You probably raked some of the reaction layer (the dark line between the steel blue and antique white) into your clear.
I've made beads with that combo (and I think they're better than moretti Ivory/Aqua
), but I haven't encased or spot encased them.
How long did you heat the clear before you raked it? If you heat long enough/too close to the torch face, you can burn your clear. ( I'm not going to admit to HOW I know that, or anything, though.....)