Davis Reagent
Definition
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 is too aggressive.
- Primary application
- Restoration of erased serial numbers and markings on metal surfaces
- Substrate specificity
- Steel and aluminium alloy (each requires different formulation)
- Action rate
- Slower than Fry's reagent, allowing controlled contrast development
Common questions
When would I use Davis reagent instead of Fry's reagent?+
Davis reagent acts more slowly than Fry's, making it useful when Fry's produces too aggressive or overwhelming contrast on steel. The gentler etching action gives you finer control over how the erased markings become visible.
Does Davis reagent work on all metals?+
No. The formula varies by substrate. For steel, it uses cupric ammonium chloride in dilute HCl. For aluminium alloys, a different formulation uses lower-concentration HCl and copper chloride to account for the passive oxide layer on aluminium's surface.
Why is the chemistry different for aluminium?+
Aluminium forms a protective passive oxide layer that steel doesn't have. Davis reagent for aluminium is formulated with lower HCl concentration and adapted copper chloride chemistry to work effectively through this oxide barrier.
Related terms
- Fry's Reagent
- Classical etchant for plain carbon and low-alloy steel: 40 g cupric chloride (CuCl2) + 90 mL concentrated HCl + 100 mL water....
- ASTM E2885-13
- ASTM International standard practice for restoration of obliterated vehicle identification numbers; the reference protocol for VIN casework in US and internationally aligned...
- Backscattered Electron (BSE) Imaging
- An SEM imaging mode sensitive to atomic number and crystallographic texture; can reveal grain-boundary elongation patterns in the sub-surface cold-worked zone after...
- Cold-Working Stress Field
- Residual plastic deformation and elevated dislocation density in a metal lattice created by stamping; persists below the visible surface even after surface...
- Electrolytic Etching
- Electrochemical alternative to chemical etchants. The part is the anode in an electrolyte bath; controlled current selectively dissolves the strained metal at...
- Heat-Tinting
- Restoration by controlled heating of the polished surface. Strained metal oxidises at a different rate from unstrained metal, producing colour contrast (straw...
- INTERPOL iARMS
- INTERPOL's Illicit Arms Records and tracing Management System. Multilateral database enabling law enforcement in INTERPOL member countries to trace recovered or seized...
- Magnetic Particle Inspection (MPI)
- A non-destructive testing method that reveals magnetic-domain contrast between cold-worked and unstressed zones in ferromagnetic metals using a ferrofluid under UV illumination;...
- 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...
- Neutron-Induced X-Ray Fluorescence (NIXRF)
- A synchrotron-based method using neutrons to probe deep obliterations; can detect digit geometry buried several millimetres beneath a machined surface, entirely non-destructively.
- Peak Contrast
- The narrow window during a chemical etch when the original digits are most legible. Continuing past peak contrast overetches the unstrained metal...
- Profilometry
- White-light interferometry or confocal laser scanning to detect nanometre-scale height differences on a metal surface; can reveal topographic ghost images of obliterated...
Explained in these topics
- Restoration of Erased Markings on Metal SurfacesVariant 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 is t...
- Restoration of Erased Serial NumbersA lower-concentration hydrochloric acid and copper chloride solution formulated for aluminium alloy substrates, where the passive oxide layer requires adapted...