ESDA
Definition
Electrostatic Detection Apparatus; detects latent indentations in paper by charging the surface and cascading toner particles, revealing tracing stylus pressure and writing from overlying sheets.
- Developer
- Foster and Freeman (UK, 1979)
- Key strength
- Recovers latent indented impressions without altering the evidence document
Common questions
What does ESDA stand for and what does it do?+
ESDA stands for Electrostatic Detection Apparatus. It reveals indented writing impressions left on documents without damaging them. When you write on a notepad, the stylus presses into multiple sheets below. ESDA can recover those hidden indentations from underlying pages, which is useful in forgery detection and document fraud investigation.
How does ESDA work technically?+
ESDA uses a four-step process. First, the paper is humidified slightly to make the indentations more receptive. A mylar film is then laid over the surface. The surface is then charged with static electricity via corona charging. Finally, toner particles cascade across the surface and collect in the charged indentation marks, making them visible and photographable.
What kinds of document fraud can ESDA help detect?+
ESDA is particularly useful for revealing rewritten cheques, tracing stylus pressure in suspected forged signatures, and discovering missing pages in pads by showing writing from overlying sheets on the page below.
Related terms
- 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...
- VSC-8000
- Video Spectral Comparator by Foster + Freeman, the standard QD instrument in CFSL and GEQD labs, with broadband visible, UV (254, 365...
- 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...
- Auto-Forgery
- A genuine signature executed by the legitimate signer on a document they later deny, undetectable by handwriting comparison alone; requires document-dating and...
- Charred Document
- Paper that has been burned to the carbonised stage but not fully reduced to ash; the cellulose has pyrolysed and the sheet...
- Erasure (Chemical)
- Removal of ink by bleaching or oxidising agents such as sodium hypochlorite, chloramine T, oxalic acid, potassium permanganate or hydrogen peroxide. Leaves...
- Erasure (Mechanical)
- Physical removal of writing by rubber, knife, scalpel blade, sandpaper or eraser. Disturbs paper fibres, thins the paper, and lifts the sizing...
- Exemplar Set
- The collection of known genuine signatures used as the comparison baseline; SWGDOC and ENFSI guidelines specify a minimum of 20-30 exemplars spanning...
- Freehand Simulation
- A forgery produced by visually studying the target signature and reproducing it from memory, without mechanical tracing; characterised by slow pen speed,...
- 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...
- Indentation
- Latent pressure impression left on a lower sheet of paper when writing on an upper sheet; depth depends on pen pressure, paper...
Explained in these topics
- Examination of Alterations: Erasures, Obliterations and AdditionsElectrostatic Detection Apparatus by Foster + Freeman. Develops latent indented impressions on the page below the one that was written on, exposing missing pag...
- Indentations, Secret Writings and Charred DocumentsElectrostatic Detection Apparatus. Developed by Foster + Freeman (UK, 1979) to visualise indented impressions via humidification, mylar film, corona charging a...
- Reproduction of Documents: Photographic and Mechanical MeansElectrostatic Detection Apparatus (Foster + Freeman ESDA-2). Detects indented writing on the underlying sheets of a pad without altering the document.
- Signature Examination: Genuine, Simulated, Traced and Auto-ForgeryElectrostatic Detection Apparatus; detects latent indentations in paper by charging the surface and cascading toner particles, revealing tracing stylus pressur...