The best material would be Cor-Ten steel, which develops a coating of rust which becomes passive. Originally developed as a structural steel that would not require sandblasting/painting. May be difficult to obtain in small amounts. Patina on virtually any other metal will require coating of some sort to maintain a steady state, and the coating is subject to breakdown. What about plaster, concrete or ceramic molds/applique?

Greetings folks. I have a ritual but I'm getting too old and tired to continue it. Every year I strip off the discolored top layer of my Brazilian Cherry (Massaranduba) hardwood deck and refinish it. I had the misguided notion that it would last forever and be low maintenance. It may last forever but it is far from low maintenance. I have come to view it as a very expensive mistake. I have tried many different coatings but always with the same result. The beautiful cherry color soon turns to a drab brown and stays that way until I get the time and energy to start the process again. The unshaded northern exposure in the northeastern U.S invariably takes its toll. Currently I power wash the deck at pressures that would tear up a pine deck and apply a different coating in the hope that this year will be different. I have tried CWF, that was bad. For a few years I was using Penofin Marine Wood Oil. In my desperation I confess that I smuggled it into my state. Then for a few years I mixed my own; a concoction of Boiled Linseed Oil, Turpentine and Paraffin or Varnish. All because I wanted to try preserve the appearance of the natural wood. Now I am starting to consider what was previously unthinkable: a solid stain. There I said it. I know this is a very 1st world problem and you would within your rights to laugh at my perceived problem but if you have a opinion of what I should do, I'd like to hear it. Solid stain or something that I haven't tried? Thank you.

Not exactly a robe hook for me, but something I was determined to use for something else but was concerned about the original finish. The original finish was Satin, much like your robe hook (which I love!). No complaints, worked like a charm. Since then I've used Krylon Satin Clear on sooooo many things around the house. Protects the item, easy to apply, almost goof-proof and very inexpensive. And because it's a Satin finish, doesn't make the item shiny or plastic-looking. A Bunny wall plaque. (I can take a pic and post it if you'd like to see how it turned out). It is a smaller, sorta round plaque with lots of detail but because it's a smaller plaque, I wanted to make sure the detail would show. Tried it all lots of walls. Never quite liked where I tried. Don't even remember what sparked the idea but I decided to use the plaque as a trivet for either utensils while I'm cooking or to set my hot tea pot on while I get the cups ready for tea. Made sure the plaque was super-clean and dry. VERY LIGHTLY from about 3 ft. away I sprayed the plaque...VERY LIGHT FIRST COAT. I let it dry for several hours. Second VERY LIGHT coat. Dry. Third light coat. I've had the plaque clear-coated for awhile now and I don't have ANY yellowing, no flaking of the clear coat, no damage of the plaque or clear-coat from the hot tea pot and I've washed the plaque many, many times in the sink with dish soap and a teflon sponge to get dried stuff off that got dripped on it. Here is a link that might be useful: Krylon Satin Clear

You can wax them when you're done cleaning. Carnauba car wax is pretty good on metal and won't hurt anything. (Don't get the type that buffs out scratches.)