Aluminium ring leaves blue mark on one finger

March 30, 2024 11:34 AM

I have a ring made out of recycled aluminium. I wear it on the ring and middle fingers of each hand randomly. It leaves a dark blue, ink-like mark only on the top side of my right middle finger that comes off with some scrubbing.

It leaves no mark when I wear it on other fingers.
Then ring doesn't seem to have any substance or coloring on its inside.
Is it possible that this isn't on the outside but some blood-related issue under the skin?
Theories?

posted by signal to Health & Fitness (6 answers total)

The other fingers are thinner. Would the ring be in contact with the skin as much?

Are you sure it's aluminum? Copper is known to do this.
posted by dobbs at 11:43 AM on March 30

Response by poster: Then ring is a bit loose on all my fingers, including the one it marks.
My wife got it for me in Venice, she was told it's recycled aluminium. It has a silvery yellowish color.
posted by signal at 11:59 AM on March 30

It’s probably aluminum bronze:

Aluminium bronzes are most valued for their higher strength and corrosion resistance as compared to other bronze alloys. These alloys are tarnish-resistant and show low rates of corrosion in atmospheric conditions, low oxidation rates at high temperatures, and low reactivity with sulfurous compounds and other exhaust products of combustion. They are also resistant to corrosion in sea water. Aluminium bronzes' resistance to corrosion results from the aluminium in the alloys, which reacts with atmospheric oxygen to form a thin, tough surface layer of alumina (aluminium oxide) which acts as a barrier to corrosion of the copper-rich alloy. The addition of tin can improve corrosion resistance.[1]

Another notable property of aluminium bronzes are their biostatic effects. The copper component of the alloy prevents colonization by marine organisms including algae, lichens, barnacles, and mussels, and therefore can be preferable to stainless steel or other non-cupric alloys in applications where such colonization would be unwanted.

Aluminium bronzes tend to have a golden color.

posted by jamjam at 12:15 PM on March 30 [2 favorites]

Copper jewelry is the usually the cause of blue or green marks, as noted above. You aren’t getting a uniform reaction because either the PH, or more likely moisture is different in that particular spot.
posted by zenon at 5:22 PM on March 30

Supporting jamjam's theory that the ring is an alloy including copper: aluminium oxide (the substance that you'd see when pure aluminium oxidises) is white.
posted by Zumbador at 10:59 PM on March 30

Response by poster: Thanks all!
posted by signal at 12:37 PM on March 31