I too just took out some student work and had 1 piece have the edges look cloudy I am not sure why as all the other pieces have turned out perfect, in the same batch. I have to say it must have been the glass, or the student grinding the glass before firing. What other explanation could it be?
Hopefully we will be able to lap it and it will come off and she can polish it.
I also think sometimes you can have an area in your kiln that might just be hotter, thus the devit.
Good Luck in your search for glassy looking pieces.
Just a thought. You said you are using Moretti? If that is true you will run into problems with that sheet glass. It is not as well made as BE, SPEC, and the other fuseable glasses. It does cloud up