Just to elaborate on Jim's reply, picking oakum involved unpicking old ropes to produce hemp fibres which were then sold for caulking the hulls of wooden ships. The rope would usually be hemp rather than flax. As the ropes were often coated with tar and had seen hard use, and the picking was done with the bare hands, this was hard work and in prisons counted as hard labour alongside the treadmill and stonebreaking. Residents of poor houses were also expected to work, and this too might involve picking oakum.

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Portsmouth Asylum