Methods of Forensic Materials Analysis

The methods of Forensic materials analysis range from microscopic examination to X-ray diffraction. The methods are described in articles such as Macroscopic examination of samples from fires, Detection of added ignitable liquid residues in fire samples, and X-ray diffraction.

X-ray diffraction

X-ray diffraction is a nondestructive technique that can identify the composition and purity of a compound. The technique is especially sensitive to polymorphs, or materials that are chemically similar to one another, and it can be used to analyze small samples or large amounts of material. A typical microdiffractometer system includes two or more devices that allow a sample to be fixed, scanned, or rotated.

ESEM

ESEM is a useful tool for Forensic materials analysis. Its unique characteristics make it suitable for the analysis of non-metallic, biological, and uncoated samples. Compared to conventional SEM, which operates under a vacuum of 10-3 to 10-4 Pa, ESEM works at a gas pressure of up to 500 Pa. This low-pressure environment allows it to work with samples without charging them or destroying them.

Macroscopic examination

Macroscopic examination is a procedure that uses various types of microscopes to identify forensic materials. For example, a contact shot will leave a characteristic tear called a "cruciform tear." Microscopy can determine gunpowder residue and other materials that have been used in the crime. Chemical tests can identify substances such as copper, lead, or nitrites.

Detection of added ignitable liquid residues in samples from fires

Detection of added ignitble liquid residues (ILRs) in samples from fires is an important analytical technique that can provide valuable information for fire investigation. This technique can help confirm the field investigator's conclusion on the origin of a fire by identifying the ignitable liquid residues present in the fire debris. Additionally, detection of ILRs can help in assessing the fuel load of the fire.

Gunshot residue analysis

Gunshot residue is the material that remains on the body after a firearm has been discharged. It includes particles of the primer, gunpowder, projectile, and cartridge case. Of these, primer particles are the most forensically significant. Unlike primer residue particles, gunshot residue can't be linked to a specific firearm or ammunition because they are all made from the same basic materials.

Footwear impressions

Footwear impressions are used to help identify a specific piece of footwear, including its size, make, and manufacturer. This information can help to narrow down a list of suspects and potentially link several crime scenes. For instance, the examiner can determine whether the shoe has the same outsole design as another known shoe.

Discrimination between striations and impressions

In forensic science, discrimination between striations and impressions is the process of comparing and evaluating the similarities and differences of two marks. The two types of marks are formed by varying processes such as compression and impact. The method relies on a population database with representative marks to ensure reliability and consistency. However, different laboratories may use different databases and thus produce different statistical results. To overcome this problem, NIST, in collaboration with FBI and NFI, developed a software package known as Scratch, which can compare and contrast striations with impression marks.

Using fractography

Fractography is an analytical technique used to examine fractures in materials. Its resolution is much higher than an optical microscope, which makes it useful for examining small areas in a single scan. This technique is used for materials with high sensitivity, including biological and biomedical specimens. Using fractography is an important part of forensic materials analysis because it can help determine the point of failure and clues about why a part failed. It is also non-destructive and affordable.