The Numismatic Collection of the Kunsthistorisches Museum (KHM) Vienna has a large collection of ancient Greek bronze coins. A considerable number of these leaded bronze coins show progressive corrosion, almost certainly as a result of storage conditions in wooden boxes over many decades. These coins are in need of urgent conservation and stabilisation, which is currently addressed by transferring the objects to new storage containers. In parallel, a research programme is carried out to understand the nature of the corrosion processes which are largely unexplained. Neutron diffraction studies are part of the scientific analysis, for determining the alloy compositions and mapping corrosion products in the interior of a coin. The results will help working out a suitable restoration and preservation programme.