On Mon, 11 Jan 2021 20:26:52 +0000, alan_m wrote:

Candles are the big problem if it coincides with a lack of dusting and
vacuum cleaning, or if there is a lot of cooking based on frying.

Didn't read the original question because of HoH -- but a deposition of black
dust on walls can be an unlucky combination of volatile plasticisers (from
paint, furniture, plastics, etc.), heating, and volatile organic compounds.

More (but not much) to be googled by "fogging", "black magic dust", and "black
dwellings phenomenon".


Thomas Prufer