Age Determination of Ink
Ink is a colored liquid that is used to write or draw on paper. The inks can be in aqueous, powder, or paste form. Inks were first discovered by the Egyptians who used to write and draw things. Another big contribution to ink discoveries and development was the Chinese. In fact, Indian ink was invented in China.
Components of Ink
Ink is basically a mixture of various components that have their individual functions. The basic components of the ink are:
1. Pigments
Pigments are the ones that give color to every ink. The pigments can be made up of either organic or inorganic compounds. It is the main component of the ink.
2. Dispersants
Dispersants are used as surfactants and polymers in the ink.
3. Resins or Polymers
Resins and polymers are helpful in improving the binding of the components in ink.
4. Humectants
Humectants are the components that help in retarding the premature drying of the ink.
5. Defoamers and Antifoaming Agents
These agents are used to prevent the production of any foam, which may interfere with the ink formation process.
6. Wetting Agents
The wetting agents are the ones that enhance the contact of the ink with the substrate.
7. pH Modifiers
pH modifiers are used to maintain the pH of the ink so that the mixing of every ink component can take place effectively. For this purpose amine derivatives are added to the inks.
8. Biocides and Bacteriostats
These chemicals are used to prevent or kill any bacterial growth, which can destroy or decompose the ink.
Types of Inks
There are various types of inks present for writing or drawing. Bt the major types of inks are:
1. Indian Ink
Indian ink is the suspension of carbon in water. The carbon used is in the form of lampblack. It is also known as Chinese ink because it was invented in China. However, the ingredients used in the ink were traded from India, hence the name is Indian ink.
2. Ball Pen Ink
The ink is prepared by suspending different types of dyes in oil or glycol.
3. Iron Tannate Ink
This ink is formed by mixing tannic acid and gallic acid obtained from wood, with iron salts. The mixture obtained is a colorless solution that turns black with the passage of time. Acids and phenols are added to the mixture which provides stability to the ink. It is a permanent ink, therefore is used worldwide for important documents.
4. Dyestuff Ink
These inks are prepared from nigrosine dyes which are available in different types of shades and colors. These inks are washable and fade away with time as they are not permanent.
5. Logwood Ink
It is an ink that is extracted from logwood with potassium dichromate. It is a permanent ink.
6. Indelible Ink
It is also known as election ink as it is used in elections to mark the voters. It is a semi-permanent ink that is made up of different concentrations of silver nitrate.
7. Alkaline Ink
These inks are obtained from the dyes and complexes of copper or vanadium. They are permanent and quick-drying inks.
8. Stamp-Pad Ink
The stamp-pad ink is prepared by mixing dyes, glucose, and glycerol.
9. Typewriter Ink
The ink is made up of mixing dyes and castor oil.
10. Printer’s Ink
This ink is used in all types of printers and is prepared by mixing carbon, adhesives, and drying oils.
Ink Analysis
Ink is a component that makes a drawing or writing visible which means it is important to examine the ink which can elucidate information about the erasures, obliterations, or additions in the questioned document. Another important information ink analysis can provide is the age of the document.
There are several types of analytical methods that are used to analyze the ink to examine different properties of the ink that include:
1. Visual Examination of Ink
This examination is usually done by illuminating the document with an angle-poise table lamp. It reveals any types of erasures or obliteration in the document.
2. Chemical Analysis
The chemical tests are done to elucidate the acidic or alkaline nature of the ink.
3. Spectrographic and Spectroscopic Methods
These instrumental methods are used to determine the type of ink used in the document.
4. Chromatographic Methods
These methods are used to separate the components of the ink and analyze them.
5. Electrophoresis
Electrophoresis is used to separate the dyestuffs from the ink.
6. Video Spectral Comparator (VSC)
VSC uses the UV, Visible and Infrared rays that fall on the questioned writing, helping in studying the ink.
Ink Dating
The age of ink is a piece of important information that helps determine a document’s age. There have been certain methods developed for dating ink but none of them proved to estimate the exact age of ink. The characteristics of ink which can be useful in ink dating are color changes, smudging effects, changes in the chemicals of ink, etc.
1. Visual Examination
The color of the ink can indicate the age of the ink. However, only blue-black ink shows this change over the course of time yet the fadeness of inks can be considered for other inks. The changes in the appearance of the ink depends on the temperature, humidity, air, exposure to sunlight, the paper used, the site where the document was kept, etc.
2. Smudging
When the ink is mixed with water, the time taken by the ink to dissolve in water can indicate the age of the ink. It has been observed that fresh inks are smudged immediately in water whereas aged inks take more time to dissolve because, with the course of time, the inks fade and become insoluble.
3. Diffusion of ink
Usually, inks contain chloride or sulfate ions, which are present in the acids used in the ink production process. These ions, with the passage of time, are diffused in the paper. The diffusion can be tested by treating the paper containing ink, with lead acetate or silver nitrate, which will precipitate the lead sulfate or silver chloride respectively.
This can be easily observed on the paper. The intensity of the precipitation will reveal the extent of ink diffusion in the paper. This will ultimately indicate the age of the ink.
4. Chemical Tags Analysis
In the early 1970s, rare earth elements and special chemicals were added to the ink for detection and dating purposes. Thin Layer Chromatography(TLC) along with UV excitation is an effective method to identify such special chemical tags in the ink.
This test reveals the age of the ink and also helps to identify the manufacturer of the ink. With the advancement of technology, chemical tags can be analyzed using X-ray Excited Optical Fluorescence Spectrometer (XREOF) that produces highly selective line emissions. However, this method is not used in India.
Conclusion
Ink is the colorful liquid that makes the writings or drawings visible. It is composed of many constituents that make up the inks that we use to write or draw. It is an important factor considered during questioned document analysis.
Ink dating is an important examination that helps in estimating the age of the paper used as well as the age of the questioned document.
There have been cases where the courts have asked for expert opinions on the age of inks, therefore it is an important aspect of forensic document examination.
There are various methods available for dating ink but none of them are able to estimate the exact age of the ink, which is one of the limitations of the analytical methods. Another problem is that these methods are not easy to conduct and consume a lot of time.
Therefore, new techniques are required to be invented and new developments should be made in the existing techniques so that more effective and reliable results can be obtained.
