Final answer:
Round brushes used in Chinese calligraphy can have a core made of various materials, including bamboo, wood, and porcelain. The bristles of the brush are typically made from selected animal hair. However, metal is not used as a core material for round brushes.
Step-by-step explanation:
Round brushes used in Chinese calligraphy can have a core made of various materials, including bamboo, wood, and porcelain. The bristles of the brush are typically made from selected animal hair.
However, based on the given information, the core material that is NOT used for round brushes in Chinese calligraphy is metal.
So, the answer to the question is that a round brush may have a core made of any of the following materials: bamboo, wood, or porcelain, but not metal.