Brass is an alloy of copper and zinc, with copper always making up the majority. The exact percentages shift depending on the intended use, but most common brasses fall in the range of roughly 55 to 95 percent copper and 5 to 45 percent zinc by weight. Many brasses also contain small amounts of other elements like lead, tin, or arsenic, each added to fine-tune a specific property. The variety of possible ratios is what gives brass its remarkable range, from the reddish tones of low-zinc “red brass” to the bright gold color of high-zinc “yellow brass” and everything in between.
The Core Two Ingredients
Every brass starts with the same two metals. Copper forms the base, and zinc is dissolved into it to create a solid solution. When the zinc content stays below about 35 percent by weight, zinc atoms substitute randomly into the copper crystal structure without forming a separate phase. This single-phase region is known as alpha brass, and it is the most ductile and workable family of brasses. Push the zinc percentage above that threshold and a second, harder crystal phase begins to appear, producing what metallurgists call alpha-beta or duplex brass. Go higher still, past roughly 45 percent zinc, and you enter territory that is brittle and rarely useful for engineering purposes.
The distinction matters because the two-phase brasses behave very differently from single-phase ones. Alpha brasses can be cold-worked easily, meaning you can hammer, roll, or draw them into thin sheets and wire without cracking. The duplex brasses are better suited to hot working, like forging and extrusion, because the second phase makes the metal stiffer at room temperature but more cooperative at elevated temperatures. Most brass products you encounter in daily life are engineered to sit on one side or the other of that phase boundary, and the zinc percentage is the lever that determines which side.
How Color Changes with Zinc Content
One of the easiest ways to roughly judge a brass’s composition is by looking at it. Alpha brasses containing up to about 20 percent zinc appear distinctly reddish, sometimes close to a coppery rose-gold. Once the zinc content climbs above 20 percent, the alloy shifts to the familiar warm yellow most people associate with the word “brass.”1Journal of Minerals and Materials Characterization and Engineering. Evaluation of Mechanical and Microstructural Properties of α-Brass Alloy Produced from Scrap Copper and Zinc Metal through Sand Casting Process At the higher end, around 33 to 37 percent zinc, the color becomes a brighter, almost lemony gold. This color gradient is not just decorative trivia; it has practical consequences. Jewelers and architects often specify a brass grade partly by the color it will produce, and the yellow hues of higher-zinc brasses are a big part of why brass is chosen for decorative hardware, instruments, and fittings in the first place.
Common Brass Compositions and Their Names
The brass family includes dozens of standardized alloys, each identified by a numbering system (such as the Unified Numbering System used in North America). A few are worth knowing because they account for the vast majority of brass you are likely to encounter.
- Gilding metal (C21000): About 95% copper, 5% zinc. Used for jewelry, coins, and decorative items where a warm, coppery look is wanted. Barely yellow, almost indistinguishable from copper at a glance.
- Red brass (C23000): Roughly 85% copper, 15% zinc. Common in plumbing fittings and decorative trim. Has a noticeable pinkish-gold tone.
- Cartridge brass (C26000): Around 70% copper, 30% zinc. One of the most widely used brasses in the world, named for its original role in ammunition casings. Excellent for deep drawing and forming. Solidly yellow in color.
- Yellow brass (C27000): Approximately 65% copper, 35% zinc. Used for a wide range of stampings, hardware, and decorative items. Right at the edge of the alpha-phase boundary, giving it a good balance of strength and workability.
- Muntz metal (C28000): About 60% copper, 40% zinc. A duplex brass, harder and stronger, traditionally used for ship sheathing and large industrial fasteners. Must be hot-worked rather than cold-formed.
These compositions are nominal. Real production alloys vary by a percentage point or two depending on the supplier and the particular standard being followed. The names have stuck around for historical reasons and remain useful shorthand, but the critical information is always the copper-to-zinc ratio.
What Else Goes In Besides Copper and Zinc
Many commercial brasses are not strictly two-element alloys. Small additions of other metals, usually ranging from a fraction of a percent to a few percent, tailor the brass for specific jobs. The most historically significant additive is lead.
Conventional free-machining brasses contain roughly 3 percent lead by weight.2ScienceDirect (Elsevier). Comparative study on the machinability of lead-free brass Lead does not dissolve into the copper-zinc matrix. Instead, it sits as tiny globules scattered throughout the metal. When a cutting tool hits these globules during machining, the lead deforms into thin flakes that act as crack-starting points in the chip being removed. This breaks the chip into small, manageable pieces rather than letting it form long, stringy ribbons that tangle around the tooling. The result is lower cutting forces, less friction, cooler tool temperatures, and a better surface finish on the finished part.3The International Journal of Advanced Manufacturing Technology. On the function of lead (Pb) in machining brass alloys For decades, leaded brass was the default choice for any part that needed to be turned on a lathe or drilled precisely, which is why so many plumbing valves, faucet bodies, and lock components were made from it.
