“Superficial corrosion can be caused by environmental factors such as exposure to corrosive gas, air pollution, off-gassing from an enclosed wood case, exposure to water, salt deposits (from hands, for example). There can be a multiplicity of causes. Pot metal, by definition, is a mixture of metals. The composition of pot metal varies—corrosion can be due to inherent vice—meaning the combination of material in any given piece can lead to corrosion without the assistance of other agents of deterioration. “
Steps to prevent further corrosion:
• Display away from acidic materials (i.e. unfinished wood enclosures)
• Prevent exposure to water or corrosive liquid. For example, liquid cleaning products will cause corrosion. Any household solvent, furniture wax, or cleaner will accelerate deterioration.
• Minimize handling. This will limit exposure to salts, oils, and moisture. When handling, use nitrile gloves (i.e. not cotton gloves). Or, at minimum, use freshly washed and dried hands.
• When not on display, consider storing in acid-free tissue and placing in a plastic bag with corrosion intercept or in an acid-free box. Companies like University Products and Metal Edge have such materials for purchase.
• Dust with a soft bristle brush
• Sometimes pot metal objects have a coating. If a coating is present and corrosion is evident, consult a conservator.
• If the corrosion is minimal and superficial (meaning, it does not extend into the interior of the object) and there is not coating present, it may be possible to address the corrosion with mineral spirits. A small, discrete spot test should be completed. If there are any questions as to whether a coating is present or about the extent of the corrosion, a conservator should be consulted.
Sounds like we should put away the vinegar and utilize mineral spirits for cleaning spot corrosion on metal buildings. I looked at the ingredients for mineral spirits and vinegar to see if there is something similar about them, but nothing is listed. Perhaps they are just very mild acids? The mineral spirits can did say to protect your eyes and wear gloves when using. This story in The Washington Post described the differences between preservation, conservation and restoration. The American Institute for Conservation of Historic and Artistic Works (AIC) also has information about caring for metal objects:
“One of the sources of damage to metal is improper handling and carelessness. Oils and acids that are continuously secreted through human skin are deposited on metal surfaces during handling, where they cause corrosion and pitting. Metal objects should always be handled with clean, white, cotton gloves, or nitrile or vinyl gloves with a pair of cotton gloves over them to further prevent sweat from passing through to the object. If items are handled with bare skin or are used, as in the case of tableware, they should be carefully cleaned before storage or display to remove these deposits and prevent corrosion from skin acids and oils.”
Hands & humidity, dust & dirt, water & whatever is a collector to do? Does this mean we should store all of our collections in acid-free boxes in a temperature-controlled environment underground and never touch them with our bare hands or breathe on them? Perhaps, if you want them to last forever and they are precious one-of-a-kind rarities. Personally, I get the most joy from my collection by seeing it everyday. Yes, they collect dust. Yes, I pick them up a lot and expose them to my salty hands. But, I will protect them from most hazards when I can. Some things to think about: Do you display your buildings on unfinished or unpainted wood? Gas from the wood could affect your buildings. How do you clean your metal souvenir building replicas? Do you have any tips to share with fellow collectors? Let us know via the ‘comments’ link below.