As bronze and brass cased watches have become more common, we are learning more about how they behave over time, By and large, they have aged exactly as we consumers expected, picking up nicks and scratches with normal wear, and developing a mottled brown patina as the metal oxidizes. Some adventurous Patina Scientists have treated their watches with liver of sulfur, vinegar, ammonia, or just plain hard boiled eggs to accelerate the process and tailor the results. The vast majority of the time, that is about all there is to report, but every now and then, things get weird.
Usually, the weirdness is fairly predictable. I have a number of bronze and brass watches in my collection so I have had plenty of opportunity for field tests. I am naturally sensitive to metals. Nickel and cheap gold plating will eat my skin. I have only had a problem with bronze when I sweat, which can cause a reaction where bronze buckles touch my skin, ranging from a harmless greenish stain to an itchy red rash. I have learned to be careful on hot days and to be aware of whether the metal makes contact with me. On most watches, stainless steel casebacks and thick straps ensure the bronze does not touch my skin at all.
I allow my watches to patina in their own time, letting the air and the occasional dip in the ocean work their magic. I have never seen any evidence of damage from the oxidation, which is why I so surprised when a reader sent me pictures of a brass Maranez Layan that showed significant etching. He reported that he had purchased the watch new a year ago, accelerated the patina with two or three cider vinegar fuming sessions and took it on some trips to the beach. Later, when he cleaned off the patina, he discovered the problem. The first picture shows the watch before he removed the patina. The second and third show what was revealed underneath. The same reader also sent pictures of a bronze Makara, owned by another person (fourth picture) that showed the same kind of surface damage after similar treatment.
I did not think that vinegar or seawater could have such a dramatic effect. My first thought was that it might be a problem with the metal itself, but this made no sense. These are two different cases made from two different metals. Moreover, if there was a bad batch of bronze or brass at a factory, it would affect entire production runs across several watch companies, not just a single case here and there. Baffled, I reached out to Maranez and Makara for their responses.
Maranez was less than excited about the vinegar fuming, saying, "If you torture the material to force a patina, you can't complain when it gets scars." I can't disagree. While most acceleration techniques are benign, chemical treatments are well outside the normal definition of wear and tear. However, they were more concerned with seawater exposure, noting the corrosive effects of salt, and recommending owners rinse their watches in fresh water after those trips to the beach.
Makara offered a slightly different scenario, positing that the damage may be the result of bronze disease, a destructive process caused when chloride salts from seawater or soil react with the copper in the alloy to form hydrochloride or hydrosulfuric acid in the metal, manifesting in a fuzzy or powdery green or blue-green corrosion. These patches differ from the usual patina in that they are brighter, raised, and can be scraped off with your fingernail. Unlike benign oxidation that serves to protect the underlying metal, bronze disease attacks it. Worse yet, the process is self-sustaining, eventually destroying the affected object unless it is thoroughly decontaminated. It is a reasonable explanation but as neither of these watch owners reported the "bloom" associated with bronze disease, the mystery persists. Regardless, Makara said they would be willing to work with the customer on a possible resolution, even though the problem would appear to be environmental, and not a covered manufacturing defect.
So bronze and brass alloys can mess with your skin and are subject to malignant corrosion. Is it still a worthwhile watch case material? It is to me. Heck, I'm wearing a bronze Zelos Abyss (reviewed here) while I'm writing this. There are the risks to owning a "living" metal but downsides are rare and the warm, aged look of these watches can't be beat. Still, if you are looking to buy your first bronze watch, you should know that its unique character may not always be predictable.
Photos courtesy of Nick Lessells (Instagram @nicklessells).