Corrosion Resistant
Resisting the Rust
"Corrosion resistant" means a metal substance has been specially treated to resist surface oxidization (a.k.a. rust). There are three main ways to accomplish this during manufacture: galvanization, by which the metal is treated to resist corrosion and weather exposure; electrogalvanization, which provides a smooth surface to the metal along with some corrosion resistance; mechanical galvanization, which increases the corrosion resistance by depositing more zinc; and hot-dip galvanization, which turns the metal a dull gray 'spangled' color and grants very high corrosion resistance.
As an example, let's look at house number signs. These are often mounted using nails or brackets, or may be sold inside a metal frame, all of which must be protected against rust. One of the above methods might be used, or the metal can be painted with a rustproof layer, which is common.
Caring for the Metal on House Number Signs
House number signs are a ubiquitous outdoor decoration. It's not unusual to see house number signs in well-to-do neighborhoods, as well as vacation or resort areas. All of these house number signs must be able to withstand the elements, all year long, without cracking, warping, or fading.
This requires some foresight on the part of the house number signs manufacturer. First of all, they must decide how to rustproof the frames of the house number signs, or whether to do so at all. Some manufacturers don't, making it the homeowner's responsibility to rustproof their own house number signs!
Other hardware used to hang house signs, such as top hooks and S hooks, should be rustproofed as well, if they aren't already. Many hardware stores sell these types of pieces pre-painted with a metal alloy that guards against rust. However, if the surface becomes scratched or starts to peel (as may happen with friction over time), the hooks should be immediately repainted or replaced. Rust on top hooks or S hooks is a sure sign that your house number signs are the next to go.
The Final Step
If you do discover rust forming on the metal hardware around your house number plaque, it isn't the end of the world. A piece of aluminum foil dipped in water can be used to literally scrub off the rust. Once the rust has been removed, paint the exposed metal surface with a rustproofing layer of paint. If the metal in question is not a frame but a piece of hanging hardware for house number signs, consider applying a layer or two of marine varnish. Varnish seals house number signs against the elements, preserves their brilliant colors, gives them an alluring sheen, and makes them virtually weatherproof for years.
It isn't difficult to maintain home signs (or any other outdoor decoration, for that matter) while protecting them against rust as well. You need to be vigilant, and you need to react immediately when you see rust, but the threat itself can be minimized almost into non-existence.