Tin is another common additive. Naval brass, widely used in marine hardware, typically contains about 60 percent copper, 39 percent zinc, and 1 percent tin.4ScienceDirect (Elsevier). Corrosion performance of naval brass in a simulated ocean water environment under different aqueous conditions The tin improves resistance to corrosion in seawater. Some naval brass grades also include a few percent of lead for machinability, creating a four-element alloy.
Arsenic appears in very small amounts, often less than 0.1 percent, in certain brasses designed for plumbing and heat-exchanger tubes. Its role is to inhibit a specific corrosion problem called dezincification, where zinc is selectively leached out of the alloy and leaves behind a weak, porous copper skeleton. Even a trace of arsenic dramatically slows this process.5Corrosion Science. Direct electrochemical measurement of dezincification including the effect of alloyed arsenic
Other additives you may see in specialty brasses include aluminum (for strength and corrosion resistance), manganese (for wear resistance), silicon (for casting fluidity and strength), and nickel (which begins to blur the line between brass and a different family of alloys called nickel silvers). Each of these is used in small quantities, rarely more than a few percent, and each solves a specific engineering problem.
The Shift Away from Leaded Brass
Lead makes brass easier to machine, but it also makes brass dangerous for contact with drinking water. Lead can leach from brass fittings into the water flowing through them, and there is no safe level of lead exposure from a health standpoint. Regulations in the United States, the European Union, and elsewhere have progressively tightened the allowable lead content in brass used for plumbing and water-contact applications. In the U.S., the Reduction of Lead in Drinking Water Act limits the weighted average lead content of wetted surfaces to 0.25 percent, a far cry from the 3 percent that was standard for decades.
This has driven the development of lead-free or low-lead brass alloys that use alternative elements, primarily bismuth and silicon, to recover some of the machinability that lead provided. Bismuth behaves somewhat like lead in that it forms discrete particles in the brass matrix, but it is far less toxic. Silicon-containing brasses take a different approach, relying on changes to the alloy’s microstructure to improve chip breaking during machining. Neither alternative fully replicates lead’s performance, and machinists working with lead-free brass often report higher tool wear and less predictable chip control, but the gap has narrowed considerably as alloy design has improved.
If you are buying brass fittings for a plumbing project, check whether the product is rated for potable water contact. Many hardware stores still carry leaded brass for non-water applications like gas lines and decorative hardware, so the distinction matters.
How Zinc Content Shapes Physical Properties
Beyond color, the zinc percentage changes almost every measurable property of the alloy. Strength generally increases as you add more zinc, up to about 45 percent, because zinc atoms distort the copper crystal lattice and make it harder for the metal to deform. Ductility follows a more complicated curve. It increases at first, peaking somewhere around 30 percent zinc, then drops off as the harder beta phase begins to appear. This peak in ductility at 30 percent zinc is exactly why cartridge brass (70-30) became so popular for applications requiring deep drawing and forming.
Electrical and thermal conductivity both decline steadily as more zinc is added. In the alpha-phase region, the random substitution of zinc atoms into the copper lattice increases scattering of conduction electrons, shortening their mean free path and reducing how well the alloy conducts electricity and heat.6PubMed Central. First-Principles Study on the Electrical and Thermal Conductivities of Cu–Zn Binary Alloys Pure copper is one of the best electrical conductors available, but a 30 percent zinc brass conducts only about a quarter as well. This is why copper, not brass, is used for electrical wiring. Brass does find a niche in electrical connectors, where the combination of decent conductivity, spring resilience, and corrosion resistance matters more than raw conducting ability.
Cold working, the process of mechanically deforming the metal at room temperature, also dramatically affects strength and ductility. A piece of annealed (softened) brass has maximum ductility and the widest gap between its yield strength and its ultimate tensile strength, meaning it can absorb a lot of deformation before breaking. Cold working boosts the strength while narrowing that gap, making the brass harder but more brittle.7Encyclopedia of Materials: Science and Technology. Electrical and Electronic Connectors: Materials and Technology – Section: 5.1 Copper-based Spring Materials Spring contacts in electrical connectors, for example, are made from heavily cold-worked brass to achieve the springiness needed to maintain a reliable connection.
Brass as an Antimicrobial Surface
A property that has attracted renewed attention in the past two decades is brass’s ability to kill bacteria, viruses, and fungi on contact. This antimicrobial action comes from the copper component. Copper ions released from the brass surface damage microbial membranes, interfere with proteins, and cause DNA damage through oxidative stress.8PubMed Central. Brass Alloys: Copper-Bottomed Solutions against Hospital-Acquired Infections? Direct contact with the metal surface also contributes: pathogens that land on brass are killed far more quickly than those on stainless steel or plastic, which merely provide a surface for microbes to sit on.
