Forgers often attempt to remove, add, or change portions of written documents for widely varied reasons that range from financial gain to creating an alibi. Alterations can be as simple as changing a date or as complex as attempting to erase and rewrite signatures or portions of documents. These changes are called erasures, obliterations, and alterations.
Wiping away writing
Text that doesn't suit the criminal's needs may simply be erased using a rubber eraser, a knife point or other sharp instrument, sandpaper, or even a fingernail — anything that scrapes or rubs away unwanted marks. You often can easily see erasures with the naked eye, but even when alterations aren't readily apparent, forensic examiners have the following investigative tools at their disposal:
A simple magnifying glass or a microscope used with oblique (angled) lighting uncovers most erasures.
Ultraviolet or infrared light may expose tiny fragments of eraser and ink nestled into the fibers of the paper whenever someone uses a rubber eraser.
Lycopodium powder, when dusted over the page, clings to and exposes tiny rubber particles and eraser fragments that invariably remain after erasures.
Exposing erasures is important because, even if the examiner can't see the original words or marks, erasures reveal that someone altered the document, which in and of itself may be proof of a crime and render many legal documents null and void.
Eradicating the original
One way to destroy a document is to obliterate the paper on which it's written. Criminals typically use fire for this purpose. After the paper burns, the writing is lost forever, right? Well, not exactly. If the paper is charred but still intact, reflecting light at various angles off the paper's surface might expose the contrast between the ink and the charred paper background. The page then can be photographed.
Handling charred pages, however, is extremely difficult because they're delicate and easily crumble. Spraying them with a solution of polyvinyl acetate in acetone is one way around this problem. Doing so stiffens the paper and makes handling it much easier. Examiners then float the treated pages on a solution of alcohol, chloral hydrate, and glycerin and photograph them. Alternatively, forensic workers sandwich the pages between two photographic plates and place them in a darkroom for two weeks. They then develop the plates, which may reveal the writing.
Criminals sometimes use chemicals, such as oxidizing or bleaching agents, to remove writing. These chemicals react with ink by producing a colorless compound, and the writing disappears. Well, it almost disappears. Using a microscope, an examiner may see remnants of the ink and even a discoloration in the area where the paper was treated.
Using a laser is another modern method of obliterating writing. Although the laser vaporizes the ink, it also burns nearby paper fibers, and the damage shows up under a microscope.
Often, a simple obliteration of words or marks doesn't completely serve the forger's needs, so further alteration by replacing obliterated words or numbers with others is required. Common examples are changing the amount of a check or the date on a contract or will.
Whenever someone obliterates writing before adding changes, an examiner can see the changes in the underlying paper and analyze the new writing by comparing it with the old for differences in technique. Sometimes, the forgery is so well done that a simple inspection doesn't reveal any changes. Fortunately, the examiner has other tools in his bag of tricks.
Under the microscope, subtle differences between the original and altered portions of the writing may appear. Slight changes in ink color, line thickness, and pen pressure, as well as double lines, often become visible. If the forger used a ballpoint or roller ball pen, distinguishable marks from defects in either type of pen point may show up.
Overwriting is another form of forgery in which the forger doesn't erase anything but rather adds to or overwrites a portion of a document. Maybe a 1 is changed to a 9, or a 0 is added to a check. If the forger uses the same ink that was used to prepare the original document, these types of changes can be extremely difficult to uncover. But forgers don't often have access to the pen or ink that was used for the original writing, so they make do with a similar pen and ink color. Careful examination of the differing ink might reveal areas that have been altered.
Although two inks may seem identical under normal light, they usually appear much different when exposed to ultraviolet (UV) or infrared light. Each ink reacts differently to UV light; one may fluoresce, and the other may fade from view. Infrared photography, which basically means photographing the page under a blue-green light with infrared-sensitive film, often clearly distinguishes between two kinds of ink.
If these lighting techniques don't provide any help, the examiner may have to examine the chemical contents of the inks to show that they are indeed different.