There is a color Korean potters spent roughly two hundred years learning to fire: bisaek, the jade-grey-green of sky after rain. Chinese connoisseurs of the 12th century - not a crowd given to flattery - ranked Goryeo celadon "first under heaven." The secret was a glaze chemistry and reduction firing so finicky that whole kiln loads were smashed for falling short of the color.
The Korean innovation that China never matched was sanggam: carving designs into the clay and inlaying them with white and black slip before glazing - cranes and clouds floating inside the glaze rather than painted on top of it. Look at a celadon teapot's cranes and you are looking through the surface, not at it.
The lineage never broke. Today houses like Kwangjuyo - heir to the royal kiln tradition that supplied the Joseon court - fire celadon and white porcelain for daily use: teapots, cups, plates built on five centuries of court standards but priced for a dinner table.
Our celadon and royal-lineage porcelain lives in Hidden Korea, with tea ware gathered in The Ritual. For the three-object way into Korean tea itself, see our dado starter guide.