Hamsterley Colliery Derwentcote steel furnace (The Cone)

The Hamsterley Colliery Derwentcote steel furnace, known as The Cone, is a Grade I listed steel-making furnace from the first half of the 18th century, specifically designed for the cementation process. It is constructed from coursed sandstone rubble with some ashlar dressings and had no roof at the time of the survey. The structure is one storey high and consists of four bays, with a prominent high cone located on the second bay of the furnace.

Three buttresses support the cone, and there are small square openings between the buttresses, with the one on the right being blocked. The furnace features rough wood lintels over a partly-blocked door to the right and an empty window in the first bay. The fourth bay has a stone sill for a window, which has a ruined lintel and an Ordnance Survey bench mark. The return gables are intact, with the left gable featuring a large buttress. The rear elevation displays three buttresses supporting the furnace; the central buttress is truncated, while the left is integrated into a later one-storey, one-bay outshut.

The high stone cone has two square flue openings at the top of the ground floor and contains a square opening with a rebated stone lintel and jambs, along with a plain stone sill. Inside, there are iron lintels over funnelled entrances to the cone, featuring an inner brick pointed arch on the right and a stone lintel on the left, both flanked by buttresses.

This furnace is the only complete surviving example of a cementation furnace in England. At the time of the survey, it was empty and derelict and is recognized as an Ancient Monument in Guardianship.