Visualizing latent fingerprints on color-printed papers using ultraviolet fluorescence

Laser detection of latent fingerprints on a white paper has been performed, previously. Ultraviolet fluorescence from various kinds of printer toner and ink used for home printers were measured to study fluorescence imaging of fingerprints on a color-printed white paper. The experimental system consisted of a nanosecond pulsed tunable laser and a cooled CCD camera. Excitation wavelengths are 230 and 280 nm. Fourteen printers consisting of three color laser printers, three color inkjet printers, five monochrome laser printers, two monochrome copy machines, and a color copy machine were tested. Toner and ink of most printers exhibited fluorescence in the region from 360 to 550 nm. In most cases, clear fluorescence images were obtained by time-resolved imaging with a band-pass filter and 280-nm excitation. However for toners from laser color printers that showed strong fluorescence, better results were obtained with 230-nm excitation. Latent fingerprints on a photograph page and a black-character page of a newspaper were also imaged.     

The detection of multiply charged dyes using matrix-assisted laser desorption/ionization mass spectrometry for the forensic examination of pen ink dyes directly from paper

Abstract:  Laser desorption mass spectrometry (LDMS) is emerging as a technique for questioned document examination. Its use is limited to detecting ink dyes that are neutral or singly charged. Several inks contain dyes that are multiply charged and LDMS cannot be employed for their identification. We have successfully detected >20 polyionic dyes that can be used in the manufacture of inks using matrix-assisted laser desorption/ionization (MALDI) MS, directly from paper, with the matrix, 2-(4-hydroxyphenylazo)benzoic acid (HABA), and the additive, diammonium hydrogen citrate (DAHC). For example, Acid Violet 49, a charged dye containing one positively-charged site and two negatively charged sulfonate groups, cannot be detected by LDMS, but forms intact, singly charged ions in the MALDI MS experiment. The method described is also useful for identifying multiply charged dye mixtures that are used in modern pen inks.     

利用IDMH-Z780系统对碳素钢笔水书写字迹与印章印文交叉时序的无损检验研究

目的研究常见的碳素钢笔水书写笔迹与不同印章印文交叉时序的相关性。方法利用IDMH-Z780系统对制成的实验样本进行微观观察,并对三维数学模型图进行特征分析。结果先墨后朱,交叉部位字迹边缘状态完整,等高线宽度、流向未见明显变化;先朱后墨,书写笔迹色料分布发生数字图形曲面变化。结论用IDMH-Z780系统可以观察分析朱墨交叉部位的微观特征和无损检验研究。     

Preliminary Study on Determining the Sequence of Intersecting Lines by Fluorescence Technique

The determination of the sequence of intersecting lines is an important part of questioned document examinations. A fluorescence technique was used to determine the sequence of heterogeneous intersecting lines produced using inkpad ink, stamp‐pad ink, ballpoint pens, gel pens, fountain pens, colorants of carbon paper, photocopiers, laser printers, and inkjet printers. A SteREO Discovery.V20 equipped with the ZEN Blue Lite software was chosen to perform the tests.As the results obtained from the study were positive under most conditions, the fluorescence technique was found to be very successful in determining the sequence of intersecting lines from ballpoint pen, gel pen, fountain pen, photocopier, laser and inkjet printers, and inkpad inks. The method was also successful in determining the sequence of intersecting lines from ballpoint pen, photocopier, laser printer, and stamp‐pad inks under most conditions. The technique was not successful in determining the order of crossing lines blending together.     

GC-HPLC法考察圆珠笔字迹油墨厚度对溶剂挥发速率的影响

目的考察圆珠笔字迹油墨厚度对溶剂挥发速率的影响。方法采用GC/HPLC联用技术对不同时间、不同字迹油墨厚度在同种纸张上的圆珠笔油墨字迹中的溶剂、染料成分的定量分析。结果字迹油墨较厚的苯甲醇、苯氧基乙醇的含量随时间的变化比字迹油墨较薄的慢。结论字迹油墨的厚度对溶剂的挥发速率影响较大。     

浅析影响碳素墨水显现胶带指纹的若干因素

为提高胶带粘面指纹的显现质量,便于后期针对该指纹的检验鉴定,通过对胶带粘面指纹显现过程中的各个环节进行测试、对比,可以寻找出一些影响显现效果的因素。经过实验发现,在胶带剥离阶段及对胶带的浸泡、显现阶段,各种不同的实验材质、环境、手法均会对指纹显现效果产生影响。     

