Balneum Mariae (also known as Mary's Bath, water bath, bain-marie or double boiler) is a process of controlled heating in a pot with liquid, usually water, aimed at heating substances in controlled conditions (in terms of both time and temperature) or keeping them warm over longer periods of time. In fact it limits the maximum temperature of the substance in the main container to the boiling point of the liquid in the second boiler.
As the name indicates, the process has been attributed to he alchemist Maria Prophetissima or Mary the Jewess (3rd c. A.D.) The process was nevertheless known before, during the Roman period for example, and became common in cooking, industry, chemistry and pharmacy.
|Alchemical balneum Mariae from Coelum philosophorum, Philip Ulstad, 1528|
Discover more about the inter-twined history of pharmacy and alchemy by visiting the temporary exhibition at the History of Pharmacy Collection in Cluj-Napoca.