•Novel method for determining the detection limit of the luminol for bloodstains.•Bloodstain samples were prepared reproducibly using a novel technique.•Blood-luminol chemiluminesence was captured by a CCD camera and quantified.•Detection limits are reported in unit of dilution factor and weight % blood solid.•Even low response from a blood reagent test is worthy of further investigation.The luminol test has been used for over 60 years by forensic investigators for presumptive identification of blood and visualization of blood splatter patterns. Multiple studies have estimated the limit of detection (LD) for bloodstains when luminol is employed, with results ranging from 100× to 5,000,000× dilute. However, these studies typically have not identified and controlled important experimental variables which may affect the luminol LD for bloodstains. Without control of experimental parameters in the laboratory, variables which affect the potential of presumptive bloodstain test methods remain largely unknown, and comparisons required to establish new, more powerful detection methods are simply impossible. We have developed a quantitative method to determine the relationship between the amount of blood present and its reaction with luminol by measuring, under controlled conditions, the resulting chemiluminescent intensity with a video camera, combined with processing of the digital intensity data. The method resulted in an estimated LD for bloodstains on cotton fabric at ∼200,000× diluted blood with a specific luminol formulation. Although luminol is the focus of this study, the experimental protocol used could be modified to study effects of variables using other blood detection reagents.Download high-res image (79KB)Download full-size image

Audio recordings are a significant component of the world’s modern cultural history and are retained for future generations in libraries, archives, and museums. The vast majority of tapes contain polyester-urethane as the magnetic particle binder, the degradation of which threatens the playability and integrity of these often unique recordings. Magnetic tapes with stored historical data are degrading and need to be identified prior to digitization and/or preservation. We demonstrate the successful differentiation of playable and nonplayable quarter-inch audio tapes, allowing the minimally invasive triage of tape collections. Without such a method, recordings are put at risk during playback, which is the current method for identifying degraded tapes. A total of 133 quarter-inch audio tapes were analyzed by attenuated total reflectance Fourier transform-infrared spectroscopy (ATR FT-IR). Classification of IR spectra in regards to tape playability was accomplished using principal component analysis (PCA) followed by quadratic discriminant analysis (QDA) and K-means cluster analysis. The first principal component suggests intensities at the following wavenumbers to be representative of nonplayable tapes: 1730 cm–1, 1700 cm–1, 1255 cm–1, and 1140 cm–1. QDA and cluster analysis both successfully identified 93.78% of nonplayable tapes in the calibration set and 92.31% of nonplayable tapes in the test set. This application of IR spectra assessed with multivariate statistical analysis offers a path to greatly improve efficiency of audio tape preservation. This rapid, minimally invasive technique shows potential to replace the manual playback test, a potentially destructive technique, ultimately allowing the safe preservation of culturally valuable content.

Thermal imaging is not ordinarily a good way to visualize chemical contrast. In recent work, however, we observed strong and reproducible images with chemical contrasts on blood-stained fabrics, especially on more hydrophobic fabrics like acrylic and polyester.

•It is possible to differentiate spectra obtained from a microspectrophotometer for fibers with different concentrations of the same dye.•Classification using chemometric methods was the most accurate by defining three classes of fibers having low, medium, and high dye loadings.•It was possible to discriminate pairs of exemplars as questioned (Q) versus known (K) comparisons.Microspectrophotometry is a quick, accurate, and reproducible method to compare colored fibers for forensic purposes. Applying chemometric techniques to spectroscopic data can provide valuable information, especially when looking at a complex dataset. In this study, background subtracted and normalized visible spectra from ten yellow polyester exemplars dyed with different concentrations of the same dye ranging from 0.1% to 3.5% (w/w), were analyzed by agglomerative hierarchical clustering (AHC), principal component analysis (PCA), and discriminant analysis (DA). Systematic changes in the wavelength of maximum absorption, peak shape and signal-to-background ratio were noted as dye loading increased. In general, classifying the samples into ten groups (one for each exemplar) had poor accuracy (i.e., 51%). However, classification was much more accurate (i.e., 96%) using three classes of fibers that were identified by AHC as having low (0.10–0.20 wt%), medium (0.40–0.75 wt%), and high (1.5–3.5 wt%) dye loadings. An external validation with additional fibers and data generated by independent analysts confirmed these findings. Lastly, it was also possible to discriminating pairs of exemplars with small differences in dye loadings as a simulation of questioned (Q) versus known (K) comparisons.Download high-res image (143KB)Download full-size image

•Artificial fingerprints are imaged via steam thermography.•Microscale steam thermography images individual print ridges.•Cotton, a difficult subject fabric for steam thermography, is analyzed.Steam thermography is used to image ridge patterns of blood-transferred artificial fingerprints on acrylic, polyester and cotton fabrics. Microscale thermal imaging confirms that the ridge patter transfer occurs on the tops of the most prominent threads in weave. Prints are readily imaged on the more hydrophobic fabrics in both heat-up and cool-down phases of vapor exposure. On the more hydrophilic cotton fabric, ridge detail is obscured by the strong background response of the fabric to moisture. Microscale thermography reveals that loose cotton strands with transferred blood may respond differentially to moisture relative to uncoated strands.Download high-res image (215KB)Download full-size image