A. Sulfuric Acid (H₂SO₄) Test Nickel: Dissolves slowly, producing hydrogen bubbles. Chromium: Resists sulfuric acid (no bubbles). B. Copper Sulfate Test Nickel: Immerse in 5% CuSO₄ solution → No copper deposition (nickel is more noble than copper).
Determining whether a workpiece is nickel-plated or chromium-plated can be done through several methods, ranging from simple visual and physical tests to advanced analytical techniques. Below is a step-by-step guide to help you distinguish between the two coatings:
Color: Typically has a slightly yellowish, silver-white or warm gray appearance.
Finish: Can range from semi-bright to matte, depending on the process (electroless nickel is often more uniform and duller than electroplated nickel).
Reflectivity: Less reflective than chromium unless polished.
Color: Bluish-white, mirror-like shine (decorative chrome) or slightly duller gray (hard chrome).
Finish: Extremely smooth and reflective (if decorative) or micro-cracked/harder (if industrial hard chrome).
Visual Clue: Chrome is often applied over a nickel underlayer, so if you see peeling, the underlying nickel may be exposed.
Nickel:
Pure nickel (electroplated) is magnetic.
Electroless nickel (Ni-P or Ni-B) is non-magnetic (unless heat-treated).
Chromium: Non-magnetic in all forms.
Note: If the part is magnetic, it’s likely nickel (unless the base metal is ferrous).
Nickel:
Electrolytic nickel: 150–300 HV (soft, can be scratched with a knife).
Electroless nickel (Ni-P): 500–700 HV (harder, resists scratching).
Chromium:
Decorative chrome: 600–1000 HV.
Hard chrome: 800–1200 HV (much harder than nickel).
Method: Use a Rockwell or Vickers hardness tester or a file test (chrome resists filing).
Nickel:
Apply a drop of dilute nitric acid (HNO₃) → Turns greenish (due to nickel dissolution).
Chromium:
Nitric acid has little to no reaction (chrome is highly corrosion-resistant).
Nickel: Dissolves slowly, producing hydrogen bubbles.
Chromium: Resists sulfuric acid (no bubbles).
Nickel:
Immerse in 5% CuSO₄ solution → No copper deposition (nickel is more noble than copper).
Chromium:
Copper will not deposit on chrome either, but if the coating is worn, copper may plate on exposed nickel underlayer.
Non-destructive, identifies elemental composition:
Nickel coating → Shows Ni peaks (may include P or B if electroless).
Chromium coating → Shows Cr peaks (may show underlying Ni if double-layered).
Provides cross-sectional analysis to confirm layering (e.g., Cr over Ni).
Measures corrosion potential (Nickel is less noble than chromium).
Nickel Plating:
Used for corrosion resistance, wear resistance, and as an undercoat (e.g., automotive trim, electronics, industrial parts).
Chromium Plating:
Decorative: Bright, shiny surfaces (e.g., faucets, car bumpers).
Hard Chrome: High-wear applications (e.g., hydraulic rods, gun barrels).
| Test | Nickel Plating | Chromium Plating |
|---|---|---|
| Color/Finish | Warm gray, semi-bright | Bluish-white, mirror-like |
| Magnetic Response | Magnetic (pure Ni) / Non-magnetic (EN) | Non-magnetic |
| Hardness | Softer (electrolytic) / Harder (EN) | Extremely hard |
| Acid Reaction | Dissolves in HNO₃ (greenish) | Resistant to HNO₃ |
| XRF Analysis | Shows Ni (may have P/B) | Shows Cr (may have Ni underlayer) |
Start with visual/hardness tests (easiest for quick checks).
Use chemical spot tests if no equipment is available.
For 100% certainty, use XRF or SEM/EDS.