Factors causing deterioration of frescoes within a medieval church in Malta and a proposed solution

Abstract

The fifteenth century Church of the Annunciation at Hal Millieri hosts a cycle of frescos which are unique to Malta. Concern for the conservation of these frescos prompted a long-term study which included monitoring of the internal micro climate of the church and chemical and mineralogical analysis of samples taken from its fabric. Salts, mainly, sodium chloride and nitrate, were found in the lower courses of the limestone walls. Erratic fluctuations in the relative humidity i nside the church occasioned crystallization of these soluble salts with damaging effects on the frescos. Sealing off small windows in the little-used church caused the relative humidity to stabilize above 75¾. This simple measure has eliminated the dissolution/crystallisation cycles and proved to be sufficient in resolving the problem of deterioration.