The ESDA process was originally discovered by Foster + Freeman more than 35 years ago and resulted in the founding of the company.Used by police forces and document examiners worldwide, ESDA instruments remain the systems of choice for the chemical-free and completely non-destructive detection of indented writing.
Foster + Freeman ESDA 2 treating a document.
The ESDA process was originally discovered by Foster + Freeman more than 35 years ago and resulted in the founding of the company.Used by police forces and document examiners worldwide, ESDA instruments remain the systems of choice for the chemical-free and completely non-destructive detection of indented writing.

ESDA®2

The industry-standard electrostatic imaging system for detecting indented writing

ESDA® works by creating an electrostatic image of indented writing, which is then visualized by the application of charge-sensitive toners. The sensitive imaging process reacts to sites of microscopic damage to fibres at the surface of a document, which have been created by abrasive interaction with overlying surfaces during the act of handwriting.

ESDA® is the ideal forensic tool. As well as being simple to operate, it produces positive, life-size transparencies of indented writing without damage or contamination to original documents and without interference to other forensic tests, and documents may be processed repeatedly without loss of sensitivity.

  • Creation of permanent records
  • Repeatable without loss of information
  • Effective on old documents
  • A3-sized document bed
  • Original cascade development method
  • Improved toner pad development
  • Optional aerosol hood for ‘powder cloud’ development
  • Replaceable vacuum bed
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Industry-Standard for more than 40 Years

Such is the level of success achieved by the Foster + Freeman ESDA, the terms ESDA and ‘the ESDA process’ has become industry standard terminology for the method of revealing indentations or impressions on paper.

The ESDA started life as part of a research project to develop a non-chemical, non-destructive method of identifying fingerprints on fabric, and while the project itself did not prove successful the ESDA’s secondary use, that of detecting indented writing on paper proved to be of huge interest to document examiners worldwide.

The ESDA technique works by an electro-static process, in much the same way as a photocopier. The sheet of paper to be investigated is placed on a bronze plate that has been perforated by tiny holes and earthed. Underneath the slab is a pump, which, when switched on, sucks air through the plate and holds the paper down flat against it. A sheet of transparent polymer film is laid over the top of the paper which is then charged with static electricity: a metal wand known as the corona discharge unit is passed over it. Inside the wand is a thin wire with a potential of about 5,000 volts. As a result, static electricity discharges itself to earth through the bronze plate.

The conductivity of the paper and film laid across the plate differs at those places where there are indentations in the paper, this difference results in an electronic image of the indentations being created on the sheet of film. This image is then developed by allowing fine carbon granules to spread over it, either by an aerosol process in a cloud chamber or by pouring carbon granules, mixed with small plastic balls which act as a carrier, across the surface of the paper. The granules stick to the electrostatic image of the indentations, and the image becomes visible.

A Breakthrough Case

The ESDA went from being a research project to an essential piece of document examination equipment almost overnight when, following a raid on a London bank, police used the ESDA technique to examine a note handed by the robber to the bank teller demanding cash. Hidden to the naked eye but revealed by the ESDA were the indentations of a telex message drafted to someone in Canada and pleading for money to be sent to an address in Surrey. The man was arrested and the story hit the headlines. News of the ESDA’s capabilities spread fast.

With strong backing from the UK Home Office, Doug Foster and Bob Freeman set up in partnership making the first run of ESDA devices from the garage at Doug’s home.