Why are blue finishes more durable tha CC?

[Craig Budgeon]

Another way of expressing it is that rusting bluing is achieved by applying multiple layers of rust which is carded off until the desired depth of blue is achieved. Case color is a pleasant side affect from the necessary process of casehardening and has very little durability unless the parts are externally lacquered. Nitre blue is another heat related process which has little durability and little depth but is inexpensive for manufacturers