When I first started collecting coins over 50 years ago, to clean a coin was considered a major sin.
Erasers contain course abrasives which badly scratch the coins.
They used a tooth brush and powdered toothpaste, which contained finely ground baking soda or they used regular baking powder with a tooth brush. Many used silver paste rubbing compounds. All these compounds are highly abrasive and tear up the surface of soft metals, such as gold, silver, copper, and other mallible metals that coins are made of. Along with watching television, treasure hunting became a national pastime in America. Three or four monthly magazines were published on treasure hunting.