most w.i gates are painted with a lacquered based paint and would normally use thinner in the spray on process. using turpentine would be a big mistake in repainting these gates.
firstly,begin by removing any flaking paint by using a wirebrush,after that use an etching primer to coat these areas.
most of these gates have a black base coat.
Once the black base is complete,get the antique w.i paint finish (can be bought at any diy shops)and take a dab of paint on the brush and using a piece of cardboard or newspaper began releasing the paint on to it until it is almost dry.once this is done began brushing on to the gate itself in a uniform manner. keep doing tis until you see the antiquing effect that is the hallmark of a w.i gate.
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