CHARRED DOCUMENTS 

The handling and decipherment of charred documents is one of the perplexing problems in the field of questioned document and arson investigation. A burnt document is exceedingly fragile and requires extreme care in handling and in processing. Then too, its blackened, carbonized state renders ordinary restorative processes ineffectual. An entirely new approach to a unique problem is required.

Charred papers vary in physical composition and are burned under many different conditions. It is not to be expected that all will react the same when treated. The document examiner and laboratory technician may find it necessary to attempt several of the methods before finding one that will achieve a successful result:

1. Infrared photography — In infrared photography, the film or image sensor used is sensitive to infrared light. The part of the spectrum used is referred to as near-infrared to distinguish it from far-infrared, which is the domain of thermal imaging. Wavelengths used for photography range from about 700 nm to about 900 nm. Film is usually sensitive to visible light too, so an infrared-passing filter is used; this lets infrared (IR) light pass through to the camera, but blocks all or most of the visible light spectrum (the filter thus looks black or deep red). («Infrared filter» may refer either to this type of filter or to one that blocks infrared but passes other wavelengths.)
2. Reflecting lighting off the paper’s surface at different angles in order to contrast the writing against the charred background.
3. Digital imaging: Digitize the image by a scanner or a digital camera and then adjust it by an image-editing program (ex. Adobe Photoshop) by lightening, darkening and color and contrast controls.

Documents that may contain indented impressions not visible to the naked eye can be visualized through the use of an Electrostatic Detection Device (EDD) such as the Electrostatic Detection Apparatus (ESDA). An EDD uses applied charges and toner to visualize areas of indented writing, making them visible to the eye. The ESDA uses the principle that indented areas of the document carry less negative charge than surrounding areas. This causes the toner used in the EDD to be attracted to these areas, revealing indentations that are present.

Being asked to distinguish between two or more inks that may have been used to alter a document, is a common problem posed to the Forensic Document Examiner. Additions and/or obliterations in most cases are made with ink of the same color as the original entries. Once the authenticity of a document has been questioned where an important entry has been obliterated, damaged or faded, a possible unauthorized alteration has been made or simply verifying only one ink was used to complete the document, the examiner is challenged with determining, preferable using nondestructive techniques.

Modern inks are a combination of synthetic or natural dyes or pigments held in suspension, along with a volatile solvent. The resultant color may be the result of a single coloring agent or a mixture of several dyes and/or pigments. And, depending on the different coloring agents used, the reaction to light stimulus (visible and non-visible) will vary.

When ink is exposed to a specific range of light spectrum (infrared or visible), three different reactions can occur:
1. The light, all or partial, will be reflected by the ink. This will cause the ink to appear paler or to disappear.
2. The ink will absorb the light and convert it to heat or undergo structural or chemical changes. The result is the ink will appear darker.
3. The light will be absorbed by the ink and then be re-emitted at a different wavelength, a process known as “infrared Luminescence”. The ink will brighten or appear to “glow” when visualized in the infrared region.

The amount that each component of a mixture travels can be quantified using retention factors (Rf). The retention factor of a particular material is the ratio of the distance the spot moved above the origin, and the distance the solvent front moved above the origin. It can be calculated using the formula: 

The Rf values for each of the components in the previous example can be calculated: 

Notice that (1) the bigger the Rf, the further the spot moved and (2) that the Rf should be the same for a component regardless of how far the solvent moves.

Retention factors are useful in comparing the results of one chromatogram to the results of another. If the conditions in which the chromatogram are run are unchanged (same mobile and stationary phases), the retention factor for a given material should remain constant. This allows unknowns to be compared to known materials. If the retention factor of an unknown does not match that of a known material, they are not the same compound. Similar retention factors suggest that the two samples could be the same, but is not proof. In reality, the retention factors will vary slightly from sample to sample. Interactions of the individual components with each other and the concentration of the component in the sample will both affect the Rf value. 

• Fiber identification
• General appearance
• Color
• Weight
• Watermarks
• Additives
• Fillers
• Density
• Thickness
• Age.

• Lead
• Hardness Scale: a traditional measure of the hardness of the «leads» (actually made of graphite) in pencils. The hardness scale, from softer to harder, takes the form: 3B, 2B, B, HB, F, H, 2H, 3H, 4H; with the standard «number 2» pencil being of hardness 2H.