THE CONSERVATION OF AMERICAN WAR MEMORIALS MADE OF ZINC
CAROL A. GRISSOM, & RONALD S. HARVEY
Separated joins and broken metal are repaired with either metal or synthetic plastic materials, although neither is ideal. Chief among the metal crack repair techniques is soldering with lead-tin solder. Pouring zinc into joins has been done recently for repair of a white-bronze Confederate soldier in Suffolk, Virginia, imitating the original joining technique (Spring 2001). Metal repair techniques may prove more durable than plastic repairs, but pristine surfaces are required for good adhesion of the new metal, and a pristine surface necessitates harsher cleaning than may be considered desirable by conservators. Repairs using polyester or epoxy resins reinforced by fiberglass cloth or the like are less invasive. In Austria, silicone-based fillers have been used where movement may occur and strength is not important (Krebs 2002). The disadvantage is that synthetics have limited life spans when exposed to outdoor environments.
When distortion of cast zinc is not excessive, the best course may be to leave it without treatment, as remediation may result in breakage. When the only alternative is recasting, on the other hand, reshaping might be considered. Bulges of a large, badly distorted section of a white-bronze monument were recently placed upward, and heat and pressure were applied until the metal had settled into its original plane (Polich 2001). Cracks opened in the process, however, underlining the fact that such treatment is not without risk. Sheet-zinc distortions, by contrast, can be removed with minimal potential for breakage after the metal has been heated using propane torches or the like. Hammering against wooden or metal forms has been found to be useful.
Losses are replaced with zinc or aluminum castings as well as plastic composites. Missing areas have also been cast in place by pouring zinc from the inside into molds placed on the exterior (Holm 1994). Since replicas of soldiers are relatively common, a missing part may often be molded from an intact statue.
Cast statues usually do not need much additional support, but large white-bronze monuments often require installation of expensive stainless-steel armatures. The support of individual statues may be improved by installation of simple vertical stiffeners made of zinc or stainless steel inside the self-base. Armatures for larger zinc monuments, on the other hand, require design by an architect or engineer and fabrication by a skilled welder. The statue itself is usually supported by a plate underneath its base, in turn fixed to the armature. Stainless steel should be used for these large armatures because of its strength and corrosion resistance. Type 316 is recommended because it has the highest corrosion resistance of standard stainless steel, but type 304 is sometimes used when cost is an issue. Before work begins, foundations may need to be upgraded. Armatures can then be installed, usually in one of two ways. In the first instance, they are attached inside each section at a workshop off-site, and the sections are afterward assembled and bolted together on-site. In the course of treatment completed at a foundry, bronze plates have been soldered to interior surfaces of sections of a white-bronze base to provide surfaces to which stainless steel armatures could be easily welded (Polich 2001). A second approach is exemplified by treatment of the Biddeford Civil War Monument (see figs. 6, 7). The soldier was removed, providing sufficient access to the interior. Each piece of the new armature was then arc-welded in place by a man working inside the monument. This procedure had the advantage of not requiring the monument to be disassembled, and it could rest on the new armature without being fixed to it. Gaps between the stainless-steel armature and zinc were filled with high-compression-resistant, two-part epoxy putty (Pliacre), isolated with Teflon tape. When large monuments are reassembled or new armatures installed, compromises may be required. Leveling the Biddeford Civil War Monument improved the monument's overall appearance but left a substantial gap between the statue's base and the element below, subsequently filled with Pliacre (see figs. 6, 7). The bottom of monuments should never be sealed because trapped moisture can cause intense corrosion of zinc.
Concrete does not usually adhere to zinc, and it can be removed relatively easily from simple forms like self-bases. Concrete is far more difficult to cope with when it is locked in place mechanically, as when poured into large white-bronze bases. Thick joining deposits also make white-bronze monuments difficult to cut apart at the corners, where they would otherwise be least damaged. So much damage would likely occur in the process of concrete removal that such monuments may not be repairable at all.
Removal of powdery corrosion products is necessary when new paint coatings are applied to zinc soldiers. Blasting with walnut shells and other abrasives has been used, as has washing accompanied by stiff brushing. Application of corrosion inhibitors has been proposed, but experience with their use on zinc is limited (Riederer 1997). The best medium for painting zinc remains unclear. Laboratory stress tests on air-abraded surfaces have shown best performance by acrylics, polyurethane resins, and a mixture of urethane, alkyd, and acrylic resins (Mottner 1998). Nevertheless, coatings that failed laboratory tests have performed well in practice, and documentation of paints in actual use in Europe since 1985 may soon provide better evidence of durability (Riederer 1997). As the art of bronzing has been largely lost, attempts to re-create bronzed finishes have often been less than satisfactory. Commercial bronze paints are usually too glossy, uniform, and plastic-looking (see fig. 3c). Recently a nuanced bronzelike surface was created for the soldier in Pottstown (see fig. 2). A toned acrylic topcoat was mixed with micaceous pigments (to simulate copper flakes) and applied locally to achieve lights and shadows (Kwart 2001). Application of silver-colored metallic paint in a misguided imitation of zinc's color occurs surprisingly often, even under the supervision of conservators. Historically such paint would never have been applied, however, and the practice should be avoided. Copperplating, too, is not advisable, as it requires aggressive cleaning and is unstable, especially outdoors.
White-bronze surfaces present different problems, since corrosion products were considered desirable by the makers and the monuments were not meant to be painted. Surface treatment is often called for to minimize graffiti and integrate repaired areas, but application of any coating precludes the intended stonelike appearance of sandblasted, corroded metal. If graffiti are the only issue, dark scratches can be retouched with light-colored paint until corrosion products are formed. If painting is deemed essential, application of matte gray paint may produce a result closer to the intended appearance than a clear coating, although paint has the disadvantage of increasing maintenance.