Examination and comparison of fountain pen inks are very important in forensic questioned documents examination in developing countries where the chances of fraud are greater in cases of cheques, marriage papers, entry of birth and death, etc. In this study, fountain pen inks of blue, black, green, and red colours that are commercially used in Pakistan have been discriminated by UV-Vis spectroscopy, TLC, and FTIR spectroscopy. We have calculated and compared the results in terms of discriminating power. UV/Visible Spectroscopy of fountain pen inks of different brands showed different composition despite their similar colours. TLC was effectively used to differentiate between the colored components of inks. FTIR results showed that each brand could be distinguished by studying the pattern of their absorption spectra that appeared due to the presence of different functional groups. On the basis of combined results of UV-VIS, TLC, and FTIR, the DP was found from 0.73-0.8 for blue, 0.80-1.0 for black, 0.5-1.0 for green, and 1.0 for red colored fountain pen inks. Overall, this study demonstrated the elevated worth of analysis of fountain pen inks commercially used in Pakistan as the study for fountain pen inks, while not very common, remains an interesting target study.
The fountain pen is being extensively used as an instrument of writing for more than 10 decades. In our public existence, it is regularly utilized to sign official manuscripts. In forensic questioned document examination, criminal cases concerning inaccurate or rewritten documents come across for examination and, therefore, the way for detection and dating of fountain pen ink has a vital role in that field [
Ink applied to the surface of paper contain similar main components of dye and, however, may further be differentiated by differences in their IR spectrum [
In order to differentiate between the inks, TLC has become a typical method for routine analysis [
More recently, for statistical representation, multivariate analysis has become popular among the researchers for forensic discrimination of samples of paper [
The purpose of this study is to prepare ink examination datum for fountain pen inks used in Pakistan as the data for fountain pen inks used in Pakistan is not available. Therefore, the study of fountain pen inks is novel. There are methods for the nondestructive examination of inks including Video Spectral Comparator (VSC), Raman Spectroscopy [
Total 18 ink bottles/pots of fountain pen inks (blue fountain pen inks of six different brands, black fountain pen inks of six different brands, green fountain pen inks of four different brands, and red fountain pen inks of two different brands as shown in Table
Sample of fountain pen inks of different colors and brands.
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1 | Dollar (Blue) | BL1 | Sheaffer (Black) | BK1 | Pelikan (Turquoise) | GN1 | Dollar(Red) | RD1 |
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2 | Decent (Blue) | BL2 | Parker Quink (Black) | BK2 | Pelikan (Green) | GN2 | Nafees(Red) | RD2 |
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3 | Pelikan (Blue) | BL3 | Pelikan (Black) | BK3 | Parker Quink (Green) | GN3 | - | - |
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4 | Deer(Blue) | BL4 | Dollar (Black) | BK4 | Dollar (Green) | GN4 | - | - |
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5 | Piano(Blue) | BL5 | Deer(Black) | BK5 | - | - | - | - |
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6 | Nafees(Blue) | BL6 | Nafees(Black) | BK6 | - | - | - | - |
In parallel, fountain pen ink samples were also used directly with dilution with water wherever required to assure the effect of sampling on analytical results.
The discriminating power of techniques was calculated according to the formula available in the literature [
Samples for UV-Visible spectroscopy were prepared by transferring 10
Each extracted ink sample was spotted on TLC plate (Silica gel 60 F254(20 x 20 cm), Merck, Germany) using a capillary tube of 0.5 mm. Different solvent systems were tried/checked for the experiment, e.g., Ethyl Acetate : Ethanol (70 : 30), Ethyl Acetate : Ethanol : Ammonia (70 : 30 : 0.5), Butanol : Ammonia : Water (60 : 15 : 25), and Butanol : Acetic Acid : Water (60 : 15 : 25). Best results were obtained using Butanol, Acetic Acid, and Water (60 : 15 : 25); therefore, all samples of blue (BL1-BL6), black (BK1-BK6), green (GN1-GN4), and red (RD1-RD2) inks were eluted using Butanol : Acetic Acid and Water (60 : 15 : 25) as solvent system. The retention factor (Rf) and color tones of the separated bands were determined. The procedure was repeated five times for each sample to obtain better reproducibility.