The zinc percentage matters here too. Higher-copper brasses tend to be more potent antimicrobials because there is simply more copper available to release ions. Alloys below about 60 percent copper show reduced killing rates. This has implications for public health applications. Hospitals experimenting with copper-alloy touch surfaces, like door handles, bed rails, and faucet levers, have generally favored alloys on the copper-rich end of the spectrum. Brass is cheaper than pure copper and still mechanically practical for hardware, making it a compelling middle ground between cost and antimicrobial performance.
How Brass Corrodes and Why It Matters
Brass’s corrosion story is more interesting than “it turns green.” The green patina that forms on outdoor brass is a surface layer of copper carbonates and oxides, similar to what happens on a copper roof, and it actually protects the metal underneath. The more troublesome forms of corrosion are subtler.
Dezincification, mentioned earlier, is the selective loss of zinc from the alloy. In aggressive water conditions, particularly warm, slightly acidic water with chloride ions, zinc dissolves away preferentially, leaving behind a porous, spongy mass of copper that looks intact but has lost most of its mechanical strength. This is a real-world problem in plumbing systems and has caused failures in valves and pipe fittings. The fix is either to use a low-zinc brass (alloys below about 15 percent zinc are effectively immune) or to use an alloy containing a small amount of arsenic, which inhibits dezincification even in aggressive environments.5Corrosion Science. Direct electrochemical measurement of dezincification including the effect of alloyed arsenic
Stress corrosion cracking is another failure mode that has been known for well over a century. Brass under sustained mechanical stress in the presence of ammonia or ammoniacal compounds can develop cracks that propagate along the grain boundaries of the metal. The combination of tensile stress and a chemically aggressive environment causes cracking that would not occur from either factor alone. Research has shown that ammonia vapor is more damaging than liquid ammonia solutions, and the presence of dissolved copper ions in the environment accelerates the attack.9Matéria-Reserva. Observations of Corrosion Product Formation and Stress Corrosion Cracking on Brass Samples Exposed to Ammonia Environments This is why brass should not be used in environments where ammonia exposure is expected, such as certain chemical plants and refrigeration systems that use ammonia as a coolant. Old ammunition casings made from cartridge brass were notoriously vulnerable to this problem during tropical storage, where decomposing organic matter produced trace amounts of ammonia in the air, hence the historical name “season cracking.”
Recycling and the Composition Question
Brass has one of the highest recycling rates of any engineering metal. Because both copper and zinc are valuable, scrap brass is routinely remelted and recast into new products. The challenge is that every piece of scrap carries its own composition, and mixing different grades together produces a melt with an unpredictable zinc percentage. Foundries and recyclers deal with this by analyzing the melt and adjusting the chemistry, adding zinc if the content is low or diluting with copper if the zinc is too high.
At high remelting temperatures, zinc evaporates far more readily than copper because of its lower boiling point. Research on zinc evaporation from brass scrap has shown that at temperatures between about 1,080 and 1,240 degrees Celsius, anywhere from 82 to 99 percent of the zinc can be driven off.10PubMed Central. Zinc Evaporation from Brass Scraps in the Atmosphere of Inert Gas This is both a problem and a tool: it means recyclers must carefully control melt temperature and atmosphere to avoid losing zinc unintentionally, but it also means zinc can be deliberately removed from copper-zinc scrap when the goal is to recover relatively pure copper. Inert gas atmospheres and precise temperature control help manage the process.
For the end user, the recyclability of brass is a genuine environmental advantage. Unlike many engineering materials where recycling degrades performance, remelted brass can be brought back to the same compositional specifications as virgin alloy. The copper-zinc ratio is simply re-established to whatever the target grade requires, and the resulting metal is functionally identical to brass made from freshly mined ores.
Why the Same Alloy Ends Up Everywhere
The reason brass is found in such a wildly diverse range of applications, from saxophone bells to plumbing valves to ammunition casings to zipper teeth, comes down to how tunable it is. Adjusting the zinc content shifts color, strength, ductility, and cost along a smooth continuum. Adding a percent or two of a third element opens up whole new capability sets like free machinability, seawater resistance, or dezincification immunity. And the resulting alloy is still easy to cast, forge, stamp, or machine, still resistant to corrosion in everyday environments, and still looks attractive enough to leave exposed in architectural and decorative applications.
Few alloy families offer that combination of range and versatility. Steels are stronger but rust without coatings. Aluminum alloys are lighter but softer and less corrosion-resistant in many water environments. Pure copper is a better conductor but too soft for most structural applications. Brass occupies a middle ground that has kept it relevant for thousands of years, and the percentages of copper and zinc in any given piece are the key to understanding what that particular brass was designed to do.