I need some help with an unusual building material. We have unsealed zinc countertops in bathroom, living room, and dining room and also zinc siding on some sections of the exterior of the building. All the countertops and siding are made from the same unpolished zinc that has a beautiful dark gray patina and is commonly used as exterior siding on commercial buildings.
We are finding that fingerprints, water drops, and many ordinary household products, including liquid hand soap, leave black or white marks on the zinc. I have tried a variety of products to clean the countertops including a neutral pH mineral oil (which works well to clean fingerprints) but have not found anything that works well as an everyday cleaner or to remove the black marks. Help!
Replies
I suspect that the marks you see are due to the oxidation and/or "reduction" of the zinc, due to various chemicals. Zinc is quite chemically active and is apt to be oxidized (resulting in a dark spot) or reduced (deoxidized -- resulting in a whitish spot) by various chemicals. These aren't stains but actual chemical changes to the zinc.
About all you can hope to do (besides keeping strong chemicals away from the surface) is to polish it up to remove the spots, then coat it with something that will prevent (to a degree) further chemical reactions. Over time, even through a chemical resistant coating (which should be renewed regularly) the metal will redevelop its patina.
The French use a lemon rind to clean zinc bar tops.
I would try it on an out of the way spot first, using a fine scotch brite pad to wipe it in evenly. After that you could rub in a light coating of mineral oil for added protection.
good luck.