Serial number restoration on polymer surfaces: A survey of recent literature

Modulating Reaction Kinetics Using an Electrolytic Method to Achieve Efficient Vehicle Identification Number Reappearance

Vehicle identification number (VIN) reappearance technology is an important means of vehicle traceability in various criminal cases. However, with the advancement of metallurgical techniques, the corrosion resistance of metal becomes stronger, and the traditional chemical etching reappearance method gradually fails. In order to break through the dilemma of traditional methods, this study establishes an electrochemical corrosion system by introducing the corrosion inhibitor hexamethylenetetramine (HMTA) to precisely regulate the electrochemical dissolution kinetics. Material characterization and electrochemical measurements demonstrated that the selective adsorption of HMTA significantly enhances the potential difference between plastically deformed regions and the normal metal substrate (ΔEmax = 6 mV). By effectively suppressing the corrosion rate in non-target areas, HMTA promotes selective anodic oxidation reactions in the vehicle identification number character regions due to their distinct microstructural characteristics, thereby substantially improving the contrast of the reappeared VIN markings. Density functional theory calculations and molecular dynamics simulations further reveal the formation of a dense adsorption layer, which is a key factor in improving the reproducibility of the results. The experimental results demonstrate that under conditions of 6 V applied voltage, with 0.5 M hydrochloric acid and 0.02-0.03 M HMTA in the electrolyte, efficient VIN reappearance could be achieved within 3-4 min on filed-down surfaces.

The effects of four different solvent vapours on the restoration of obliterated stamp markings from five different wooden surfaces

The stamp markings on wooden surfaces, which are placed on trees and products including antiques, indicate the status of trees and involve identifying data regarding the products. Such markings are obliterated either to facilitate illegal logging or to conceal product information. Despite the wide literature on the restoration of obliterated characters on metal and polymer surfaces, the recovery of defaced characters on wooden surfaces appears to be understudied. Several reference texts in the forensic marks' examination literature suggest that water, water vapor, and alkaline solutions are useful in restoring the abraded markings on the wood. Since there does not seem to be any experimental study proving such success, this study aimed to fill this gap. This study conducted experimental research by using water, ethanol, ammonia, and chloroform to recover the scraped characters on samples obtained from walnut, beech, spruce, oak, and cedar trees. The cold-stamped characters, which were defaced at varying depths, were restored using vapor and liquid phases of four solvents. While the vapor phases of water, ethanol, and ammonia yielded good outcomes on all types of wooden surfaces, the liquid phases did not seem to be useful in the revisualization process. The response of the vapors, which varied between 62 and 220 s, depended on the type of wood. The restoration technique developed in this research offers the possibility of on-site usage, easy application, utilization of low-cost solvents, rapid recovery, and effectiveness on various wooden surfaces. Overall, the restoration methodology used in this research appears to be fruitful in retrieving identifying information on wooden samples.

A spectroscopic approach for rapid and simple serial number restoration on polyamide 6 parts of firearms: The use of video spectral comparator 8000

Serial numbers have forensic value as they help to identify firearms. While the serial numbers are mostly stamped on the metal parts of firearms, the characters on polymer parts involve non-serial number information such as caliber, brand, model, or proof marks, which also serve for identification purposes. The forensic evidence indicates that the polymer frames of firearms bearing non-serial number information are obliterated through heating and scraping. Although the destructive restoration techniques for polymers are well-documented, there is little theoretical and practical knowledge regarding the non-destructive restoration techniques applied on polymers. In view of this gap, this study aims to devise a non-destructive spectral technique to recover the obliterated characters on Polyamide 6. Considering its wide use on polymers, the numbering is carried out by hot stamping and the numbers are defaced through heating, scraping, and hammering both superficially and deeply at varying depths. Herein, we focused on imitating the manual obliteration techniques used by criminals instead of the deepness-controlled techniques preferred by previous studies. The samples are then viewed under the UV and IR lights in the Video Spectral Comparator 8000 for the first time. The results suggest that spectral imaging provided restoration to a good extent after heating and scraping which made the characters invisible at a relatively low depth of deformation compared to hammering. The recovery of characters with this novel technique brings a new perspective forensic marks examination literature by producing quick, successful and reliable results and facilitating reexamination by not harming the sample.