Correction Bit Micky Mouse Normal Shank

The shanks are made of stainless steel and will rust less.
The mouthpiece is actually made to rust.

The mouthpiece develops surface rust through contact with (air) moisture that tastes sweet and naturally stimulates salivation, which improves acceptance of the bit. This rusting process (oxidation) changes the color of the bits to brownish gray.

A beginning of this desirable oxidation process may already be visible when purchasing a new bit.