Out in the elements a protective coating is needed to prevent the brass from oxidizing or tarnishing. This is the process that happens when oxygen and atmospheric gasses comes into contact with the surface of the brass.

In normal use your brass door knocker should not require much attention.  It should just hang on your door looking good for many many years to come.
Occasionally a cleaning may be necessary.
Care should be taken if you attempt to clean your brass door knocker. Like the rest of your brass door hardware it will scratch [...]

A brass door knocker is not just another accessory on your door. It is part of the image that your house conveys.
When a person approaches the entrance to your home what impression would you like them to have. That of a building or that of a home. It is the accessories that makes the difference. [...]

A door knocker needs to be made from a bright yellow brass that casts and polishes well. Not all brasses are alike.

When engraving a name on engraved door knockers there always seems to be a question of what form to use.

A door knocker installation that uses the through the door mounting method requires drilling holes through the door. Care must be taken when drilling these holes.

If you are preparing for a door knocker replacement and it is a through the door installation the bolt center dimension has added meaning.

The phrase Bolt Center references the geometric center of the diameter of the hole being drilled.

Surface mount uses screws that pass through the door knocker and into the door.

Brass has many benefits when it comes to door knockers.