I am also a novice at fusing
I am also a novice at fusing glass. But I also wonder if it is do to the glass being “clean”. I found out early on both glue type and how clean, or not clean, the glass is can contribute to disappointing firings, like white film.
What I have found helpful is to make a record of what I used to design a piece. I have a notebook, I log the sizes, type of glass, glue used etc. I record all this BEFORE ITS FIRED. After firing, I add comments as to the firing temps/times and the result, and then try and decide what I could have done differently if I have a poor result, or with a great result what to do to achieve the same result in a future piece.