Jürgen Küchler's favourite piece: a filigree Venetian wing glass. "In the 12th century, Venetians succeeded for the first time in washing the glass clear like rock crystal," the museum's advisory board member reports. A special challenge, because glass naturally has a colour cast. Neutralising the green tint in the glass was only possible with the help of reddish manganese, the so-called glassmaker's soap.