They appear as tiny grains of sand like material on the glass surface or small rocks imbedded in the glass. They are not only unattractive but may interfere with your cutting wheel. Always inspect the edge of a piece of glass. Look for irregular thick or thin edges that are not a part of the normal texture of the glass. Look at the edge of the glass where two colors meet.
Bad mixes look as if one color is trying to flake away from the other color.
If the glass has a very irregular, uneven edge as shown above, it is probably because it is difficult to cut and has broken in an unnatural way. Another clue is the unsuccessful score mark vertically in the picture. Pay attention to the cut. Look for scores on the surface. Appearance problems are different and some what subjective, since one person may not like a particular affect, while the next person can't live without it.