The “white splotches” are likely devitrification, which can be caused by a number of issues, including improper cleaning. There are devit sprays (store-bought or home-made) that can be used and the piece can be refired. Or, you can sprinkle a fine layer of clear powder over the piece and refire.
“Google” fused glass devitrification and you will find a lot of information.
Jester’s Baubles Fused Glass Designs