It was on all the wood laminate 'Jablo' props, to provide some protection against rain or icing. The blades themselves had a thin rubber membrane coating, for similar protection. To be honest, they can't be noticed unless a couple of feet away, and then you'd need to look closely. They were normally painted in a similar finish, so either matt or semi-matt black, and sometimes showed slight weathering, where the brass showed through. But again, in anything below about 1/24th scale, this wouldn't be seen, and in fact would look 'wrong', especially if weathered, possibly making a 'Jablo' prop appear to be a metal prop.
Far as I remember, the MkXIV used a 'Jablo', but of course both types could be fitted, depending on series production and in-service changes.