In the Museum of Art and History, Geneva, there is a rich collection of old scientific instruments comprising objects dating from the 17th century, including: microscopes and astronomic, geodesial, and meteorological measuring implements. The conservation of these objects is always a special case which has only limited traditions. Special problems considered include potential exhibition, cleaning, functional state, analytical possibilities, and authenticity. The authors especially consider the conservation of various materials within these highly sophisticated composite objects. Special attention is paid to the protective lacquer and cleaning utensils.