An evaluation of matching unknown writing inks with the United States International Ink Library

Utilizing a database of standards for forensic casework is a valuable resource. Undoubtedly, as more standards (and corresponding information about the specimens) are collected, there is a greater certainty of identification when a questioned and a known item cannot be distinguished after a series of analyses. The United States Secret Service and the Internal Revenue Service National Forensic Laboratory jointly maintain the largest known forensic collection of writing inks in the world, which is comprised of over 8500 ink standards collected worldwide, dating back to the 1920s. This study was conducted to evaluate the reliability of matching arbitrarily purchased pens with known inks from a database. One hundred pens were randomly obtained from a variety of sources and their respective ink compositions were compared with standards. Eighty-five of the inks were determined to be suitable for comparison utilizing optical examinations and thin-layer chromatography. Three of the inks did not match any of the specimens on record; one of these inks was similar to an ink from an identical brand of pen that was in the database, but had a modified formulation.     

A simple microthermal desorption device

A new method for thermal desorption of small samples is presented. The method uses a solid phase microextraction (SPME) holder with the fiber removed. The sample-for example, an ink sample on paper-is simply placed inside the needle of the holder, where normally an SPME fiber is positioned. The thermal desorption is then performed on any kind of gas chromatograph in a manner similar to that for SPME analysis. The needle of the SPME holder penetrates the injector septum; the temperature of the thermal desorption is simply the temperature of the injector. No solvents or liquid nitrogen cooling are used. The paper sample is kept inside the holder needle during the analysis. After the analysis is completed, the sample is removed from the needle by pushing forward the steel wire inside the needle in the way normally used to perform sampling with the SPME fiber. The desorbed compounds were analyzed by gas chromatography with a flame ionization detector or by gas chromatography-mass spectrometry. The optimum temperature for desorption of ink samples on paper was 200 degrees C. The influence of the paper matrix is negligible at that temperature. Laboratories lacking the commercial device for thermal desorption can use this cheap device for the analysis of, for example, writing ink, printing ink, and inkjet ink samples on paper. Other types of samples can be investigated but the size of samples suitable for analysis is limited.     

FTIR图像—单点模式法无损鉴别不同品牌激光打印机墨粉色痕

利用傅里叶红外图像系统,采用单点模式对收集到的八种品牌激光打印机墨粉色痕进行红外扫描,采集样品红外光谱,并对其中两种样品红外光谱进行二阶导数运算,得到对应的二阶导数光谱。实验表明,该方法可有效区分不同品牌激光打印机墨粉色痕,并可为其他书写材料无损检验鉴定提供借鉴。     

Comparison of feature selection and data fusion of Fourier transform infrared and Raman spectroscopy for identifying watercolor ink

The identification of different kinds of watercolor inks is an important work in the field of forensic science. Four different kinds of watercolor ink Spectroscopy data fusion strategies (Fourier Transform Infrared spectroscopy and Raman spectroscopy) combined with a non-linear classification model (Extreme Learning Machine) were used to identify the brand of watercolor inks. The study chose Competitive Adaptive Reweighted Sampling (CARS), Random Frog (RF), Variable Combination Population Analysis-Genetic Algorithm (VCPA-GA), and Variable Combination Population Analysis-Iteratively Retains Informative Variables (VCPA-IRIV) to extract characteristic variables for mid-level data fusion. The Cuckoo Search (CS) algorithm is used to optimize the extreme learning machine classification model. The results showed that the classification capacity of the mid-level fusion spectra model was more satisfactory than that of single Infrared spectroscopy or Raman spectroscopy. The CS-ELM models based on infrared spectroscopy used to recognize the watercolor ink according to brands (ZHENCAI, DELI, CHENGUANG, and STAEDTLER) obtained an accuracy of 66.67% in the test set using all spectral datasets. The accuracy of CS-ELM models based on Raman spectroscopy was 67.39%. The characteristic wavelength selection algorithms effectively improved the accuracy of the CS-ELM models. The classification accuracy of the mid-level spectroscopy fusion model combined with the VCPA-IRIV algorithm was 100%. The data fusion method increased effectively spectral information. The method could satisfactorily identify different brands of watercolor inks and support the preservation of artifacts, paintings, and forensic document examination.     

Dating of Inkpad Seals Using the Extraction Rate Method: Preliminary Findings

Inkpad seals are often placed on important documents, and determining the date when a seal was affixed can be important to assess the authenticity of a document. In this study, three different brands of inkpads and four different types of paper were used to make diachronic samples of the seals. A double‐solvent extraction method was employed to date the inkpad seals by comparing extraction rates with inks of known age. Cyclohexane was selected as a weak solvent, and chlorobenzene was selected as a strong solvent. After testing, curves were created to show the relationship between the extraction percentage of ink and the date of the seals. The experimental results showed that the extraction rate method was applicable for the relative dating of inkpad seals in some cases where the seal was placed on the document within 6 months.     

TOF‐SIMS Analysis of Red Color Inks of Writing and Printing Tools on Questioned Documents

Time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) is a well‐established surface technique that provides both elemental and molecular information from several monolayers of a sample surface while also allowing depth profiling or image mapping to be performed. Static TOF‐SIMS with improved performances has expanded the application of TOF‐SIMS to the study of a variety of organic, polymeric, biological, archaeological, and forensic materials. In forensic investigation, the use of a minimal sample for the analysis is preferable. Although the TOF‐SIMS technique is destructive, the probing beams have microsized diameters so that only small portion of the questioned sample is necessary for the analysis, leaving the rest available for other analyses. In this study, TOF‐SIMS and attenuated total reflectance Fourier transform infrared (ATR‐FTIR) were applied to the analysis of several different pen inks, red sealing inks, and printed patterns on paper. The overlapping areas of ballpoint pen writing, red seal stamping, and laser printing in a document were investigated to identify the sequence of recording. The sequence relations for various cases were determined from the TOF‐SIMS mapping image and the depth profile. TOF‐SIMS images were also used to investigate numbers or characters altered with two different red pens. TOF‐SIMS was successfully used to determine the sequence of intersecting lines and the forged numbers on the paper.     

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.