Copper Alloy Etchants

Complete guide to selecting and applying etchants for copper alloys. Covers ammonium hydroxide, nitric acid, ferric chloride, and Weck’s reagents for pure copper, brass, bronze, and specialty copper alloys.

Copper Alloy Prep Guide Etchant Catalog

Tough Pitch Copper Microstructure, etched, 100X

Alloy Classification & Preparation

Copper alloys are designated by UNS numbers spanning wrought (C1xxxx–C7xxxx) and cast (C8xxxx–C9xxxx) compositions.

UNS Designation System

Copper alloys classified by composition and processing method.

View designations

C10000–C15999: Wrought coppers (99%+ Cu)
C16000–C19999: High-copper alloys with minor additions
C20000–C49999: Wrought brasses (Cu-Zn)
C50000–C52999: Phosphor bronzes (Cu-Sn-P)
C53000–C66999: Cu-Si and special alloys
C70000–C79999: Cu-Ni and Cu-Ni-Zn alloys
C80000–C99999: Cast coppers, brasses, bronzes

Common Alloy Families

Major copper alloy groups with distinct properties and applications.

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Pure copper: Excellent electrical/thermal conductivity
Brasses (Cu-Zn): Good strength and corrosion resistance
Phosphor bronzes (Cu-Sn-P): High fatigue strength
Aluminum bronzes (Cu-Al): High strength, corrosion resistant
Silicon bronzes (Cu-Si): Excellent welding characteristics
Copper-nickels (Cu-Ni): Marine corrosion resistance
Beryllium coppers (Cu-Be): Very high strength, non-sparking

Preparation Tips

Copper alloys are soft and prone to mechanical deformation during grinding.

View key considerations

Use lower grinding pressures to minimize subsurface damage and smearing
SiC papers preferred for initial grinding steps
Final polishing with colloidal silica or alumina produces excellent results
Copper alloys tarnish quickly. Etch promptly after final polishing
Clean thoroughly between preparation steps

Recommended Etchants

For PACE's full etchant catalog and the Materials Prep ELN, see Etchant Resources.

Etchant	Composition	Conditions	Applications
Ammonium Hydroxide / H₂O₂	Distilled water: 25 ml Ammonium hydroxide: 25 ml Hydrogen peroxide (3%): 5–25 ml	Immerse for seconds to minutes Use only fresh solution Rinse in water	Grain boundaries: use less H₂O₂ Grain contrast: use more H₂O₂
Nitric Acid Etch	Distilled water: 50 ml Nitric acid: 50 ml	Immerse for seconds to minutes Rinse in water Dry with alcohol	Copper and copper alloys General purpose etchant
Ferric Chloride Etch	Distilled water or ethanol: 100–120 ml Hydrochloric acid: 25–50 ml Ferric chloride: 5–10 g	Immerse for seconds to minutes Rinse in water Dry with alcohol	Produces grain contrast Effective for most copper alloys
Weck’s Copper Tint	Potassium permanganate: 12.5 g Sodium hydroxide: 5 g Distilled water: 250 ml	Immersion or swabbing at 20°C Rinse in water Dry with alcohol	Color contrast etching for copper alloys Color differentiation between phases
Klemm’s I Tint Etch	Saturated sodium thiosulfate: 50 ml Potassium metabisulfite: 1 g	Immerse for seconds to minutes Rinse in water; dry with alcohol	Phase identification in brasses and bronzes Alpha brass tints uniformly; beta phase remains brighter for clear two-phase contrast
Beraha’s Sulfide Tint	Hydrochloric acid: 1 ml Sodium thiosulfate: 12 g Distilled water: 240 ml	Immerse for 30–90 seconds Rinse in water; dry with alcohol	Color tint etch for copper alloys, especially multi-phase brasses Produces strong colors that distinguish alpha, beta, and gamma phases

Troubleshooting

Common etching issues and how to resolve them.

Over-etching

Surface appears too dark or grainy. Reduce etching time by 50% and monitor progress under the microscope.

Under-etching

Grain boundaries not clearly visible. Increase etching time by 15–30 seconds or ensure etchant is fresh.

Uneven Etching

Ensure sample is completely dry before etching and maintain consistent immersion or swabbing motion.

Rapid Tarnishing

Copper oxidizes quickly after polishing. Etch immediately after final polishing. Store samples in a desiccator.

Poor Contrast

Try Weck’s Copper Tint for color contrast, or adjust H₂O₂ concentration in the ammonium hydroxide etch.

Smearing Artifacts

If scratches or smearing visible after etching, re-polish using lighter pressure and finer abrasives, then re-etch.