Had this same problem…

[katkramer]

I used to have this problem…I was cutting my Bullseye cabs on a tile saw, and firing on thinfire.  I frequently got the cloudy edges.

I found that if I use a “glass brush” or even a toothbrush and dishwashing detergent to clean the cabs before firing, then fire directly on kiln wash, I get perfect results.  The glass brush is used by enamel artists when they grind down cloisonne enamels, and it gets the tiny particles of glass out of the ground edges.