This spiral staircase has eight balanced flights that give the load-bearing stringer a remarkable double-helix structure. It is a technical feat by a craftsman with a sound grounding in geometry, which probably explains why it entered the Conservatory's collections in the early 19th century. The work may have been the "masterpiece" of a skilful journeyman carpenter, but all the evidence suggests it was a model of the staircase in the main building at the Blendecques mill, later called the "Château Montreyan". Resembling the tidy architecture of a square pavilion, like the double helix staircase in the casting room of Buffon's forges it probably helped lend metal production a noble air. The Blendecques "tin mill" built in 1777 was probably designed in imitation of an English factory. In addition to showing off a carpenter's skills, this staircase is a splendid example of late 19th-century industrial architecture.