At a master craftsman’s studio, there are usually several artisans that specialize certain aspects of the production process. Rosanjin Kitaoji’s studio was no exception. Rosanjin had a love for the dark red glaze and worked tirelessly to find the perfect mixture of Gosu that would result in the desired specific color when taken out of the kiln. At his studio, one individual focused his expertise into mixing and making the perfect red glaze, thereby becoming the master of Aka-gosu; his name was Koetsu Yamakoshi. This set of tea cups were made by Yamakoshi himself. Aka (red) Gosu Glaze is applied on the outer surface and at the bottom of each cup, “Kotobuki” (longevity) is written with the Indigo Gosu Glaze. Works like these showcase the immense abilities that artisans such as Yamakoshi had acquired; artisans that dedicated themselves to perfecting a certain aspect of the studio’s works and are undeniably masters themselves. They are the possessors of great knowledge, capable of creating impeccable works.