First, cook the board to make it soft and tough, then slowly press it with a curved mold to bend it, then let it dry naturally in the shade for seven days, and then take it off the mold. This method should not be too curved and the board should not be too thick. To make a ball shape, the diameter of the ball needs to be larger, I estimate it is more than 20 cm. According to the above method, make four petals from thin wooden boards and then splice them together.