The proposed measurements aim to determine the behaviour of the structural parameters of iron-phosphorus alloys as a function of P-content, in order to have a reliable calibration curve linking the ferrite lattice parameter value to the elemental phosphorus content of the alloy. The high penetrating power of neutrons permit the totally non-destructive analysis that is required for intact, dense cultural heritage objects such as bloomery iron artefacts. Once the calibration curve is determined using experimentally produced standards, we can examine previously collected and future neutron diffraction data-sets from archaeological iron objects, and calculate the bulk phosphorus content of the alloys. Apart from carbon, phosphorus is the most common alloying element seen in iron that was made prior to the Industrial Revolution. We request 4 days of beamtime on INES to analyse 12 standards.