Ash cupels were widely used in early modern Europe for small-scale refining of noble metals in artisanal workshops, mints and assay offices. The manufacture and use of cupels display considerable variability from context to context, which poses both challenges and opportunities for modern investigation. Here, we present the analytical study of an unusually large cupel recovered from castle of Middleburg-in-Flanders (Belgium), probably dated to the sixteenth or early seventeenth century, which we discuss in connection to historical sources and other archaeological finds. We demonstrate that the cupel was made of bone ash mixed with a small fraction of another calcareous material, and most likely used for the refining of silver heavily debased with copper. We illustrate simple methods to investigate the manufacture of cupels and the nature and amount of metals being refined, as well as approaches to assess and discuss cupellation performance in archaeological contexts.