This firing error subjects the material to excessive heat work, causing clay bodies to bloat, warp, or melt completely. In glazes, it can lead to running off the pot, blistering, or burning out volatile colorants. The damage is usually irreversible, turning carefully constructed wares into fused puddles on the kiln shelf.
Heard on the job
If you overfire that earthenware clay to cone 6, it will turn into a puddle on the shelf.