Case studies in the determination of the original surface limits of the ferrous armour of the order of St. John, Palace Armoury, Malta

Abstract

Ferrous heritage artefacts either from a burial environment, or in an indoor museum, can be either totally or partly masked by (or even comprised of) corrosion product (CP) layers. Some CP layers reduce surface legibility and corrosion resistance, and possibly contain altered traces of original surfaces. The correct amount of corrosion product cleaning required for all artefact materials and environments is not yet a fait accompli... As Bertholon suggests, " ...we must question our attitudes about the cleaning of other archaeological or museum objects" • The way the corrosion products evolve on mid-late Early Modem Period wrought iron and low-carbon steel in an atmospheric environment, and any capability of retaining the limit of the Qriginal surface (or limitos after Bertholon), is the topic of this dissertation. This experimental research diagnostically determined the presence of the limits in atmospherically corroded steel to indicate an appropriate level of CP removal during conservation treatments of historical wrought ferrous artefacts. Specific attention and adaptation of the findings was made to a historically accessible and atmospherically exposed collection: the partly corroded 16th -17th century northern Italian-style wrought iron and low-carbon steel munition armor of the Order of St John, Palace Armory (PA), Malta.