Beraha's Etchant
Beraha's Reagent
Material Specific
Composition
Sodium thiosulfate 5–15%, Potassium metabisulfite 2–5%
PACE product, by weight
Method
Immersion
Time
30–120 s
Alternative Names
Tags
Reveals
Color tinting of ferrite, pearlite, martensite, bainite, and retained austenite (orientation- and composition-dependent)
Typical Results
Beraha's tint etchant: sodium thiosulfate + potassium metabisulfite in water. More dilute than Klemm's (5–15% thiosulfate vs 25–50%); gives finer, slower-developing color contrast. Used on carbon and low-alloy steels for Q&T microstructure visualization. It distinguishes ferrite (cyan/orange) from martensite (brown) from bainite (intermediate), with retained austenite remaining unstained.
Application Method
Method:Immersion
Typical Time:30–120 s
Preparation Notes
PACE Beraha's Reagent is supplied ready-to-use. Composition (by weight):
| Ingredient | CAS No. | % | Hazardous |
|---|---|---|---|
| Sodium thiosulfate | 7772-98-7 | 5–15% | Yes |
| Potassium metabisulfite | 16731-55-5 | 2–5% | Yes |
| Water | 7732-18-5 | 85–95% | No |
Application Notes
Polish to 0.05 µm or VibroMet. Immerse 30–120 s; watch in real time and pull when contrast is sharpest. Rinse with water then ethanol; air-dry only (no compressed air, which re-deposits residue).
Troubleshooting
The polish must be perfect; any scratch shows as a colored line. Over-developed: repolish with 0.3 µm and re-etch shorter. Slower than Klemm's: extend time rather than concentrating.
Storage Notes
Amber glass, refrigerated. Stable a few weeks; discard when cloudy.
Alternative Etchants
- Klemm's Reagent (more aggressive thiosulfate)
- Weck's Etch (Al/Mg)
- Lichtenegger-Bloech
Similar Etchants
- Klemm's Reagent