Stamped Marking
Definition
A serial, chassis, engine or part number impressed into metal by a hardened steel die under high force. The visible impression is shallow, but the plastic deformation it produces extends 2 to 5 times deeper into the metal as a strained sub-surface zone.
- Method
- Hardened steel die driven by hydraulic or hand-hammer force
- Visible depth
- Shallow compared to the deformation zone beneath it
- Deformation zone
- 2 to 5 times deeper than the visible impression
- Restoration target
- Strained sub-surface grain, not the removed surface
Common questions
Why can a stamped number be restored after the surface is filed off?+
Filing removes the visible impression but not the strained metal grain beneath it. Etchants attack that strained zone faster than undisturbed metal, so the original digits re-emerge as a visible pattern even though the surface itself is now flat and featureless.
How deep can a die impression be ground before restoration becomes impossible?+
Once grinding or filing removes metal past the full depth of the plastic deformation zone, no strained grain remains to react preferentially with an etchant, and no chemical or magnetic method can recover the number.
Related terms
- Davis Reagent
- Variant etchant for steel using cupric ammonium chloride (Cu(NH4)2Cl4) in dilute HCl. Slower acting than Fry's, sometimes preferred when contrast on Fry's...
- Fry's Reagent
- Classical etchant for plain carbon and low-alloy steel: 40 g cupric chloride (CuCl2) + 90 mL concentrated HCl + 100 mL water....
- Heat-Tinting
- Restoration by controlled heating of the polished surface. Strained metal oxidises at a different rate from unstrained metal, producing colour contrast (straw...
- Magnetic-Particle Method
- Non-destructive restoration for ferromagnetic metals. The polished surface is magnetised and dusted with fine iron particles; the particles cluster at the strained...
- Peak Contrast
- The narrow window during a chemical etch when the original digits are most legible. Continuing past peak contrast overetches the unstrained metal...
- Strained Zone
- The region of cold-worked, plastically deformed metal lying beneath an original stamp. The crystal lattice is distorted, dislocation density is elevated, and...
- Villela's Reagent
- Etchant for stainless and high-chromium steels: 1 g picric acid + 5 mL concentrated HCl + 100 mL ethanol. Targets prior austenite...