Age Determination of Paper
Paper is one of the pieces of evidence encountered in a criminal case including murder, forgery, fraud, or suicide since it is one of the common writing surfaces for any person. Therefore, its examination is important to provide accurate data after analysis.
Paper is a thin sheet made from wood pulp or other lignocellulosic materials such as cotton, rice, or wheat straw for writing, printing, and packaging purposes. It is believed that it was originated in China in the 2nd century as an alternative writing material to silk. Almost 200 years of its mechanized production resulted in significant changes in information networking all over the world.
Steps of Paper Manufacturing
The wood is cut into small wood chips which are mixed with water and finely ground to form a pulp. This step helps in cleaning and separating fibers of wood.
The raw pulp contains an appreciable amount of lignin and other discoloration, it must be bleached to produce light-colored or white papers preferred for many products. The fibers are further delignified by solubilizing additional lignin from the cellulose through chlorination and oxidation.
The bleached or unbleached pulp may be further refined to cut the fibers and roughen the surface of the fibers to enhance the formation and bonding of the fibers as they enter the paper machine.
Calendering is a process to enhance both the physical and mechanical properties of paper. Application of a coat of various types of chemicals applied to the surface of the paper makes it extra shiny for special applications, such as art papers.
The finished paper is wound on a large reel called the winder. As the reel of paper goes to the winder, it is slit into manageable size rolls.
Properties For Forensic Examination of Paper
- Weight of paper
- The color of paper and type of coloring agent used
- The thickness of paper
- Composition of the paper
- Fiber distribution in the paper
- Strength of the paper
- Type of fillers used in the paper
Age Estimation of Paper
Earlier in this article, we discussed the manufacturing process of paper, it is this process which determines its age as well.
Paper is a material containing a number of components such as fiber, coloring agents, watermarks, coating agents, loading agents, brightening agents, etc. and these properties of paper can be used to determine the age of a paper.
Usually, the age can be obtained from the manufacturer because there is always a record-keeping process followed in the manufacturing company.
But it is not possible in every case. Therefore alternative methods have been developed for estimating the age.
Usually, the properties used to determine the age of paper include the physical appearance of paper, the composition of pulp, fiber analysis, aroma, water molecules in paper, watermarking, etc.
1. Visual Examination of Paper
With the passage of time, the physical appearance of paper changes. The physical properties like color, brightness, texture or coating, and fluorescence can help in estimating the age of the paper. These properties of questioned documents can be compared with the newly manufactured paper obtained from a company.
There is a change in the color of the paper due to the passage of time. Usually, the color fades with time.
There are different types of papers depending upon their textures which are obtained due to the coating applied on the paper. The paper can be glossy, satin-finished, or matte finish paper. The coating adds glossiness, smoothness, ink absorption, etc.
The brightness of paper refers to the percentage of blue light reflected from the surface as measured at a specific wavelength of 457 nm. To make the paper brighter, manufacturers add Optical Brighteners Agents (OBAs). These chemicals absorb light in the UV region (340-370nm) of the spectrum and re-emit light in the violet/blue region (420-470 nm). The brightness of paper fades away with the passage of time.
There are fluorescent whitening agents (FWAs) that produce a fluorescence effect. To know whether FWAs are present or not, observe the paper in dark by irradiating short (250 nm) and long (350–390 nm) UV light. As time passes, the fluorescence decreases.
2. Pulp Composition
With new inventions and developments, there has always been a tendency for experiments to produce different types of papers. It has been proved in a report of ‘Global Market Insight’, that over the course of five years, there is a 30% difference in the pulp additives added or replaced and this may continue for every five years.
So, it will be helpful to determine the relative age of the paper, and if the questioned documents were prior to the change the morphological and chemical examination of the pulp may reveal the age of the paper.
3. Fiber Composition
The paper is usually made up of wood pulp which contains a lot of fibers. The morphological and chemical analysis of the fibers present in the suspected documents can reveal the age of the paper because the fibers show visual changes and variations with time.
4. Aroma of Paper
As we all know that the fresh and new pages of a book or notebook have a characteristic smell or aroma which is liked by many people. Researchers have shown that the characteristic aroma of the papers is due to the presence of volatile organic compounds present in the paper.
With the passage of time, these compounds are released from the papers or they deteriorate, due to the aroma of older documents and different from the fresh papers.
Watermark is a design produced by creating the variation in thickness of the paper during the manufacturing process. It is one of the identifying marks of the company or organization that manufactures the paper. However, the variation in thickness of the paper is also helpful in dating. There are usually two types of watermarks- coded and uncoded.
Coded watermarks have characteristic marks or codes aligned on the logos, which show the year of the production of that paper. It is one of the easy methods of dating paper.
Uncoded watermarks are logos without any codes or markings. In such pacers, the dating is done by analyzing wear marks of the watermark produced by the defects of dandy rolls.
6. Water Pores of Paper
The paper contains cellulose fibers that encloses water molecule. Due to the trapping of water molecules, the cellulose fibers possess pores of specific size. Research has shown that this pore size changes with the passage of time, which degrades and becomes larger with time by absorbing atmospheric moisture. This is helpful in determining the age of the paper.
7. Ink analysis
Researchers have proved that ink analysis can be helpful in dating the paper.
Various types of ink analysis like ink smear on the paper relative age of the ink or the use of ink tags can help in estimating the age of paper. The presence of ink on the paper can reveal the absorptivity of paper which is an important factor in dating paper.
Paper is the most common source of any document. It has the contents in the form of handwritten form or typewritten form. It has various peculiar characteristics which are very useful from the perspective of forensic analysis of documents. One of the important pieces of information that a document can reveal is the age of the document. By dating the paper, the age of the document can be revealed.
There have been many methods developed for the purpose of dating papers, but all of them have some drawbacks. Therefore more robust methods are needed to combat the limitations of the analysis for age estimation of documents.