Metal guttering should be well painted for protection. First test the pipework to see if it has been treated with bituminous paint. To do this apply a little white gloss to a small area of the gutter. If the gloss turns brown the coating is bituminous and you will have to apply an aluminium primer to prevent it ‘bleeding’ through the new paint. (Remember that the guttering may have been painted with bitumen on the inside only.) Paint the outside of the guttering with an undercoat and a top coat to complement the rest of your exterior decoration. It does not matter what colour you paint the inside of the gutter since it cannot be seen from the ground, so here is the ideal opportunity to use up any leftover gloss from other jobs.