Brass & Bronze Etchants

Complete guide to selecting and applying etchants for brass and bronze alloys. Covers ammonium hydroxide, nitric acid, and ferric chloride reagents with compositions, conditions, and troubleshooting for copper-zinc and copper-tin alloys.

Brass Prep Guide Etchant Selector Tool

Manganese-Aluminum Bronze Alloy Microstructure, 400X DIC

Alloy Classification & Preparation

Understanding the alloy system helps select the right etchant. Brass alloys are copper-zinc, while bronze alloys are copper-tin.

Common Brass Alloys (UNS)

Copper-zinc alloys with varying zinc content for different properties.

View alloy breakdown

C21000 — Gilding Metal (95% Cu, 5% Zn) – Coins, jewelry
C22000 — Commercial Bronze (90% Cu, 10% Zn) – Hardware, conduit
C23000 — Red Brass (85% Cu, 15% Zn) – Plumbing, condenser tubes
C26000 — Cartridge Brass (70% Cu, 30% Zn) – Ammunition, springs
C28000 — Muntz Metal (60% Cu, 40% Zn) – Architectural trim
C36000 — Free-Cutting Brass (61.5% Cu, 35.5% Zn, 3% Pb) – Screw machine products
C46400 — Naval Brass (60% Cu, 39.25% Zn, 0.75% Sn) – Marine hardware

Common Bronze Alloys (UNS)

Copper-tin alloys and related compositions for specialized applications.

View alloy breakdown

C51000 — Phosphor Bronze A (95% Cu, 5% Sn, 0.2% P) – Springs, electrical contacts
C52400 — Phosphor Bronze D (90% Cu, 10% Sn) – Heavy springs, bridge bearings
C54400 — Free-Cutting Phosphor Bronze – Bearings, bushings, gears
C61400 — Aluminum Bronze D (91% Cu, 7% Al) – Pump parts, marine hardware
C63000 — Nickel Aluminum Bronze (82% Cu, 10% Al, 5% Ni) – Valve seats, marine
C65500 — High Silicon Bronze A (97% Cu, 3% Si) – Hydraulic pressure lines
C86300 — Manganese Bronze (63% Cu, 25% Zn, 6% Al) – Heavy-duty gears

Preparation Tips

Brass and bronze are soft, ductile materials prone to mechanical deformation.

View key considerations

Use low-nap polishing cloths to minimize surface relief between phases
Avoid excessive pressure during grinding to prevent smearing of the soft copper matrix
Vibratory polishing with colloidal silica produces excellent final results
Alpha brass is particularly prone to twinning which is readily revealed by etching
Multi-phase alloys require careful etchant selection to differentiate phases
Clean thoroughly between preparation steps to prevent cross-contamination

Recommended Etchants

Selecting the right etchant is crucial for revealing brass and bronze microstructures. For a comprehensive searchable list, visit the Etchant Database.

Etchant	Composition	Conditions	Applications
Ammonium Hydroxide (dilute)	Ammonium hydroxide: dilute solution	Immersion Attack polishing	General purpose attack polishing etchant for copper and copper alloys ASTM 30 is also a good etchant for copper and copper alloys
Copper No. 1	Nitric acid: 125 ml Distilled water: 125 ml	Immersion or swabbing 1 second to several minutes	Common etchant for copper and copper alloys such as brass and bronze Reveals grain boundaries and twinning
Copper No. 2	Distilled water: 200 ml Ferric chloride: 10 g Hydrochloric acid: 50 ml	Immersion or swabbing Several seconds to minutes	Brasses, bronzes, and aluminum brass Excellent for revealing alpha phases in brass Differentiates alpha and beta phases in two-phase brasses

Troubleshooting

Common etching issues and how to resolve them.

Over-etching

Surface appears too dark or pitted. Reduce etching time significantly—brass and bronze etch quickly, especially with nitric acid. Start with 1–2 seconds and increase gradually.

Under-etching

Grain boundaries not clearly visible. Increase etching time incrementally or ensure the etchant solution is fresh and at proper concentration.

Uneven Etching

Ensure sample is completely clean and dry before etching. Residual polishing compounds can cause localized over- or under-etching.

Staining

Rinse immediately with water after etching and dry with compressed air or alcohol. Copper alloys are prone to tarnishing if left wet.

Poor Phase Contrast

For multi-phase alloys (alpha-beta brass, aluminum bronze), try ferric chloride-based etchants (Copper No. 2) for better phase differentiation.

Smearing Artifacts

If the etched surface shows directional artifacts, the sample may not have been polished adequately. Re-polish and re-etch with fresh solution.