IR analysis was performed using Agilent Cary 630 FTIR instrument using Sample interface Diamond ATR with 32 samples as well as background scans and 2 cm−1 spectral resolution; the spectral range used was 4,000 cm−1 - 650 cm−1 using Agilent MicroLab PC software, Automated IQ/OQ, 21 CFR Part 11 compliant, Resolutions Pro for advanced data analysis.
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All graphs are normalized using Origin Software (version 6.0).
UV-Visible spectroscopy is a principal tool to investigate coloring agents in inks [
Different absorption bands for blue, black, green and red fountain pen inks using UV/Visible spectroscopy.
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280 | 280 | - | 280 | - | 280 | - | 235 | - | - | - | 235 | 255 | - | 255 | 235 | - | 250 |
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315 | 315 | 315 | 315 | 315 | 315 | 335 | 315 | 320 | 310 | 305 | 302 | - | - | - | 265 | - | 270 |
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385 | - | 385 | 385 | - | 385 | 415 | - | 415 | - | - | - | 310 | 305 | 310 | - | 330 | 335 |
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595 | 605 | 595 | 595 | 601 | 585 | - | - | - | 500 | 510 | 507 | 410 | 385 | 410 | 430 | 505 | 505 |
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- | - | - | - | - | - | 575 | 590 | 570 | 610 | 595 | 605 | 630 | 640 | 630 | 640 | - | - |
Normalized UV/Visible absorption spectra for blue fountain pen inks. 1, 2, 3, 4, 5, and 6 represent samples no. BL1, BL2, BL3, BL4, BL5, and BL6, respectively.
Among black fountain pen inks (Figure
Normalized UV/Visible absorption spectra for black fountain pen inks. 1, 2, 3, 4, 5, and 6 represent samples no. BK1, BK2, BK3, BK4, BK5, and BK6, respectively.
In Figure
Normalized UV/Visible absorption spectra for green fountain pen inks. 1, 2, 3, and 4 represent samples GN1, GN2, GN3, and GN4, respectively.
Similarly, comparison of UV-Vis spectra (Figure
Normalized UV/Visible absorption spectra for red fountain pen inks 1 and 2 represent RD1 and RD2, respectively.
Five replicas of all samples were run to assess the repeatability of the measurements. Similar results were obtained when compared with the samples of inks extracted from the paper in water. In such experiments, the relative standard deviation (RSD) observed was 4%. For interpreting the results, understanding of discriminating power (DP) of an examination is of enormous help to forensic analysts, although a very limited information is present in literature for the discriminating power [
Discriminating power for blue, black, green and red inks using UV/Visible spectroscopy.
Color of Fountain Pen ink | n= total no. of samples | Total no. of pairs= n(n-1)/2 | Discriminating pairs (total no.) | Non Discriminating pairs (total no.) | D.P=no. of discriminating pairs/ Total no. of pairs |
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Blue | 6 | 6 | BL1,BL2;BL1,BL3;BL1,BL5;BL2,BL3;BL2,BL4;BL2,BL5; BL2,BL6;BL3,BL4;BL3,BL6;BL4,BL5;BL5,BL6 (11) | BL1,BL4;BL1,BL6;BL3,BL5; BL4,BL6 (4) | 11/15=0.73 |
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Black | 6 | 6 | BK1,BK2;BK1,BK4;BK1,BK5;BK1,BK6;BK2,BK3;BK2,BK4; BK2,BK5;BK2,BK6;BK3,BK4;BK3,BK5;BK3,BK6; BK4, BK6; BK5,BK6 (13) | BK1,BK3;BK4,BK5 (2) | 13/15=0.87 |
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Green | 4 | 4 | GN1,GN2;GN1,GN4;GN2,GN3;GN2,GN4;GN3,GN4 (5) | GN1,GN3 (1) | 5/6=0.83 |
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Red | 2 | 2 | RD1,RD2 (1) | None (0) | 1/1=1 |
TLC is the most extensively used technique for routine analysis because of its simplicity and low cost [
Chromatogram of blue ink samples BL1-BL6 (Figure
TLC plate developed for (a) blue fountain pen inks, (b) black fountain pen inks, (c) green fountain pen inks, and (d) red fountain pen inks.
