Clean Dry hair is best. Putting gunk on the hair only weights it down
and may cause it to stick to itself and reduce the effect. The best I
have ever produced was with a blue eyed blond (very fine hair-not
bleached). Her hair was about 40-50 cm long. EVERY strand stood out!
It was fantastic.
The atmospheric conditions play a very important part in the success or
failure of the demonstration. I am fortunate in having a good air
conditioner in my room that I can lower the humidity to 20% or so even if
it is foggy outside. If the outside air is reasonably dry, I can get
much lower. Make the room as DRY as possible.
I have borrowed a large rectangular glass tank (1+ cm thick sides) that I
use to insulate the student from the ground. I have also used a wooden
stool with good results. The Science Center in town uses a "Rubbermaid"
plastic step stool with their generator.