Two lead foundation plates dating from 1711 and 1730 respectively have been found in the collection of the Société académique de l’Oise. They originate from a building constructed by Lucien Danse, a merchant and later modified by his son, in Beauvais (Oise) at the beginning of the 18th century, and destroyed by bombing in June 1940. This article describes these two foundation deposits, comparing them with other time capsules from the 18th and 19th centuries. By comparing various archival sources from the 18th and 20th centuries, the work of historian Pierre Goubert and a partial reconstruction of the buildings - dwelling house and laundry - has been envisaged. Finally, the text ends with a brief evocation of the Danse family, the wealthiest of the Beauvais merchant families, specialized in laundry and the national and international linen trade.