vbean

Hoping someone can help me...I am having using ceramic decals on porcelain cups which are glazed on the inside but not on the outside. I am getting random black marks which vary in size and appear to be in the body of the cup, not able to me sanded away. These vary from cup to cup and sometimes don't appear at all. I am posting from Australia so I hope my specs make sense. I am firing the porcelain to 1280 and the decals to 820 degrees Celsius. And have followed all the instructions from...