The Effect of Ultraviolet Radiation on the Microspectrophotometry (MSP) of Dyed Fibers
Microspectrophotometry
A common microanalytical technique for forensic fiber characterization and comparison is color analysis through microspectrophotometry (MSP). A microspectrophotometer allows the analyst to non-destructively acquire color information and spectra of small areas of single fibers.
Figure 1. Sample board with dyed Testfabrics swatches, samples A1-A10 at Time = 0.
The MSP spectrum, resulting from colored dyes and mixtures of colored dyes, can be compared with spectra from the same or other fibers. However, little is known about changes in dyed man-made fibers that result as an effect of environmental conditions, especially exposure to ultraviolet (UV) radiation over long periods of time.
This research uses a microspectrophotometer to study the effect of ultraviolet radiation on a variety of dyes commonly used to color fibers. Fibers were monitored and sampled every eight weeks for MSP analysis over an 18-month period of exposure to artificial UV radiation in the laboratory (following ASTM G154-12a guidelines) and real sunlight outdoors (following ASTM G7 guidelines). Changes in visual color and spectral changes detected and plotted by the microspectrophotometer were statistically and visually evaluated for differences attributed to the photodegradation of the dyes.
Figure 2. Ten sample boards with Testfabrics swatches in position at Q-Lab Test Services in Arizona, October 2017.
Approximately 60 known, dyed, textile fabrics were exposed to UV radiation for the duration of the study. The chosen fabrics represented the most commonly used dyes on man-made synthetic fibers. Fabrics were selected from a reputable and traceable fiber reference collection. Additional fabric swatches were custom dyed to specifications by a textile test materials company. MSP spectra of UV-exposed fibers include the visible and ultraviolet regions for analysis. Spectra were collected at regular eight-week intervals and compared to unexposed (control) spectra. SWGMAT guidelines were followed, when applicable. This study provides an applied practical understanding of how ultraviolet radiation can affect the dyes and color of fiber evidence and improve the discrimination, identification, and individualization of man-made polymer fiber products for the forensic scientist.
This project was supported by Award No. 2016-DN-BX-0145, awarded by the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice. The opinions, findings, and conclusions or recommendations expressed are those of McCrone Research Institute and do not necessarily reflect those of the Department of Justice.