Gel-pen inks

Dating of inks is difficult and frequently not very reliable. GCMS has been used to identify solvents and volatiles in gel pen ink up to 6 months old, and there are some specialized mass spectrometry studies on particular materials—for example, gentian violet, 26.34, slowly loses methyl groups over time. The only truly reliable determination is to demonstrate that an ink only became commercially available after the date on which the document is purported to be written. 

The elemental composition is useful for characterisation of inorganic pigments and organic dyes. However, a database is needed for their identification. In all ballpoint pen inks, sulfur, copper, silicon and phosphorus are present in the elemental composition. Some samples also contain zinc, chlorine, bromine and calcium. In black inks, chromium and lead are additionally found. Samples differ with respect to the elemental composition quantitatively rather than the qualitatively. A greater variability in elemental content is observed for gel inks. 

Another group of mk delivery devices consists of those which operate via capillary action. Fiber-tipped pens, also called "felt tips" deliver inks with solvent bases that are aqueous, glycol based, or xylene based. Tlie inks are generally less viscous than ballpoint inks. Recently introduced gel pens are increasing in popularity and, as the name implies, deliver colorants via a gel rather than a comparatively thin solution. Colorants are primarily pigments, and once dry, the inks are virtually insoluble. As a result, forensic analyses are more complex, but still feasible, as is discussed later in the chapter. 

Black gel inks from 29 pens and 17 companies were differentiated by TLC on Merck silica gel 60 layers developed with ethyl acetate-ethanol-water (75 35 30) mobile phase. A VSC 2000 HR was used to examine and document the TLC plates in visible, LfV, and near IR reflectance (IRR) modes. Written gel ink lines on filter paper were sampled by extracting 1.3 mm punch holes with 20 pi of ethanol-water (1 1). Spot tests and capillary column GC/MS were also used for ink analyses in this study.A flowchart was developed allowing systematic determination of a questioned ink. 

We usually stretch a sheet of transparent paper across the layer with two paper clips, examine in transmitted light and trace the spots in ink with a soft pen. Even very feeble, pale yellow spots can be detected on the white silica gel layer with a little practice. It is often easier to inspect the layer in transmitted UV light (light source layer... 

If a colorant can be solubilized, it can be evaluated by means of TLC. This technique is commonly employed for ink analysis but not for paints. A 1982 report described the use of TLC in isolating pigments in house paint, followed by IR identification of separated spots, but this is one of few such reports and TLC is infrequently used this way. However, for inks, TLC is an accepted and widely used discriminatory tool that is applicable to a variety of pens and toners. The ASTM guide for ink analysis (E 1422) recommends pyridine as a solvent for glycol-based ballpoint inks and an ethanol-water (1 1) combination for nonballpoint inks. The stationary phase is typically silica gel and the solvent S) tems are based on ethanol and water. There are still many inks in which the colorants can be separated with nothing more than water and filter paper. Dyes in textiles can be similarly examined, a topic discussed in Chapter 14. 

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