The appearance of devitrification varies from mild streaks as a dirty appearance on the surface, to at worst a granular surface that breaks away in small pieces. The glass will often have raised sharp corners in cases of severe devitrification.
Avoiding devitrification relates to cleaning, firing rapidly through the devitrification range, avoiding devitrification-prone glasses, and grinding edges as little as possible.
Repairing devitrification requires the removal of the devitrified surface. This can be done by sandblasting, sanding the surface by hand, using acid pastes to remove the surface. Then the piece needs to be fired again to a fire polish.
To ensure a polished surface a devitrification solution may need to be applied. It can be a commercial product or a borax solution. Any devitrification solution should be applied evenly.