Indentation
Definition
Latent pressure impression left on a lower sheet of paper when writing on an upper sheet; depth depends on pen pressure, paper thickness and number of intervening sheets.
- Cause
- Pen pressure transmitted through paper to sheets beneath
- Visibility
- Not visible under normal room light
- Depth factors
- Pen pressure, paper thickness, number of sheets
- Detection tools
- Oblique lighting, ESDA
Common questions
How far below the written sheet can indentations still be recovered?+
Legible indentations have been recovered several sheets down a notepad, though depth and clarity fall off quickly, so examiners test each sheet individually rather than assuming only the immediate next page carries usable detail.
Does photocopying or scanning a document destroy the indentations in the original?+
No, indentations are a physical deformation of the paper fibres, not an image on the surface, so copying does not erase them and the original sheet must still be preserved and examined for ESDA testing.
Related terms
- Charred Document
- Paper that has been burned to the carbonised stage but not fully reduced to ash; the cellulose has pyrolysed and the sheet...
- ESDA
- Electrostatic Detection Apparatus; detects latent indentations in paper by charging the surface and cascading toner particles, revealing tracing stylus pressure and writing...
- Glycerin Chamber
- Sealed humidification chamber held at 60 to 80 percent relative humidity using glycerin-water solutions to restore flexibility to charred or brittle paper...
- Oblique Light
- Side lighting at a low angle (5 to 15 degrees from the paper plane) that throws indentation shadows. The simplest indented-writing technique,...
- PVA Spray
- Polyvinyl-acetate solution sprayed in a fine mist to consolidate the surface of a charred sheet so it can be handled, mounted and...
- Secondary Writing
- Term for indented impressions: writing recovered from a sheet beneath the original, also called secondary or transferred writing.
- Steganography
- Concealing one file inside another in a way that hides the existence of the hidden file. LSB image manipulation, JPEG DCT coefficient...
- Sympathetic Ink
- Older name for invisible ink; the writing develops (becomes 'sympathetic') only after a heat, chemical or UV stimulus is applied.
- VSC
- Video Spectral Comparator (Foster + Freeman VSC-8000 series). Workhorse QD instrument combining UV, visible and IR sources with IR-sensitive cameras for ink,...