Many times the pieces to be curved should not be placed face down in a metal or wood well and be dapped because their surfaces could be damaged. Also, one cannot see what is happening to the surface of a piece during the forming process.
Use a small rubber or nylon mallet to shape pieces. Because the face of the mallet is small it is easy to see the progress being made during shaping, as well as direct blows to small areas that may need a bid more curving.
When a piece has several levels, such as with layers or metal or embellishments, the piece could be ruined if place face down in a well, as with these negative space Tropical Leaf earrings.