What is "hammerscale"

n. A small fragment dislodged from iron during forge.

__FORCETOC__ Hammerscale, also written hammer scale, is a flaky or spheroidal byproduct of the iron forging process (for modern equivalent, see mill scale). Hammerscale is almost universally recovered from archaeological excavations in areas where iron ore was refined and forged. Hammerscale’s magnetic character also aids in its recovery and in mapping larger features by means of magnetic susceptibility surveys. Hammerscale can provide vital information about an archeological site such as the function of the feature.