Klemm's Etchant
Klemm's Reagent
Material Specific
Composition
Sodium thiosulfate 25–50%, Potassium metabisulfite 5–10%
PACE product, by weight
Method
Immersion
Time
40–120 s
Alternative Names
Tags
Reveals
Color tinting of ferrite, pearlite, martensite, bainite, retained austenite (orientation- and composition-dependent); grain and twin contrast in brass and zinc; phase distinction in Mg alloys
Typical Results
Classical Klemm's I: sodium thiosulfate + potassium metabisulfite. The standard tint etchant for steel microstructure visualization. Higher thiosulfate concentration than Beraha's (25–50% vs 5–15%); produces stronger color contrast. Distinguishes ferrite, pearlite, martensite, bainite, and retained austenite by color. Also used on brass, zinc, and magnesium. NOT a stainless-steel tint; use Beraha's or Lichtenegger-Bloech for stainless.
Application Method
Method:Immersion
Typical Time:40–120 s
Preparation Notes
PACE Klemm's Reagent is supplied ready-to-use. Composition (by weight):
| Ingredient | CAS No. | % | Hazardous |
|---|---|---|---|
| Sodium thiosulfate | 7772-98-7 | 25–50% | Yes |
| Potassium metabisulfite | 16731-55-5 | 5–10% | Yes |
| Water | 7732-18-5 | 70–85% | No |
Application Notes
Polish to 0.05 µm or VibroMet. Immerse 40–120 s; watch in real time and pull when contrast is sharpest. Rinse with water then ethanol; air-dry only (no compressed air).
Troubleshooting
Polishing scratches show as colored lines; the polish must be perfect. Color over-developed: repolish with 0.3 µm and re-etch shorter. If slow, the thiosulfate has partly oxidized; replace the bottle.
Storage Notes
Amber glass, refrigerated. Stable a few weeks once opened; discard when cloudy or dark.
Alternative Etchants
- Beraha's Reagent (more dilute thiosulfate)
- Weck's Etch (Al/Mg)
- Lichtenegger-Bloech
Similar Etchants
- Beraha's Reagent