Do Brass Doorknobs Disinfect Themselves?

For centuries┬ábrass has been the metal of choice for door knobs. In recent years design trends have shifted to brushed nickel coated steel and recently to black coated steel. But there may have been a reason brass was popular for so long … it actually kills bacteria. As many infections can be spread by door knobs, it’s interesting to note that a brass knob (unvarnished) will disinfect itself in about seven hours. Steel, Stainless Steel and Aluminum knobs will never disinfect themselves.

This effect was discovered by Swiss botanist Carl von Nageli in the 1890’s and is known as the Oligodynamic effect. He studied how metal ions, even in low concentrations, are toxic to living cells and microorganisms, concluding that the metal ions of silver and copper and copper alloys interfere with their metabolism.

You might think that shiny stainless steel door knob would be a better antibacterial than a grungy-looking tarnished brass one. Think how many times you have seen stainless steel knobs in hospitals, they must know a few things about germs, right? In fact, brass (being a copper alloy commonly 65% copper/35% zinc) is germicidal. Stainless steel (being an iron alloy (88% iron/12% chromium) is not.

If you want to get the most disinfectant benefit from your brass door knobs you have to remove the coating that manufacturers put on them to keep them shiny. Paint stripper will do the trick. You’ll have to polish once in a while if you want them to be shiny, but they also look very nice if you let them age to a beautiful patina. Here’s to beautiful brass.