yohen 窯変
窯 kiln · 変 change
Yohen refers to changes in a ceramic's color and shape that occur unexpectedly inside the kiln, from flame, ash, and the placement of the piece during firing. The effect is produced by the firing itself rather than by painting; with advances in technique it can now also be sought intentionally.
During firing, yohen effects emerge as areas of darker transformation shaped by kiln atmosphere and placement. On tenmoku glazes, iron oxide crystals rise to the surface, creating iridescent halos and patterns that shift with the light.