Among the samples of black fountain pen inks, samples BK1-BK4 show three bands of different colors, whilst samples BK5 and BK6 show four bands and two bands, respectively. From the results mentioned in Table
For TLC chromatogram of green fountain pen ink samples, the results indicate that samples GN1 and GN2 show three bands of different colors with different Rf values, and sample GN3 shows five bands while sample GN4 shows only two bands of different colors.
Similarly, red fountain pen inks, i.e., samples RD1 and RD2 show a different number of bands of different colors with different Rf values. Sample RD2 shows three bands while sample RD1 shows four bands of different colors.
On the basis of qualitative information using TLC, discriminating power calculated for this study (as mentioned in Table
Discriminating power of blue, black, green and red fountain pen inks using TLC.
Color of Fountain Pen ink | n= total no. of samples | Total no. of pairs= n(n-1)/2 | Discriminating pairs (total no.) | Non Discriminating pairs (total no.) | D.P=no. of discriminating pairs/ Total no. of pairs |
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Blue | 6 | 6 | BL1,BL2; BL1,BL4; BL1,BL6;BL2,BL3;BL2,BL4;BL2,BL5;BL2,BL6;BL3,BL4; BL3,BL6;BL4,BL5;BL4,BL6;BL5,BL6 (12) | BL1, BL3; BL1,BL5; BL3,BL5 (3) | 12/15=0.80 |
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Black | 6 | 6 | BK1,BK2;BK1,BK3;BK1,BK4; BK1,BK5;BK1,BK6;BK2,BK3;BK2,BK4;BK2,BK5;BK2, BK6;BK3,BK4;BK3,BK5;BK3,BK6;BK4,BK5;BK4,BK6; BK5,BK6 (15) | None (0) | 15/15=1 |
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Green | 4 | 4 | GN1,GN2;GN1,GN3;GN1,GN4;GN2,GN3;GN2,GN4;GN3, GN4 (6) | None (0) | 6/6=1 |
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Red | 2 | 2 | RD1,RD2 (1) | None (0) | 1/1=1 |
Calculated Rf values for blue, black, green and red inks using TLC.
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BL1 | 0.03 | 0.19 | 0.34 | BK1 | 0.08 | - | 0.15 | - | 0.30 | - | - | GN1 | 0.19 | 0.37 | - | - | 0.4 | - | RD1 | 0.09 | 0.2 | 0.67 | 0.71 |
BL2 | 0.12 | 0.19 | 0.34 | BK2 | - | 0.11 | 0.28 | 0.19 | - | - | - | GN2 | - | - | 0.30 | 0.25 | 0.07 | - | RD2 | 0.11 | 0.42 | 0.67 | - |
BL3 | 0.03 | 0.20 | 0.34 | BK3 | 0.03 | - | 0.47 | - | 0.33 | - | - | GN3 | 0.19 | 0.37 | - | 0.30 | 0.37 | 0.26 | - | - | - | - | - |
BL4 | 0.05 | 0.20 | 0.34 | BK4 | 0.08 | - | - | 0.64 | - | 0.39 | - | GN4 | - | - | 0.30 | 0.05 | - | - | - | - | - | - | - |
BL5 | 0.03 | 0.20 | 0.34 | BK5 | 0.08 | - | - | 0.67 | - | 0.42 | 0.22 | - | - | - | - | - | - | - | - | - | - | - | - |
BL6 | 0.03 | 0.14 | 0.34 | BK6 | - | - | - | 0.69 | - | 0.42 | - | - | - | - | - | - | - | - | - | - | - | - | - |
The discrimination of inks by FTIR spectra is achieved due to the difference in the number of peaks, peak positions, and peaks intensities with respect to each other [
Absorption peaks for blue fountain pen inks have been marked by comparing their positions with the literature [
Normalized FTIR absorption spectra for blue fountain pen ink. 1, 2, 3, 4, 5, and 6 represent samples no. BL1, BL2, BL3, BL4, BL5, and BL6, respectively.
