Air carrier Flight Attendant reported a thick layer throughout the cabin in what appeared to be like chimney soot during the boarding process. Captain reported this to Maintenance.

Narrative

At the end of boarding the previous flight to this one I had noticed my gloves were black and at first I just thought it was dirt from the bins because the bins were dirty looking. The other FA said the same thing and said look at how dirty my hands are and I said it's from the bins my gloves are filthy too. Then boarding the flight to ZZZ ; (the very next flight) I noticed the whole bathroom door was covered in a thick layer or what looked like soot from a chimney. And I told the captain and then he noticed the flight deck windows were covered with a thick layer and other pilots wiped down the windows and I said look it's even on the ceiling surrounding the controls and you could write your name on it with you finger! We were sure if the plane had maybe been used in the hangar and got dirty or what but we had a flight deck jump seater as well during that flight and he noticed in the air vent during flight it was black like soot when he checked it. When we landed we noticed more above the bins and not sure if that was there prior to departure or not but it was obvious it wasn't just dirt from being at the hangar and the Captain called it in.