Preserve with PaintIf a piece of iron is left outdoors it soon rusts because it combines with oxygen. A piece of unpainted wood will soon rot unless it has been specially treated (or unless it is an unusually resistant variety of wood, such as California redwood). In order to preserve certain materials outdoors, we must protect them by painting or varnishing. People often wonder why steel and iron fences, and bridges are first painted red-orange and then covered with black paint. The orange paint contains lead oxide, which gives it its color.This paint sticks to the iron surface and protects it from the oxygen in the air. The second coat of paint, which is black, will stick to the orange paint better than it will stick to the iron itself. The finished job is black just for the sake of appearance.