Brass is an excellent material for door knockers.

Brass is a nonferrous metal with good electrical and thermal properties. It also has excellent strength and corrosion resistance. Being an alloy it is available in many varieties. Not all brasses can make good brass door knockers though.

Brass is not a natural element, it is an alloy of copper (Cu) and zinc (Zn). Other elements such as lead, nickel and tin may be added to the mix to achieve certain properties. Depending on the final product to be made the mixture making up the brass can vary. Some brass parts need to be strong while some may need to be resistant to salt water and still others may simply need to look good. The recipe can be changed to accommodate each of theses requirements.

Sometimes the changes cannot be detected just by looking and other times differences are quite apparent. Some of the changes affect the color of the brass which can vary from silver to gold to red depending on the mixture.

A door knocker needs to be made from a bright yellow brass that casts and polishes well. It must also be machinable and engraveable.

The desired properties are achieved by keeping the copper content around 67%-72%, the zinc content around 24%-29% with 1%-3% each of tin and lead. As a general rule the higher the copper and lower the zinc contents, the softer and easier to machine the brass is.

The addition of a small amount of lead makes the brass easier to machine. Tin is added to increase strength and corrosion resistance. Tin will also help prevent the zinc from leaching out of the brass over time.

A quality finished product requires a quality “recipe” for the brass. There are many specifications written for brass that may apply to different industries. Standards are written by such organizations as ASTM, SAE, CDA and MILITARY to name a few.

The elements that make up the brass are mixed in a foundry. They are melted together at temperatures that vary around 1800F – 1950F. When molten the liquid mixture can be poured into a mold to form the product or poured into an ingot for storage for later use. Most product foundries purchase the brass already mixed in ingot form. The ingot is then remelted and poured into a mold to make a product.

After the brass is molded into a shape it is called a casting. The casting is then polished, finished and machined into the completed brass door knocker.