The brilliance of the sweet iron bit lies in how it reacts when exposed to moisture. What happens you see, when for instance it is placed in your horses's mouth, is a surface layer of oxidisation will occur. This rust in turn will then tingle in the horse's mouth, and stimulate salivation.
Sweet iron is not only a lovely, warm metal which will heat up quickly in the mouth to body temperature, but it's taste also encourages salivation and bit acceptance.
It is completely safe for your horse, and all you need do in fact is quickly wipe the bit after use with a clean cloth to keep it in top condition.
Therefore, please do not be alarmed if your shiny blue Bomber bit goes rusty and blackens over time, this is completely normal and what we need to see happening.
If a used bit is going to be left unused for some time, particularly if left in a damp environment, we suggest cleaning and drying and placing a protective barrier over the metal (such as vaseline) to prevent it from becoming overly rusted. If you have found that it has formed an excessive layer of rust rather than having the normal "blackened" appearance, then simply soak in warm water and use a cloth or scouring pad to remove the excess rust and bring it back to its' best.
It can, rarely, become rough with age, and if this does occur, we suggest that you lightly sand it down with a very fine wet/dry sand paper to restore the smooth surface.
How a Bomber Sweet Iron Bit should look after prolonged use...