How to Tell Copper from Copper-Nickel

1. Visual Inspection (Simplest First Step)

The most immediate difference is color, as the two materials have distinct hues that are easy to spot with the naked eye:

Pure Copper: Has a bright, distinctive reddish-orange or coppery-pink color-especially when clean or freshly polished. Over time, it tarnishes to a dull brown or greenish patina (known as "verdigris"), but the underlying metal remains reddish if scraped lightly.

Copper-Nickel: Has a muted silvery-gray or light bronze color, similar to stainless steel but with a warmer tone. It rarely develops a green patina; instead, it may darken slightly to a deeper silvery-gray over time, but never takes on copper's characteristic red-orange shade.

Tip: If the material is tarnished, gently scrape a small, inconspicuous area with a knife or sandpaper. Pure copper will reveal a bright reddish layer underneath, while copper-nickel will show a silvery-gray base.

2. Density Test (Relies on Weight and Volume)

Copper and copper-nickel have different densities, which affects how heavy they feel relative to their size. This test works best for small, solid pieces (e.g., coins, wires, small fittings):

Pure Copper: Density = ~8.96 g/cm³ (heavier for its size).

Copper-Nickel (e.g., 90/10): Density = ~8.80 g/cm³ (slightly lighter than pure copper, though the difference is subtle for small objects).

3. Magnet Test (Quick Elimination Tool)

While neither pure copper nor copper-nickel is ferromagnetic (they won't stick to a magnet), this test helps rule out other metals (e.g., iron, steel, or nickel-plated copper) that might be confused with them:

Pure Copper: Non-magnetic-no attraction to a standard fridge magnet.

Copper-Nickel: Also non-magnetic-no attraction to a magnet.

4. Hardness Test (Feels and Scratches)

Pure copper is softer than most copper-nickel alloys, which makes a difference in how easily they scratch or deform:

Pure Copper: Relatively soft-can be scratched easily with a steel nail or knife. It may also dent slightly if pressed firmly with a hard object.

Copper-Nickel: Harder and more rigid-resists scratching by a steel nail. It is less likely to dent under light pressure.

5. Chemical Test (For Definitive Confirmation)

For situations where visual or physical tests are unclear (e.g., plated metals or alloys with similar appearances), a simple chemical test using vinegar and salt can reveal the presence of pure copper:

How it works: Pure copper reacts with acetic acid (vinegar) and salt (sodium chloride) to form a blue-green copper acetate solution. Copper-nickel, with its lower copper content and nickel's resistance to this reaction, will not produce this color.

Observe the swab and the material:

Pure Copper: The swab will turn blue-green within 1–2 minutes, and the material's surface may develop a faint green tint.

Copper-Nickel: The swab remains white or light gray, with no color change on the material.

Note: This test is non-toxic and safe for home use, but avoid contact with eyes and wash hands afterward.