Austin alloys on UK spec Golf GTI’s were diamond cut, so the face of the spokes would have originally had a diamond cut finish, and the areas between the spokes would’ve been painted / powder coated black. There wasn’t a painted powder coated option from the factory for Austin’s.
The diamond cut finish isn’t particularly durable, especially during winter months. Any damage to the lacquered surface and water can ‘creep’ under the lacquer and spread over the diamond cut areas. This is probably what happened to the wheels on your car, so the previous owner had them refurbished in a more durable painted / powder coated finish.
