For drawing chalkboard art -for drawing a chalkboard to be precise.
Quite a challenge.
Since there are factors of the look you cannot simulate by filtering.
First, you have a wooden board painted black, with certain imperfections and small bumps, scatters etc. Upon it is a random layer of chalk powder, in the shape of a trace by a sponge.
The latter without filtering alone is a way advanced task.
But let's just focus on a much simpler look alike for now.
Pack is composed from three flood fills.