Black stripes on sheetrock at each stud

Hi all,
I Was emailed a pic of Sheetrock in a bedroom that had black stripes at each tape seam on the walls and ceiling. What do you think it is ?


At “each stud” or at “each tape seam”??? Makes a difference.

Most likely “ghosting”.

Sorry, each stud.

Like this? Soot, from candles.

Yes like that. I can’t post pics from my iPhone. I just thought it was odd being at each stud.

Thermal Bridging

I think Troy has the literal definition. “ghosting” is the common name.

Are there/were there candles in this bathroom? Perhaps a wood fueled heater nearby? Heavy smokers?

Yep, I agree with Troy – thermal bridging causing condensation to trap dust.