Barker's EtchantElectrolytic Barker's
Barker's Reagent (Electrolytic)
Electrolytic
Composition
Fluoboric Acid (HBF₄)
Concentrated
Method
Electrolytic anodizing
Time
30–120 s at 20–30 V DC
Alternative Names
Tags
Reveals
Grain orientation contrast under polarized light. The anodic film thickness varies with crystal orientation, producing strong color separation between grains
Typical Results
The best aluminum grain-structure etchant for wrought and cast alloys. Builds a transparent anodic film whose interference color in polarized light depends on grain orientation. Standard for grain-size measurement in 1xxx through 7xxx alloys and Al castings.
Application Method
Method:Electrolytic anodizing
Typical Time:30–120 s at 20–30 V DC
Preparation Notes
CAUTION: Fluoboric acid is corrosive. Use concentrated fluoboric acid (HBF₄) as electrolyte. Use in fume hood with proper PPE.
Application Notes
Sample anode; aluminum or stainless cathode. Apply 20–30 V DC at ~0.2 A/cm² for 30–120 s in 5 mL HBF4 + 200 mL H2O. Rinse with water. View under polarized light with a sensitive tint plate (lambda plate).
Troubleshooting
Colors only visible under polarized light + sensitive tint plate. Under-etch: film too thin, weak colors; increase voltage or time. Over-etch: film burns and pits; reduce voltage.
Storage Notes
PE bottle. Contains HBF4; store cool, separate from acids and bases.
Alternative Etchants
- Keller's Reagent
- 0.5% HF
Similar Etchants
- Anodizing-type electrolytic etches