Electrostatic Detection Apparatus (ESDA)
A sensitive technique used to identify indented and/or electrostatic impressions on documents caused by other documents having been written upon whilst resting on top of the document under investigation.
The technique of ESDA Sequencing (determining whether writing impressions are on top of or underneath inked writing on a page) was developed by this Laboratory and can provide important information as to the sequence in which documents were actually prepared
This technique is highly sensitive and may reveal impressions not only from writings on the page immediately resting on top of the document in question but also two, three or even four pages above the sheet of paper under investigation.
This technique regularly gives valuable information as to:
- The source or history of the document.
- Association with other documents.
- Information as to the sequence of production of writings or documents.
- Identification of documentation produced en masse.
- Identification of purportedly unrelated documents having been written/signed on top of one another.
- Identification of impressed tracing guidelines around an inked signature.
Regrettably ESDA impressions are affected by certain conditions. To preserve ESDA impressions one should ensure that:
- The document is handled as little as possible as fingerprints can mask or destroy writing impressions.
- The document should not be treated with a chemical fingerprinting agent prior to ESDA being undertaken.
- The document should not be subjected to excessive humidity, liquids etc.
- The document should be preserved preferably between two sheets of paper within either a plastic or cardboard wallet.
- If a document is sent to us, the envelope must be addressed before the document in dispute is placed inside.