Tired of grounds in her teeth, Melitta Bentz punched holes through the bottom of a metal cup, cut a disc from the blotting paper in her son Willy’s school exercise book, and poured boiling water through it. She registered the result as a utility model at the Imperial Patent Office in June 1908 — among the first women in Germany to protect an invention of her own — and had her own company by that December, on 72 pfennigs of capital. The stone went up in Trachau in 2020, seventy years to the day after she died.