Erasure (Chemical)
Definition
Removal of ink by bleaching or oxidising agents such as sodium hypochlorite, chloramine T, oxalic acid, potassium permanganate or hydrogen peroxide. Leaves a residual ghost image and disturbs paper fluorescence.
- Agents
- Sodium hypochlorite, chloramine T, oxalic acid, potassium permanganate, hydrogen peroxide
- Residual sign
- Ghost image, disturbed fluorescence
- Detection tools
- UV and IR examination, fluorescence imaging
Common questions
Why does chemical erasure often remain detectable even when the ink is no longer visible?+
The bleaching agents alter the paper's fibres and surface chemistry as well as the ink, which changes how the treated area fluoresces or absorbs infrared light compared with untouched paper, revealing the area even without visible residue.
How is chemical erasure distinguished from mechanical erasure on examination?+
Chemical erasure typically shows altered fluorescence and a faint ghost image with the paper surface intact, while mechanical erasure shows physical fibre disturbance, thinning and loss of surface gloss without the same fluorescence change.
Related terms
- Addition (Interlineation, Insertion)
- Fresh writing squeezed between lines, in margins, after the last entry, or in blank spaces left in the original document. Often shows...
- Alteration
- Any change made to a document after its original execution, including erasure, obliteration, addition, substitution and overwriting. A material alteration changes the...
- Erasure (Mechanical)
- Physical removal of writing by rubber, knife, scalpel blade, sandpaper or eraser. Disturbs paper fibres, thins the paper, and lifts the sizing...
- ESDA
- Electrostatic Detection Apparatus; detects latent indentations in paper by charging the surface and cascading toner particles, revealing tracing stylus pressure and writing...
- IR Luminescence
- Emission of near-infrared radiation by ink dye molecules when excited by visible light; different ink formulations luminesce at different intensities, allowing differentiation...
- Obliteration
- Covering of existing writing with an opaque layer (ink, correction fluid, or correction tape) so that the underlying text is invisible in...
- Overwriting
- Tracing over an original stroke with a fresh stroke, usually to change a digit or letter. Detected by stroke thickness, hesitation, and...
- VSC-8000
- Video Spectral Comparator by Foster + Freeman, the standard QD instrument in CFSL and GEQD labs, with broadband visible, UV (254, 365...