For light hair types it may not be necessary to wet hair before chalking, these hair types take colours very easily and by wetting hair you increase the pigmentation take up and the colours will last longer even after several washes like hair dye.
For darker hair types it is essential to wet hair using mists of water from a spray bottle, this helps the hair to take on the pigmentation by doubling the intake onto the hair but even so not in the way these are taken up on blonde or lighter hair types. For red hair types it may not be essential to wet hair, it would be a matter of preference and trialling what suits your hair style better.
For really fun and funky chalking why not use two colours on the same hair strands, this creates imaginative and individual hair shade which will stand out, we call it Tie-Dyed!
To remove colours from chalked hair it is a good idea to brush the hair with a soft brush before showering, to remove as much pigment as possible before using shampoo. Use clarifying shampoo to remove colours from chalked hair, remember that blonde hair types which used water would need several washes to remove the pigmentation. It is essential to use a deep conditioner on hair that has been chalked, this will replenish hair moisture recovery from the chalking process.