This object is the remains of a brass porthole ring measuring 250 mm across with a brass rim 28 mm wide. It is thought that this frame would have been on the outside of the hull of the vessel while an internal frame on the inside of the vessel would have contained the glass element and a hinged deadlight (a metal plate that was both a curtain and a reinforcement against heavy seas). Portholes have been used for centuries to allow light and ventilation to enter the lower, darker levels of vessels and in some early cases, as a means of seeing out of a submersible. Portholes are watertight and are generally crafted from glass, secured within a metal frame that is then bolted to the vessel. The popular metals that are used to create the frame of the portholes are bronze and brass because these metals corrode less in saltwater. This object is the remains of a brass porthole ring measuring 250 mm across with a brass rim 28 mm wide. It is thought that this frame would have been on the outside of the hull of the vessel while an internal frame on the inside of the vessel would have contained the glass element and a hinged deadlight (a metal plate that was both a curtain and a reinforcement against heavy seas). Portholes have been used for centuries to allow light and ventilation to enter the lower, darker levels of vessels and in some early cases, as a means of seeing out of a submersible. Portholes are watertight and are generally crafted from glass, secured within a metal frame that is then bolted to the vessel. The popular metals that are used to create the frame of the portholes are bronze and brass because these metals corrode less in saltwater. A RDF representation of MAS-F100108 2017-08-23T08:38:12+01:00 2018-05-08T08:40:10+01:00 MAS-F100108 MAS-F100108 GB en-GB The Trustees of the British Museum The Trustees of the British Museum 1 The period from for the object http://purl.org/NET/Claros/vocab#Thumbnail Attribute as courtesy of the British Museum A thumbnail image of MAS-F100108 With finder MAS Created by MAS Richard Endsor Richard Endsor Identified by Richard Endsor V L Identified by V L Incomplete 28. Width 250. Diameter 3. Thickness By Attribution 3.0 Yellow metal Primary material of object Attribute as courtesy of the British Museum A full resolution image of MAS-F100108 Classification of object