Despite its short history, the royal-university collection grew significantly: from 542 casts purchased by Stanislaus Augustus to over 750 sculptures finally gathered at the University. For years, agents purchasing artwork for Stanislaus Augustus, university professors and museum directors tried to cooperate with numerous casting workshops throughout Europe which produced copies of prominent ancient works of art. Plaster casts were especially important to the University of Warsaw. For a long time, they functioned as ars, a priceless collection presented to the wider public at the Column Hall, as well as educatio when they were utilized as a basic educational tool for students of painting, sculpture or architecture. This paper is devoted to the markings used by casting workshops that manufactured some of the surviving casts. Such designations allow not only to track contacts with European workshops but also to determine the origins of particular works and the exact time of their creation or the name of the caster.