ASTM No. 2

General Purpose

Composition

4g Picric Acid, 100ml Ethanol

Method

Immersion

Time

10s

Alternative Names

Pearlite, cementite, grain boundaries

ASTM standard etchant for revealing pearlite structure. Does not attack ferrite grain boundaries as strongly as Nital.

Pearlite darkens, ferrite remains light

Method:immersion

Typical Time:10 seconds

Mix 4g picric acid with 100ml ethanol. Warm slightly to dissolve. CAUTION: Picric acid is explosive when dry. Keep wet at all times.

Immerse sample for 10-20 seconds. Swab if needed. Rinse with ethanol then water.

Keep picric acid wet at all times. Never allow to dry. Store in water-wet condition. If over-etched, reduce time.

Store in dark bottle, keep wet. Add water if solution dries. Extremely hazardous when dry. Never allow to dry completely.