Mottled or spotted referred to colors which were somehow damaged and stained, it was a defect. But since the mid-nineteenth century, ceramics started to be produced, characterized by a mottled brown glaze. Later it was improved by a technique of applying a glaze, sprinkle with spots of oxides to give a mottled effect in blue, brown, black, etc. Today commercial glazes are sold prepared with this effect.
Photos by Jordi Marcet and Rosa Vila-Abadal