When visiting a crime scene, if the investigator finds a document as evidence, he will carefully collect and preserve the document. He will send it to the laboratory for its paper and ink analysis through a maintained chain of custody. This article will learn about the methods used for paper analysis and ink analysis.
Paper analysis and ink analysis of the document helps us to find out the estimated age of writing. This allows us to lead the investigation of a criminal case in the right direction. Several methods for ink analysis are UV-Visible spectroscopy, infrared spectroscopy, chromatography, neutron activation analysis, and visual spectral comparator. Examination of paper is done by visualization, chemical test, sizing agents, special paper micrometre, etc. We’ll study them in further sections.
Along with the topics discussed above, we’ll also study the age of writing, which uses the paper and ink examination method for determining its estimated age.
Some questioned document cases where the issue is whether a multipage document has had pages added to it after the original manuscript was written. A will or contract falls into this category. If the document is handwritten, then there may be differences in the characteristics of the writing or writing instrument.
If the document is printed, there may not be any obvious difference in the printing, but there may be differences in the paper. Even though papers may all look the same, there are chemical and physical differences between them. For example, some papers contain fillers that help improve colour and appearance. Some papers are coated to facilitate printing.
Sizing agents are added to help keep the ink from penetrating the paper, chemical tests can be performed on paper to identify these additives, but they are mostly destructive. They, therefore, cannot be done on the questioned documents.
Non-destructive physical examination may also be done on paper. For example, even though different papers may be nominally 8.5 X 11 inches, there may be slight but consistent differences from paper to paper that careful measurements can reveal. Likewise, the thickness of papers may be slightly different. Although these differences are in the thousandths of inches, measurement must be done with a special paper micrometre.
The UV rays are very helpful to differentiate the different types of paper. There may be a difference in the fluorescence when put under UV rays. One may emit green fluorescence, and the other may appear reddish.
The following methods help in the process of ink examination.
- INFRARED SPECTROSCOPY– Fourier Transform Infrared spectroscopy (FTIR) helps in the ink examination using IR radiation of the Electromagnetic spectrum. When falling on the document containing ink, these radiations vibrate the electrons, which release energy. It helps in knowing the functional group of the ink by the peaks obtained from the graphs of radiated energy.
- UV-VISIBLE SPECTROSCOPY– when the radiations falling under the regions of UV-Visible strikes on the ink, the electrons of the ink get excited and reach a higher energy shell. The de-excitation of the electrons emits light of a longer wavelength. The fluorescence helps us in determining the ink composition.
- VISUAL SPECTRAL COMPARATOR– It is a tool that helps examine and analyze the questioned document. It is an imaging device that allows an expert to analyze ink, visualize the hidden security features, and detection of alteration. This instrument can view and record the response of documents or ink when exposed to light of different wavelengths.
- CHROMATOGRAPHY– It is a destructive technique that is used for the analysis and comparison of ink when no other test is useful for detection. Thin Layer Chromatography or High-pressure Thin Layer Chromatography is preferred. Spotting ink on the TLC plates and keeping it in a chamber containing solvent system separate out the different ink components.
Age of Writing
The ink and paper analysis helps us determine the estimated age of the document, which sometimes becomes very important. We can get the subsequent facts: –
- The age of the paper may be roughly estimated from its condition, watermarks, composition of the fibre, size, material used, etc.
- By estimating the age of the ink, we can estimate the age of the document. There will be a change in the colour of the ink due to oxidation. Chloride or sulfate diffusion from the ink line gives an approx. age of writing.
- The use of a particular pen makes a point to the age of writing.
- Distinct marks on revenue stamp and change of seal from time to time help us determine the approx. age of the document.