The man who knows so much

摘要

Your tally is 150-plus published answers since 1996. How did it all start?rnOne of my earliest questions was about why it is harder to erase old pencil marks than new pencil ones. It just intrigued me.rnSo why is it harder to erase old pencil marks?rnI suspected there were two effects at work. Pencil graphite contains wax, and while this wax is still soft, minute particles of graphite get absorbed into hollows in or between paper fibres.