What is the use of brush washing in calligraphy?

Pen washing, also called ink washing, is a kind of stationery that was put on the desk in ancient times and filled with water to wash the writing brush. Because the writing brush is extremely delicate, if it is not cleaned immediately after use, the glue in the ink will corrode the nib, so washing the pen is often a necessary thing in the study. Generally, the shape of the washing pen is shallow, which requires the pen mouth to be smooth and not hurt the writing brush. The shape and specifications of the body are different, such as round, sunflower, sugarcane segment, peach, lotus leaf and lotus flower. Materials include copper, jade and porcelain. The former is mostly carved, while the latter has various glaze colors, paintings and sculptures.