The black dust may be due to deteriorating duct liner materials in your heater or air conditioner and in some cases your cold air returns.
Black dust on fan blades.
It may alternatively be due to soot produced from candles.
This same thing happens to the leading edges of your ceiling fan blades.
You don t want to lather it on but make sure it reaches every part of every blade.
Next you re going to make sure that each blade is dry.
Step 2 wipe the fan mount and housing with a damp cleaning cloth or microfiber cloth to remove dust working from the ceiling down toward the blades.
If the register is closed the air is forced along the ceiling and the next thing you know you ll start to see black buildup across your ceiling.
Over time a large volume of the circulating air hits and collects on the blades of the fan.
Soot deposition is most likely to occur on wall and ceiling surfaces in rooms where candles are burnt.
Additionally fan blades move rapidly through the air rubbing and brushing against air molecules and pushing them out of the way.
I suggest you use each paper towel until it gets dark and starts smearing dust or until you move on to the next fan blade whichever comes first.
Most of the dust particles that are floating in your house has some sort of electric charge which can often cause dust molecules to attract together hence the dust bunnies underneath your bed.
The air always has a great deal of dust in it larger particles that you can see and also microscopic ones.
Once they re all dry apply your paste car wax.
But they must understand that there is a lot of dust in the circulating air.