The hall 1/2 bath under the sink the water shutoffs have corroded green. The braded water line have corroded and the hidgenes have corroded The cabinet base is OK and dry. The only thing I can think of is battery acid corrosion. The house is only 3 years old. No signs anywhere else in house or garage.
Could be a dialectic union (copper and whatever). Could be condensation. Could be chemicals stored under the sink.
If the wood was fine, then my gess would be something other than condensation.
Appears to be patina caused from cleaning products or anything with chlorine, other harsh or caustic chemicals stored can also do this.
Clorox and Comet products, emitting fumes, come to mind…
I see this a lot in copper systems where pool chemicals are stored in proximity to equipment. The insides of panel equipment are rusted and look like hell and I had a dead front basically fall off in my hands as I was removing screws…work safe out there
Thanks Barry that is what I thought it was
Can this also happen in a ceramic bathroom?