Did you know? Anti-microbial properties of copper and brass—those brass knobs may actually be good for you!

brass and bronze3_edited-1We have long appreciated the old brass and bronze knobs around here for their beauty and durability. Just remove a little spilled paint, give them a bit of a polish, and they will glisten like new—or almost new, depending upon how much polishing you do. Only recently has a Wikipedia article on the subject of the possible anti-microbial properties of the metal come to our attention. Without repeating the entire write-up verbatim, it seems that previous generations were well acquainted with the desirable properties of copper and copper-based alloys (such as brass, bronze and cupronickel). Going back centuries, before the very concept of microbes had developed, it was observed that water in copper pots or conveyed in copper would be of better quality (for example, no slime formation) than water carried in other materials. Fast forward to recent centuries, and there have been numerous scientific studies conducted to test this very concept. The results have shown, for example, microbes of the E. Coli bacterium will show a 99.9 percent kill rate within 1 or 2 hours of contact with copper. Those same microbes will survive on stainless steel for weeks. (Oddly, stainless steel is and has been one of the most common touch surfaces in the healthcare industry.) It’s worth noting that these results were on surfaces of solid copper—most copper-based alloys will requires somewhat longer times to achieve their anti-microbial properties. Brass, most commonly used for doorknobs over the years, will require anywhere from 1 to 4.5 hours to achieve the same kill rate. With all of the alloys, the rate is affected by air temperature and the amount of copper in the alloy (i.e. the more copper, the better it works). It has to be noted that a protective layer of lacquer, applied to reduce the need for constant polishing, will negate the health benefits of the metal entirely. Clearly, the microbes need to be in direct contact with the metal to be gradually eliminated. With all of this in mind, why wasn’t all hardware simply made of solid copper? Aside from the visual appeal of the golden tones found in brass or bronze, copper as a metal is fairly soft. The addition of zinc, tin or nickel or other metals serves to provide a stronger alloy for more robust use. Given the stresses of repeated twisting of a doorknob on its steel spindle, the weaker copper would gradually loosen its grip and begin to twist and shear. The stronger brass and bronze would retain their shape longer, and provide a more enduring product. This isn’t to ignore the visual appeal of copper in its own right. Brass, bronze and steel were frequently copper plated to give the rich pink-hued sheen of copper, but this was more to enhance its visual appeal than to provide any sort of health benefits. Today we can appreciate this option for a whole new reason!