Hi! I’m so glad that I’m not the only one experiencing the dark stoneware problem and thank you for all the helpful advices! Currently I’m using black mountain and throughout the years I have very unstable results with this clay, bloating, glaze crawling or blistering (I’m using a simple white tin glaze that sometimes works fine but most of the time isn’t) and it is very frustrating. I tried not stacking them giving them space during bisque, tried firing it at 900 and 1000c and problem still occurs! Haven’t tried holding the temp during bisque yet as I’m firing it at a communal space but hopefully someone here can solve the the mysteries!
Mariane