Opaque white and specks

[Gail L]

I used BE opaque white in a pattern bar. The glass was cleaned prior to firing. There was no dirt anywhere.
The slab came out of the kiln... there were black specks on and "in" the opaque white. (not many...but they are there)
I cut the bar and discovered black specks contained "in" the opaque white. I will call BE tomorrow but was wondering if anyone
else has had something similar happen to them.
It wasn't until I actually cut "into" the white glass were they obvious.

Could it be some kind of debris that was on the glass either on the top or bottom of the white. Could a piece of debris
migrate "into" the white while it was firing ? It didn't cause any bubbles.