Vacant dwelling wire blackening

As if we all need one other thing to check at inspections, did one on a house that was vacant for 3 years, shadow bank inventory. 1930 home no drywall. Went inside, reeked of sewer gas as the traps had all dried up and the house was sealed up with no AC running for 3 years. Client was concerned about the wiring being knob and tube and no utilities on to tic test the attic wires so started pulling outlets and switches. The cooper wiring ends that were stripped to attach to terminals was all blacked like toxic drywall wiring. I surmised from the sewer gas fumes. When I scraped it with my flathead it just fell off and the copper sheen returned. Spoke to my electrician and he advised that he’s seen the same thing caused by sewer gas, and recommends all outlets/switches would need to be taken out, cleaned, and reattached. First time I had come across this particular issue, but just wanted to pass along to any others that run into a similar situation. Even though it exceeds the SOP, I woulda never thought to check the wiring for something like that.

Didn’t realize that sewer gas would cause this…makes sense though. Did you need a respirator for that one, since the traps are kind of hard to reseal without the water being on? Was there K&T in the home after all?

See the attached photo for various compounds that turn copper different colors.

Opened all the windows and doors while I did the outside and roof, after it aired out, it was tolerable. No knob and tube, just 1950-60 2-wire ungrounded.