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Zinc pest

Zinc pest, (from German Zinkpest), is a destructive, intercrystalline corrosion process of zinc alloys of poor purity.

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Zinc pest affects primarily die-cast zinc articles that were manufactured during the 1930s, 1940s, and early 1950s. In Germany, articles made from ZAMAK, a zinc alloy that also contains aluminum, magnesium, and copper, may be affected when produced during World War II and several years thereafter ^[1] Purer alloys were not available to the manufacturers as they were used for the war effort, or were just not on the market after the war. While impurities of the alloy seem to be the cause of the problem, environmental conditions such as warm humidity (greater than 65 %) may accelerate the process.^[2] Also, significant temperature changes can be damaging.

Affected objects may show surface irregularities such as blisters or pitting. They expand, buckle, tear, and in the end, crumble. The irreversible process will eventually destroy the object. Due to the expansion process, attached normal material may be damaged secondarily. Zinc pest is different from a superficial white oxidation process (“Weissrost”) that may affect some zinc articles.

Zinc pest is dreaded by collectors of old model trains, toys, or radios where the zinc die-cast process was used. Valuable items are rendered worthless but for their residual parts. Also parts of engines of older vehicles or airplanes and military medals may be affected. Fortunately many articles of the time period at risk show no signs of zinc pest and seem to be stable.

Articles made after 1960 are generally considered free of the risk of zinc pest. Use of purer materials and more controlled manufacturing conditions make it unlikely that modern zinc articles will encounter degradation by zinc pest.^[2]

Zinc pest is not related to tin pest.