The Analysis of Ball-Point lnks for Forensic Purposes C. H. Breedlove Montgomery Community College, Rockville, MD 20850 Ball-point pens and the variety of colored inks that flow from them have been a ubiquitous part of our society for about 50 years. They are the most common of all our writing instruments. The examination of these kinds of inks sometimes becomes important in a legal case, and in a typical crime laboratory, the analysis of the ink used on questioned documents such as contracts, wills, checks, tax returns, threat notes, etc., becomes the responsibility of the forensic chemist. I t is the purpose of this paper to descrihe the typical steps used in the analysis of ball-point ink. The ink that flows from a ball-point pen is not a pure substance, but a complex mixture of many different cbemicals. There are now in existence literally thousands of different formulations for inks, depending on the type of writing instrument to be used, the color desired, and any other special t characteristics that the manufacturer mav wish to i m ~ a rto the particular ink. It is convenient to categorize three major classes of chemicals used in ball-point inks': 1. Color: Modern hall-ooint ink formulations eet their colors from
the palette of the sinthetic dye chemist anh include such brilliantly colored species as methyl violet, victoria blue, and luxol iast orange, nigrosine, copper phthalocyanine,and other organometallic dyes. Dyes and pigments compose about 25%of the mass ofa typical ink. 2. Solvents,or"\~ehicles"astheyarecalled in the ink industryniakc u~about505 oithemassofan ink. Modern ball-noint inksOlokt1950)use a mixture of glycols as the solvent, etbyiene glycol being a common one. Prior to 1950. oils such as linseed or mineral ail were used as the vehicle. The vehicle diusolveu or suspends the dyes/piglnentsand promotes the smooth flow of the i n k over the surfaceof the rotating ball.The vehicle drirs quirkly by evaporation, although measurable amounts can still he detected by gas chromatography for as long as 2 months after the ink has been applied to a doc~ment.~ 3. The remaining 25% of the ink is due to resins, both naturally occurring and synthetic polymeric materials. The primary purnose of the resins is to imoart a favorable viseositv to the ink. Ball-point ink in hulk ir a thick, almost honeylike materiel. A major objective ia to have it flow during the time of writing vnlg. Relatively small amounts of other material often found in ball-point ihk include surfactants (as in detergents) to improve the wettability, corrosion inhibitors to protect the metal parts of the pen, and acidic materials to help lubricate the ball and neutralize alkaline dyes. One manufacturer (Fisher) uses nitrogen as a propellant gas to force the extremely thick ink out of its pressurized cartridge and onto the writing surface. Since this design can write in a vacuum or in the absence of gravity, i t was chosen for the astronauts' use by NASA. Under what circumstances might it become important to
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Brunelle, R. L.; Reed. R. W. Forensic Examination of Ink and Paper; Thomas: Springfield. IL. 1984. Stewart, Larry F. J. For. Sci. 1985, 30, 405-41 1. Brunelle. R. L.; Breedlove, C. H.; Midkiff, C. R. "Relative Aging of BallDOint lnks (A Preliminarv Studvl," .. a DaDer . . .Dresented at the 8th ~ n n i a l~eetingof the internat onal Cr m nal Police Organzation (IhTERPOL, in Paris. France. December. 1986.
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Journal of Chemical Education
examine inks scientifically? Suppose a bomb threat is received, or aransom note following a kidnapping. A suspect is arrested and a ball-point pen is found in his or her possession. Using thin-layer chromatography, described later in this paper, it is possible to compare the ink written on the threat note withasample of ink from the suspect's ball-point pen. If the inks match, this indicates that the inks are of the same chemical formulation, i.e., they are identical in composition. This is not to say that the suspect actually wrote the threat note, since many other pens will use the same formula of ink, hut i t adds to the circumstantial evidence that, combined with other evidence, could lead to a criminal's conviction by a jury. Analysis of ink written on a document is divided into two testing components: physical (nondestructive to the evidence) and chemical (semidestructive to the evidence). Physical examination of ink consists of 1. Visually noting the color of the ink, whichcan range form black to
white, with all spectral colors in between. 2. Observation of the way the ink sits on the document, using a variable-magnification, low-power (10-25X) binocular microscope. A trained observer can generally tell from this exam what type of writing instrument was used, e.g., fountain pen inks tend to "wick" out into the paper, while ball-point inks tend to sit up more on the surface of the paper.3 3. Examination under ultraviolet light (UV-360 nm) to see if the ink fluoresces, and, if so, with what intensity and color. Most inks do not fluoresce,hut some red inks will. One manufacturer purposely adds an opticalbrightener to his ink in order to distmguish it from that of other manufacturers. 4. Examination under infrared for transmittance, ahsorhance, or and exoensive luminescence. This reauires a biehlv - . soecialized . optical instrument, eqiipped with a variety of light sou&, filters, and T.V. camera. At this point, the physical examination of the ink has been completed, and i t is necessary to remove some of the ink from the document for chemicalexamination. If the ink is on a document such as paper, extremely small samples of ink are removed, using a hollow 20-gauge hypodermic needle that has had the bevelled tip removed from the end. Tiny dots or microplugs are bored out and removed from the paper, much as a miniature circular cookie cutter would be used. These microplugs, typically 8-10 per sample, are transferred one at a time to t a ~ e r e dsmall class or ~ l a s t i c vials for suhsequent extraction of the ink. ~ t - t h i spoint, it is required that a representative sample of the DaDer itself. free of ink, also be taken for a control.-~achmi&o&ug contains less than g of ink. One-half inch of writing contains, on the average, 1 pg of ink. Sampling by this hollow needle method described does minimal damage to the document and is scarcely noticeable on casual observation. If the dorument is held up to the light, the area where the ink samples were removed appear as tiny holes or perforations &the document. (It is a long established principle of law that evidence must be preserved as much as possible, not only for the trial, but also to allow the defense to do their own analysis if they wish.) ~ftersamplesofthequestionedentry ( Q )and ofthe paper control (C) have been placed in the vials. 5 to 10pLofsolvent
