That black bit on the rudder leading edge is paint, Doves Devon s were fitted with liquid anti iceing via porous strips on the leading edges of wings, horizontal and vertical stabilizers supplied by a 6 gallons tank aft of the main baggage hold and windscreen anti iceing via a hand pump fed from a 1 gallon tank forward of the nose bay hatch, however they are all removed from most of the type with only one exception which I am aware of.