What is the black dust that forms on antennas?

If your antenna has been on the roof for a while you might notice that it’s covered with a fine black dust. This may worry you, it may even keep you up at night. But rest assured, it’s not a terrible thing and believe it or not it’s better to have that layer of dust than not have it. It may seem unsightly at first, but when you realize what’s really going on, you’ll learn to like it.

It’s a perfectly natural byproduct

The black dust on your antenna is aluminum oxide. All metals have a tendency to combine with oxygen to form another substance. In the case of iron, iron oxide is not as strong as regular iron, and you’ve seen it yourself. The common name for iron oxide is rust. You’ve seen how a rusty piece of iron can fall apart easily. However, not all oxides are the same. Silver oxide (otherwise known as tarnish) is ugly but harmless, and aluminum oxide is fairly similar.

Some oxides are a problem…

Generally oxidation is a problem. In many metals, oxidation makes things worse because oxidized metals aren’t as strong as pure metals. This is certainly true with rust and that’s why rust is such a big problem. Oxidized metals generally don’t conduct electricity as well as pure metals, either. That’s the biggest reason you wouldn’t want an antenna made of copper (other than the price, of course.) As that copper oxidized it would work much worse.

Aluminum oxide is different

The black aluminum oxide coating on an antenna doesn’t affect the antenna’s ability to pick up signal, because aluminum oxide is roughly as conductive as regular aluminum. Unlike rust, once an oxide layer forms on an aluminum surface, the oxide itself acts as a barrier to stop more oxides from forming. So it’s actually protecting the antenna from becoming corroded. Common silver polish will take off the coating, but repeatedly removing it will eventually weaken the aluminum. That’s the amazing thing here. A fine layer of oxidation on an aluminum antenna doesn’t hurt reception. It actually protects the antenna. Go figure.

So why aren’t they sold that way?

Given that aluminum oxide is harmless and actually prevents further corrosion, you might ask why all antennas aren’t shipped “pre-oxidized” with the fine black coating already in place. Blame that, I suppose, on Americans’ predilection for shiny things; in the chrome-plated world of 1940s and 1950s USA, it simply wouldn’t do to send you something brand new that was already dull grey and black No, a shiny new antenna is what you wanted and that’s what you got. Not to mention, pre-oxidized antennas would cost more to make because you would have to actually do the oxidizing.

Bottom line though… don’t worry about that fine black dust. Believe it or not, it’s your friend. It will help your antenna last longer even if it does look a little dreary.

Ready for a new antenna?

If you choose the right antenna, you’ll generally be able to use it for decades. Some folks use antennas made before they were born, because that’s what came on the house. But, sometimes, it is time for a new antenna. The old one could become damaged or might not receive today’s broadcasts as well as it got older ones. When you’re ready to buy, I hope you’ll check out the great selection at Solid Signal. 

About the Author

Stuart Sweet
Stuart Sweet is the editor-in-chief of The Solid Signal Blog and a "master plumber" at Signal Group, LLC. He is the author of over 7,000 articles and longform tutorials including many posted here. Reach him by clicking on "Contact the Editor" at the bottom of this page.