The grooves are only a few millimeters deep and must be carefully engraved by hand by the artisans. Additionally, the grooves become deeper as it gets closer toward the center of the mill, virtually invisible to the naked eye. The artisans are a dying breed and only AIYA houses veteran artisans who train young artisans to continue the 120 year tradition. Only seasoned artisans know the feel for the stones and are skilled enough to maintain such delicate balance and perfect calculation. This tradition of artisans is as old as AIYA itself and will continue to be passed on to future generations.
Please watch Aiya's artisan's interview.