It is known as "Thematic Development".
Craftsmanship, design, aesthetic properties, & how well the work reflects the society it was created in
Because they have a creative mind
Some of these vessels have a cup-shaped cover over the mouth, so that they seemed to be used to store high quality wine such as insamju (인삼주, ginseng wine) or maehwaju (매화주; rice wine made with plum)[6] It would have originally had a lid and there are many maebyong with ginseng leaves on the surfaces.[7]
