Brass alloys explained

At a glance

Composition is as printed on stockholder datasheets (A and B are two UK stockholders; CW501L is from a stockholder web page), which cite the EN product standards; zinc is the balance apart from lead and small additions. They are not the standards themselves: confirm against the current edition and the mill certificate. No colour is given on any of these datasheets, and none is claimed here.

Why "brass" is not enough

Brass is any alloy of copper and zinc. The word covers a wide range, from about 90% copper at one end to a little over 55% at the other, with or without lead. That balance changes how the metal forms, how it machines and how it welds. It also changes how it looks, in ways no datasheet puts a number on.

Alloys have an EN number such as CW508L. UK stockholder datasheets still print the older CZ number beside it (CZ108), and a chemical symbol (CuZn37) that gives the nominal zinc. In the stockholder glossary we read, CZ108 is the 63/37 brass that is also called common brass. A specification that says only "brass" leaves the choice to whoever buys the metal, and two buyers will make different choices.

The drawing places eight alloys by copper content. The dashed line is where the structure of the metal changes, at about 36 to 37% zinc. To the left are the alpha brasses, which cold form well. To the right are the alpha-beta (duplex) brasses, which the glossary says are better for hot working and worse for cold working.

Which alloy for which job

Match the alloy to how the part is made. The datasheets point the same way each time: low-lead alpha brasses for forming, leaded duplex brasses for machining and hot pressing.

Starting points drawn from the "typical use" lines on the datasheets, not an approved list. Your partner workshop confirms what it buys and works.

Two cautions follow from the table. Do not ask a free-cutting bar to behave like sheet. The glossary says CW614N has one of the fastest rates of metal removal but that its ductility is compromised, and it notes that the beta phase harms cold formability. And do not assume one alloy will serve a whole scheme: sheet, turned parts and extrusions often come from different alloys, which matters when they must match (see colour below).

Lead, and zinc loss in water

Lead. The free-cutting and stamping brasses carry roughly 1.5 to 3.5% lead on the datasheets. The glossary says lead usually improves machinability. The common sheet brasses carry 0.10% or less. If a project needs lead-free or low-lead metal, because of a client policy or because the part touches skin or water, say so in the specification and let the alloy name follow. We give no legal view on lead limits here.

Zinc loss. The glossary defines dezincification as the selective corrosion of the beta phase in duplex brass, leaving a copper-rich residue. Dezincification-resistant (DZR) brass, CW602N, adds arsenic and a heat treatment to prevent it in soft, acidic domestic water supplies. For dry decorative metalwork this is rarely the issue. It matters for parts that carry or stay in contact with water. Our sheet on which metal for which environment shows how brass rates across six exposures.

Cracking. The glossary adds that alpha brasses are susceptible to stress corrosion in atmospheres containing ammonia, and that a stress-relieving heat treatment helps. It is worth knowing when a formed part will sit in a room cleaned with ammonia-based products.

Colour, finish and welding: what the datasheets leave out

• Colour. None of the datasheets gives a colour for the common alloys. The colour words we found are few. A 90/10 gilding brass is called golden. CW624N has an aesthetically pleasing finish on one datasheet and a yellow lustre on another. A manganese brass is called a warm "chocolate". Nickel silver is called silvery white. The general idea, that more copper looks more golden and more zinc looks paler, appears in a public reference with no source, so treat it as a guide only. Specify colour by a physical sample cut from the same alloy and finished the same way.
• The word "bronze". Bronze is a copper and tin alloy. The glossary calls "architectural bronze" a loose term for several brasses coloured like bronze, so it is not an alloy name to specify.
• Finishing. On the coating house datasheet we read, brass needs a nickel and chrome plating layer before a PVD finish. A clear lacquer needs a clean, freshly buffed surface. Both are covered in lacquered or unlacquered brass and copper and PVD coatings explained.
• Welding. The datasheets do not agree in emphasis. The CW508L sheet datasheet lists excellent weldability, while the CW617N and CW602N datasheets class gas-shielded arc welding as not recommended. Our own journal says welding brass is demanding because zinc boils off. Ask the partner which alloy they weld and how they finish the weld; see can you weld brass.
• Ageing. Every brass keeps changing at the surface unless it is sealed. How fast, and how evenly, depends on the alloy, the room and the hands that touch it. See patination.