Age determination of ballpoint pen ink by thermal desorption and gas chromatography-mass spectrometry

Two main approaches can be used for determining the age of an ink: indirect dating and direct dating. Indirect dating is based on the chemical analysis of an ink followed by comparison with known samples in a reference collection. The collection should contain information about the inks including the market introduction dates. This approach may allow for an anachronism to be detected. The second concept is based on measuring ink components that change with age. The analysis of solvents in ballpoint inks may be a useful parameter for determining the age of ink on paper. In a previous study, the authors demonstrated that thermal desorption of ink directly from paper, followed by chemical analysis using gas chromatography-mass spectrometry (GC-MS), is a promising procedure for characterizing ink-binder resins and solvents. Preliminary tests showed that monitoring the evaporation of ink solvent from ink on paper is not a suitable method for ink dating. Thermal analysis of ink on paper in two steps revealed that fresh ink releases a relative amount of solvent at a certain low temperature in a defined period of time, which decreases as the ink ages. As a consequence, this relative amount of solvent released at a certain low temperature, and its decrease with time, can be used to estimate ink age. This age-dependent parameter was studied in 85 different inks ranging in age from 1 week to 1.5 years. It was found that some inks showed a significant decrease of this parameter up to an age of several months, and that the aging process can be monitored within this period. For other inks, however, the age-dependent parameter decreases relatively fast, e.g., within a few days, to a constant level, which can be too fast for casework. Based on these results, a general procedure for assessing the age of ballpoint pen inks on paper was developed.     

Identification of colorants in pigmented pen inks by laser desorption mass spectrometry

Pigments are rapidly replacing dyes as colorants in pen and printer inks, due to their superior colors and stability. Unfortunately, tools commonly used in questioned document examination for analyzing pen inks, such as TLC, cannot be used for the analysis of insoluble pigments on paper. Laser desorption mass spectrometry is demonstrated here as a tool for analyzing pigment-based pen inks. A pulsed nitrogen laser can be focused onto a pen stroke from a pigmented ink pen on paper, and positive and negative ions representative of the pigment can be generated for subsequent mass spectrometric analysis. Targeted pens for this work were a set of Uni-ball 207 pigmented ink pens containing blue, light blue, orange, green, violet, red, pink, and black inks. Copper phthalocyanine was identified as the pigment used to make both blue inks. A mixture of halogenated copper phthalocyanines were identified in the green ink. Unexpectedly, the pink ink was found to contain a red pigment, Pigment Red 12, treated with a mixture of water-soluble dyes. Each sample yielded ions representative of the pigments present.     

Identification and dating of the fountain pen ink entries on documents by ion-pairing high-performance liquid chromatography

A novel approach for the identification and dating of the fountain pen ink entries on paper has been established by ion-pairing high-performance liquid chromatography (IP-HPLC). Twelve black and six red fountain inks have been collected, and their ink entries have been prepared by drawing lines on paper. The chromatographic conditions for separation of their dye components after extraction with solvents were optimized. Under the optimized conditions, the 18 fountain pen inks were differentiated individually by comparing the number of detectable main or minor dye components, and the relative peak intensities of each component. The ink entries were artificially and naturally aged, and the analysis results showed that the ink dye components were significantly decomposed when exposed to UV or fluorescent light compare to those of inks stored under natural condition. The changes of the relative peak height for the dye components were linearly related to the aging time, especially under natural aging conditions. The degradation characteristics of the dye components under different aging conditions provide scientific evidences for dating of the suspicious fountain pen ink entries on document.     

Bruise dating using deep learning

The bruise dating can have important medicolegal implications in family violence and violence against women cases. However, studies show that the medical specialist has 50% accuracy in classifying a bruise by age, mainly due to the variability of the images and the color of the bruise. This research proposes a model, based on deep convolutional neural networks, for bruise dating using only images, by age ranges, ranging from 0–2 days to 17–30 days, and images of healthy skin. A 2140 experimental bruise photograph dataset was constructed, for which a data capture protocol and a preprocessing procedure are proposed. Similarly, 20 classification models were trained with the Inception V3, Resnet50, MobileNet, and MnasNet architectures, where combinations of learning transfer, cross‐validation, and data augmentation were used. Numerical experiments show that classification models based on MnasNet have better results, reaching 97.00% precision and sensitivity, and 99.50% specificity, exceeding 40% precision reported in the literature. Also, it was observed that the precision of the model decreases with the age of the bruise.