Ionic air purifiers. They charge or magnetize the particles and then they cling to everything. Remove a picture from the wall - is the ghosting around the outside? Remove a metal decorative piece - if the particles are magnetized the ghosting will be the opposite - it will be in the same design as the item.
Are you sure it is not mold? That could be a health risk. If you heating with an oil fired furnace it might be cracked and allowing exhaust in your home. You might need to have this checked out proffessionally since the by product of this exhaust is carbon monoxide.
burning oil
It usually means too much fuel or not enough spark.
because the soot from the candle rises and sticks to the ceiling which is how they get dirty
To stop the black residue from a baseboard heater, the wall around and near the heater should be cleaned as there are dust particles attached to the wall. This is called ghosting which fine particles of soot attach to the wall that is cooler than the temperature.
A black ceiling fan is likely to show the same amount of dust, unless the dust is dark in color. For instance, it could be mold spores or soot particles from candles. In this case a black fan will be less likely to show the particles.
soot
Soot is often produced when burning wood.
Soot will accumulate over time and may form more quickly if the gas contains impurities.
Soot is a noun. It is the black residue left behind by burning some substances.
The formation of black soot indicates that the combustion is not receiving enough oxygen and is incomplete. Black soot is made from mainly carbon.
I think you might be talking about soot. Soot is the leftover stuff from when wood or other materials are burnt.