The Tetsu-kuro (Iron-black) chawan (matcha bowl) is made from red clay glazed in an iron-black liquified clay similar to the time-honored kohiki (white slip) method. The kohiki style is revered in Japanese tea culture for its historic value and humble aesthetic. Sugawara Kengo's iron-black chawan reveals rustic variations and a stunning iridescence, putting a spin on traditional pottery. The base is finished with a takenofushi koudai (bamboo-node foot ring), and the rim is shaped with a mutual spout, making it ideal for whisking and pouring matcha.

Kengo-san founded Yōki Kiln near Mount Katsuragi where the Shugendo fire ritual began, which is yet believed to transform the world's corruption into goodness. He applies the Shugendo ritual to his own ritual of transforming the earth's clay into a peaceful tea experience using his wood-fired kiln.

Handmade Japanese tea wares are referred to as Kogei in Japan; the concept that beauty resides in the artisan’s work through nuances, wabi-sabi (irregularities), and defining differences between each piece.