A California duster is similar to the push type dust mop that is inpregnated with an oil that grabs dust particles, BUT the California duster is a hand held string type duster and it is inpregnated with paraffin wax particles that grab the dust but don't leave a residue.
They acually seem to work better the dirtier they get, just shake off the loose dust and lightly dust away. Don't wash the California duster with detergent or it will remove the paraffin.
Richard