CLEANING, IRON STAIN REMOVAL, AND SURFACE REPAIR OF ARCHITECTURAL MARBLE AND CRYSTALLINE LIMESTONE: THE METROPOLITAN CLUB
FRANK G. MATERO, & ALBERTO A. TAGLE
Architectural conservation projects rarely afford the opportunity for the formulation of custom treatments such as those generally reserved for the conservation of related museum objects, especially in the case of stone. Often treatments must be selected and phased according to the product availability, weather, funds, and personnel charged with undertaking the job. Given the problems of scale and location, conservation treatments for buildings can involve enormous health and safety hazards that require compliance with a multitude of local, state, and federal regulations. And given the legal and contractual complexities, the numerous approvals required, and the high costs of any given construction project, commercial products and techniques are almost always favored over custom approaches, even in cases where the latter option may prove to be the better choice. Despite these often-difficult restrictions, responsible conservation can be performed provided a methodological approach is taken early in the identification and treatment of the issues.
The experiences of the Metropolitan Club suggest that successful large-scale noncommercial procedures are possible when conservators are included in the entire process, from project design to execution and evaluation. Metallic stain removal from ornamental and building stone, a common and difficult problem, can be treated effectively utilizing chelating poultices of ammonium citrate and ammonium hydroxide. This technique offers effective selective cleaning that is safe to the substrate, the operator, the public, and the environment and relatively inexpensive and easy to apply. Moreover, such techniques allow for the controlled removal or reduction of metallic staining, thus permitting surfaces to be cleaned while at the same time retaining and modulating acceptable levels of surface patina.