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  • Elisabeth Briggs

ESDA - How to reveal secret writing: Part 1

Writing on one sheet of paper resting on another produces impressions on the surface below. Did you know it is possible to visualise these impressions and produce a permanent image?

The Electrostatic Detection Apparatus, ESDA, was developed in the 1970s, by accident, as part of a research project attempting to visualise fingerprints on fabric. Whilst the intended project was not successful, it did prove effective at detecting intended writing on paper. Further details can be found at - Foster & Freeman is the company that was established to produce the first ESDA commercially.

The ESDA technique is now a vital tool for all forensic document examiners.

ESDA can be used to reveal:

  • Intelligence information from documents, for example impressions of names, or an addressed letter, on an anonymous note

  • Evidence that a signature has been traced

  • Clues that text has been erased from the paper surface

  • Information about previous versions of a document that has been rewritten - one of the most famous cases involved interview notes relating to the Birmingham Six

Traditional methods to reveal indented writing are pencil shading or oblique light. However pencil shading destroys the document, and oblique light is simply not practical for a large document.

Pencil shading to show indented writing
Pencil shading shows indented writing
Oblique lighting to show indented writing
Oblique lighting shows indented writing

ESDA can show indented impressions as dark writing in a way that can be preserved as a permanent image. The document will not be harmed and the process can be repeated again and again. It can also reveal impressions from several pages underneath the 'original' writing.

ESDA image showing indented writing
ESDA image showing indented writing

Further QDE blog posts will describe the ESDA process in more detail, outline limitations of the technique and provide more examples.

A sneak preview of the process is shown here - to be described step-by-step in a future post:


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