Piano hammers are like your shoes, they wear out with a lot of use. After many years of hitting a string your felt hammers will form a hard flat surface at the strike point. This creates a tinny, harsh tone and a piano that is difficult to control. Hammer carding, or reshaping, is the process where a technician will sand all of the hammers down so that the hard flat surface is gone and the shape is similar to a new hammer. I carded the hammers on Lone Jones‘ piano the other day and it made a world of difference to the sound. This old upright became so much more mellow with a wide range of colour and dynamic possibilities. Lone was so happy and felt a lot more comfortable playing her instrument.