Metal Alloys


The simplest bronze is copper mixed with small amounts of tin. Tin increases hardness, making bronze more resistant to wear than copper. Bronzes are usually harder, stronger, and more resistant to corrosion than brass, which is a copper and zinc alloy. The ones we tend to use are:

Phosphor bronze

contains a small amount of phosphorus, which further increases the hardness and wear resistance of the metal. In addition, it allows molten bronze to flow better, which enhances its casting quality. Phosphor bronze is available in wrought form in a wide range of bar, sheet and tube forms, which we can weld together. We use this for fabrication and castings. It has a reddish-gold colour which naturally patinates to a soft brown. In its hard state it is about as strong as mild steel.

Leaded bronze

Leaded bronze has lead, usually in small amounts, mixed in to act as a lubricant. Such bronze is often used to make parts that must endure a lot of sliding action. It was historically used in the manufacture of cannon – indeed one version is still called gunmetal – now more commonly for bearings and general castings. We use leaded gunmetal for general purpose castings. It polishes well to a rich gold colour. Left to its own devices it goes a greenish brown.

Silicon bronze

Silicon bronze has small amounts of silicon, which makes it grow stronger when it is worked, such as by rolling. It is also particularly resistant to corrosion. As well as being commonly used for investment casting, it is used to make fastenings such as woodscrews and gripfast nails.

Higher strength bronzes – for example aluminium bronze and manganese bronze – are available for applications where the strength is critical. Aluminum bronze is used for some tools and aircraft and automobile engine parts. Manganese bronze is actually a brass that contains manganese. It is often used to make ships propellers and shackles because it is strong and resists corrosion by sea water.

Both these alloys are somewhat yellow in appearance – similar to brass.

Brass and Copper

Brass is an alloy of copper and zinc - typically 30-40% zinc - with a characteristic yellow colour. It forms well, and plates and polishes well, but is not readily weldable. In a polished item we can nearly hide the weld, but we have never found a way to hide the join when brass is patinated. Where possible, then we use mechanical fixing if the piece is to be patinated.

Gilding Metal is version of brass with a much lower zinc content (10%), which forms well, welds well and patinates nicely. Looking much like bronze, it is only available in sheet form, so is often used for cladding

Copper is sometimes used in sheet form. Like brass it forms well and looks attractive in its own right. It patinates to a lovely rich red-brown.