Peak Contrast
Definition
The narrow window during a chemical etch when the original digits are most legible. Continuing past peak contrast overetches the unstrained metal and erases the recovered pattern, which is why interval photography is mandatory.
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...
- Stamped Marking
- A serial, chassis, engine or part number impressed into metal by a hardened steel die under high force. The visible impression is...
- 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...
Explained in
- Restoration of Erased Markings on Metal SurfacesThe narrow window during a chemical etch when the original digits are most legible. Continuing past peak contrast overetches the unstrained metal and erases th...