Introduction

t Document Evidence we possess equipment and techniques that enable us to undertake examinations to determine:

• Whether a document has been completed using more than one ink.
  
• Whether any alterations have been made to a document - such as changing a date or altering an amount.
  
• What is present underneath an obliterated entry - the obliteration could have been made by scribbling over with a pen or by using correction fluid.
  
• The sequence in which intersecting lines have been written. Tthis can be useful, for example, in determining whether one signature was added before or after another one.
  
• Under advantageous conditions, the text of a pencil entry that has been subsequently erased.
  

The Technique
The main apparatus used at Document Evidence for these examinations is a Projectina Docucenter 3000. This machine allows documents to be examined using illumination restricted to selected parts of the infra-red, visible or ultra-violet portions of the light spectrum. It is a well established property of writing inks that while some may appear similar in colour to one another in normal visible light, they can exhibit very different appearances when viewed using more specific portions of the light spectrum. This is a consequence of differences in the mixtures of dyes used to make the inks.

The Docucenter 3000 incorporates an infra-red sensitive video camera connected to a monitor that allows the differences in inks to be observed and recorded. It also has a facility that allows light to be transmitted through a document; this can be useful in deciphering obliterations.

It should be noted however that where inks are indistinguishable it does not necessarily follow that the same individual pen was used since pens containing the same ink are manufactured in large numbers. In addition there are no reliable techniques for establishing the absolute age of an ink entry nor for determining the relative ages of entries which are made within a short period of time.