Similarly, the assignment of peaks for black, green, and red fountain pen inks has been made by comparing their IR data with the literature. For black fountain pen inks (Figure
Normalized FTIR absorption spectra for black fountain pen inks. 1, 2, 3, 4, 5, and 6 represent samples no. BK1, BK2, BK3, BK4, BK5, and BK6, respectively.
Normalized FTIR absorption spectra for green fountain pen inks. 1, 2, 3, and 4 represent samples no. GN1, GN2, GN3, and GN4, respectively.
Normalized FTIR absorption spectra for red fountain pen inks. 1 and 2 represent samples no. RD1 and RD2, respectively.
On the basis of qualitative information, discriminating power for this study by using FTIR has been found as 0.73 for blue, 0.80 for black, 0.5 for green, and 1.0 for red colored fountain pen inks (Table
Discriminating power of blue, black, green and red fountain pen inks using FTIR.
Color of Fountain Pen ink | n= total no. of samples | Total no. of pairs= n(n-1)/2 | Discriminating pairs (total no.) | Non Discriminating pairs (total no.) | D.P=no. of discriminating pairs/ Total no. of pairs |
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Blue | 6 | 6 | BL1,BL2;BL1,BL3;BL1,BL6;BL2, BL3;BL2,BL4;BL2,BL5;BL2,BL6;BL3,BL4; BL3,BL5;BL4,BL6; BL5,BL6 (11) | BL1,BL4; BL1,BL5; BL3, BL6; BL4,BL5 (4) | 11/15=0.73 |
Black | 6 | 6 | BK1,BK2;BK1,BK3;BK1,BK4;BK1,BK5; BK1,BK6;BK2,BK3;BK2,BK4; BK2,BK5;BK2,BK6;BK3,BK4;BK3,BK5; BK3,BK6;BK5,BK6 (12) | BK4,BK5; BK4,BK6; BK5,BK6 (3) | 12/15=0.80 |
Green | 4 | 4 | GN1,GN3; GN2,GN3;GN3,GN4 (3) | GN1,GN2; GN1,GN4; GN2,GN4; (3) | 3/6=0.5 |
Red | 2 | 2 | RD1,RD2 (1) | None (0) | 1/1=1 |
The data for forensic discrimination potential of different techniques or for the succession of techniques used for fountain pen inks are not extensively accessible as most of the data available is for ballpoint pen inks. In the present study, the discriminating power (DP) for fountain pen ink was found to be 0.73, 0.87, 0.83, and 1.0 for blue, black, green, and red colored inks, respectively, using UV/Visible Spectroscopy. DP for fountain pen inks was found to be 0.80, 1.0, 1.0, and 1.0 for blue, black, green, and red colored inks, respectively, using Thin Layer Chromatography. DP for fountain pen inks was found to be 0.73, 0.80, 0.5, and 1.0 for blue, black, green, and red colored inks, respectively, using Fourier Transform Infrared Spectroscopy. The discriminating powers, i.e., 0.73 and 0.5, calculated from FTIR analysis of blue and green inks, respectively, show that FTIR for blue and green fountain pen inks is not as good as UV/Visible Spectroscopy and TLC. One pair of blue fountain pen inks BL1 and BL4 was indiscriminating by UV/Visible and FTIR spectroscopy, but by applying TLC it was discriminated. TLC and UV/Visible have been found to be more efficient and reliable techniques for analysis of fountain pen inks as compared to FTIR technique. By using TLC, BL1, BL3, and BL5 cannot be discriminated. The UV-Visible spectra of these 3 inks show a difference in the UV. BL1 has a shoulder at about 280 nm to the peak at about 300 nm. There is no shoulder at this position on BL3 and BL5 indicating that UV/Vis spectroscopy gave a further level of discrimination after TLC. This type of logic shows how the methods complement each other. With the increase in the number of samples, the discriminating power also increases, e.g., in blue fountain pen inks (total 06 samples) DP for four nondiscriminating pairs becomes 0.73 and in case of green fountain pen inks (total 04 samples) with three nondiscriminating pair DP becomes 0.50.
Further study for determination of metal content in blue, black, green, and red fountain pen inks is recommended for their better discrimination.
Raw data files of all techniques are available and can be provided on demand.
The authors declare that they have no conflicts of interest.