What to put in a specification

• The alloy by EN number and symbol, for example CW508L (CuZn37), never "brass" alone.
• The product standard for the form, as the datasheets cite it: EN 1652 for sheet and strip, EN 12164 for free-machining bar, EN 12167 for profiles, EN 12449 for tube. Edition to be confirmed.
• The temper, where it matters for forming or springiness; the tube datasheet offers half hard. Agree it with the partner.
• A lead statement, if the part is handled or in contact with water.
• Dezincification resistance, for parts that stay wet.
• A reference sample in the same alloy and finish, with every visible part of one run cut from the same batch where possible, and no change of alloy without written approval.
• A material certificate from the stockholder or mill, kept with the project file.

Brass sheet to [EN 1652, edition to be confirmed], alloy [CW508L (CuZn37)], temper [half hard], [__] mm thick. Lead not above [0.10]% per the material certificate. Finish [name, code] as approved sample [ref. __]. One visible run from one batch where possible. No change of alloy without written approval.

Brass bar to [EN 12164, edition to be confirmed], alloy [CW614N (CuZn39Pb3)], with a material certificate for each batch. Finished to match reference sample [ref. __]. Where the part must match adjacent sheet in [CW508L], the finished parts are checked side by side in the project lighting before production.

Component: [alloy named by the partner, for example CW602N (CuZn36Pb2As), dezincification resistant]. Evidence of resistance [test report or certificate ref. __]. Lead content [__]% and the compliance route for [drinking water / skin contact / not applicable] to be stated in writing by the partner before the sample is approved.

Match to the existing [element, location] within [tolerance agreed with the partner], on physical samples in the same alloy [name] and finish [name], viewed in the project lighting. The partner states the alloy proposed and, if known, the alloy of the existing metal.

Standards and sources

• UK copper-alloy stockholder datasheets: CW508L, CW505L, CW606N, CW614N and CW624N (each updated 5 December 2024); CW602N and CW617N from a second stockholder (2023).
• A stockholder's Copper Glossary of Terms and a gilding-brass web page: alpha, duplex, free-machining and DZR brass, dezincification, season cracking, nickel silver, architectural bronze; CW501L.
• A coating manufacturer's decorative PVD datasheet: brass needs nickel and chrome plating before PVD; read 5 November 2026.
• BS EN 1652, BS EN 12164, BS EN 12167, BS EN 12449: named on the datasheets; text not read. Confirm the current edition.
• Make Bespoke Studio, TL-MET-02: which metal for which environment: brass among eight metals and six environments.

Questions we are asked

What is the difference between CW508L and CW614N?

CW508L is the common sheet brass: about 63% copper, very little lead, good hot and cold forming and bending. CW614N is a free-cutting bar brass: about 58% copper and 2.5 to 3.5% lead, with the highest machinability of any copper alloy but poor ductility. One is for forming, the other for turning and milling.

Which brass is used for sheet and folded panels?

On the stockholder datasheets the common sheet brass is CW508L, with CW505L (about 70% copper) for deep drawing and spinning. Your partner workshop confirms which alloy it buys, and that is the alloy to name in the specification.

Is brass the same as bronze?

No. Brass is copper and zinc, bronze is copper and tin. The stockholder glossary calls "architectural bronze" a loose term for brasses whose colour mimics bronze, so name the alloy and show a sample rather than writing "bronze".

What does DZR mean, and when do I need it?

DZR is dezincification-resistant brass, such as CW602N. It is made to resist zinc loss in soft, acidic water, so it belongs in parts that stay wet, such as water fittings. For dry decorative metalwork the common brasses are normally used; ask the partner if a part will be wet.

Why do two brass samples look different?

The alloy, the finish and the age of the surface all change the colour, and no datasheet gives a colour. Two nominally identical brasses can differ by copper content, by polish or grain, by lacquer and by how long they have been handled. Match by physical sample, in the same alloy and finish.

Does brass contain lead?

Some does. The free-cutting and stamping brasses carry about 1.5 to 3.5% lead on the datasheets, and the common sheet brasses 0.10% or less. If lead matters to the project, say so in the specification and have the partner name an alloy and show the certificate.

Is nickel silver a type of brass?

No. Nickel silver is a copper, nickel and zinc alloy, with no silver in it. The glossary describes it as silvery white. It is an option when the brief wants a pale, cool metal that is not stainless steel.