Black ring around wall penetration?

Can anyone help out with what this is? There is a black ring on the wall where the sink waste line penetrates the wall. Odd place for water damage.



Looks like previous brazing. Can’t be sure.

I’d just note the corroded p-trap and the absence of shut-off valves.

I got those, thanks Joe

It is from smoke and dust air going into the hole leaves some residue behind.

Why isn’t it on the painted surfaces?

Sure looks like fresh paint to me …

Must be one heck of a draft to stain the hole black. No lint or dust noted.

I vote burn marks.

The edges of the paper are charred.

I agree with Joe.

Torched to solder or braze fitting.