Identification of Dyes and Pigments Found in Inks Used to Label Iron Pipes: Implications in the Analysis of Pipe Bombs

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ABSTRACT

When a pipe bomb has been detonated, a variety of evidence can be collected including burned and unburned powder, trigger mechanism(s), and parts of the actual pipe body and end caps. Iron pipe, commonly used in the construction of pipe bombs, has information printed on it in a variety of ink colors. The dyes used in the inks can be characterized, providing additional information that may link a type/size of pipe with a local hardware store where pipe imprinted using a particular dye is sold. The present article discusses approaches for removing ink from an iron pipe, and generating chemical information such as a UV-Visible spectrum, thin layer chromatographic data, and mass spectral data. In some cases, spectra of unknown inks can be matched with those from locally-obtained samples. In other cases, the actual dyes used can be identified and matched with those used by manufacturers to print on pipe. Dyes used in ink printing on pipes provide an additional tool for gathering information on the possible manufacturer of a pipe bomb.

Approximately 75% of all bombs used in the United States are home-made pipe bombs, accounting for several hundred bombings a year (Committee on Smokeless and Black Powder, National Research Council, 1998). This is not surprising in light of the many web sites available describing both their construction and the ease with which components can be secured. In the extensively-covered incident at Columbine High School, the arsenal of weapons accumulated by the students included 27 pipe bombs. Because of their simplicity and potential for damage (Gibbons, Farrier, & Keys, 2003, Oxley, Smith, Resende, Rogers, Strobel, & Bender, 2001), the National Research Council (NRC) issued a request for additional research that could lead to both the detection of pipe bombs and the arrest of pipe bomb makers (National Academy of Sciences, 1998).

The scene of a pipe bomb explosion provides a potential plethora of evidence--unburned powder, products of the combustion reaction, the fuse/trigger mechanism and tape, as well as pipe and end cap fragments. Recently, it was shown that sufficient DNA is transferred to a pipe bomb during handling and construction, and that the DNA present can be analyzed post-blast (Esslinger, Siegel, Spillane, & Stallworth, 2004). Sophisticated instrumental methods such as micellar electrokinetic capillary electrophoresis have been evaluated for matching postblast residue to specific powders used as the explosive charge in pipe bombs (Smith, McCord, MacCrehan, Mount & Rowe, 1999). It is an unfortunate fact, however, that the uses of pipe bombs continue to be redefined. For example, a report has appeared in the National Association of Medical Examiners Journal of a suicide by pipe bomb (Davis, Rollins, Reiber, & Anthony, 1999).

Thick-walled iron pipe, ideal for bomb construction, is readily available at local hardware stores. Wrought iron pipe, used for water supply in older houses, can be used, although cast iron pipe, used for sewer lines and municipal water conduits, is more commonly employed. Fixed lengths of pre-threaded cast iron pipe are readily available, and many stores can cut and thread pipe on request. Caps built to fit common iron pipe sizes are readily available as well.

American Society for Testing and Materials (1998) standards require that every length of pipe carry information on the manufacturer, country of origin, dimensions, and intended usage. For iron pipe, the information can be cast, engraved or printed. Printing is now a common method for labeling, with a variety of methods such as inkjet printing now available to pipe manufacturers. Iron pipe is largely manufactured in China, Mexico, the United States and Canada.

The ink used to print on iron pipe represents additional evidence and information. A number of ink colors can be seen on iron pipe at hardware stores. If the ink can be identified and related to a manufacturer, and pipe from that manufacturer is sold local to the crime scene, one may be able to search records at nearby stores to determine if such pipe was recently sold. …