, pinholing; whatever you want to call it different words for the same annoying problem which turns perfectly good firsts into seconds instantly. Glaze blistering is an issue with glazes which use more volatile metallic compounds in their formation. Unfortunately there’s no guaranteed way of getting rid of these.
I’ve recently been experimenting with the way the kilns fire to minimise this problem, extending the time for both the glaze and biscuit to get the gasses from both released at about 700 degrees. All this information about kiln firing cycles can probably be found in your instruction manual – if your like me it’s likely that you read through this just the once while programming your kiln.
Another thing I’ve been using is both the vents and the bungs which came with the kiln, again these are advised to be used in the manual. This helps to provide a smooth operation at the higher 800 degree temperatures by creating a sealed chamber for the hot air to circulate better.
The biggest difference is that I’ve also introduced a cooldown cycle as I found the drop off from the top temperature to be too fast, as the kiln cools down these glazes are still active so it’s important not to skip this. You can find a great article about kiln cooldown over on Ceramic Arts Daily.
Even with all these changes I’ve still found a few glazes which have a more reactive nature to continue to blister so your mileage may vary with these tips.