Since the Renaissance, plaster casts have been the most important medium for the three-dimensional reproduction of historical sculptures. They experienced their golden age in the 19th century, when huge plaster collections were created and the casts were in some cases even equated with original works of art. In the early 20th century, plaster as a material was temporarily discredited - not least because of the unsightly appearance of older, dirty casts - and many important collections were destroyed. Plaster is an ideal casting material, but it is sensitive to dust and difficult to clean - a problem that was vividly discussed in public and among experts already in the 1870s. At that time even international conferences were held on the problem of plaster cleaning and conservation. On the occasion of the 250th anniversary of its cast collection, the Archaeological Institute of the University of Göttingen resumed this debate and made it the subject of an international conference attended by curators of archaeological university collections, art historians, materials scientists and restoration experts from eight countries. The 23 conference contributions in German and English published in this volume explain the concepts for the presentation of greyed, material-imitating and white-coated or over-sprayed plaster casts from the context of the respective collection history. Cleaning methods presented in case studies range from the use of various sponges and pastes or gels to laser applications. Different procedures for removing secondary paint layers on plaster casts are also discussed. The examples stem from numerous university cast collections, but also from large European museums, academies and libraries. Not only casts of historical sculptures are considered, but also artists’ original plaster works from the 19th and 20th centuries.