Types of Glass and it's Forensic Analysis

Glass is an amorphous solid which is widely found as an evidence in the scene of crime. Glass holds significant forensic significance due to its prevalence at crime scenes and its ability to provide valuable evidence. Analysis of glass fragments, fracture patterns, and composition can help determine the sequence of events, source of impact, and even link suspects to a crime. This presentation consist of the types of glass encountered and it's forensic analysis.

1. GLASS and it’s Forensic Analysis. Shattering doubt, revealing certainty By- Adrita Dam.

2. INDEX SL. NO. TOPIC 01. What is Glass? 02. Manufacturing of Glass (Different Types of Glasses and their Compositions, Purpose and Application) 03. Forensic Significance of Glass 04. Collection and Preservation of Glass as Evidence

3. What is Glass? Introduction: It is a n amorphous solid structure. Typically transparent and brittle in nature. Also known as a Super-Cool Liquid as i t is immediately cooled of before it is turned into a crystalline-structured solid. The composition of Glass is mainly that of silica (silicon oxide)- additives like soda ash (sodium carbonate), lime (calcium oxide) are added to change the properties like brisance and tensile strength of the glass. Glass comes in various shapes and sizes and are used for various commercial production like cutlery set, bottle. Window pane etc.

4. Types of Glasses: Commercially used : Float Glass Glassware : Soda-Lime glass, Borosilicate Glass Safety Glasses : Polycarbonate, Trivex Prescription Eyeglasses : Plastic, Metal Alloys Sunglasses : Acrylic, Polarized Lenses Electronic Appliances : Tempered Glass Specialized Glasses : Optical Glasses, Solar Glasses, Display Glasses

5. COMPOSITION AND APPLICATION OF VARIOUS TYPES OF GLASSES.

6. Soda-Lime Glass It is composed of about 75% Silica (Silicon dioxide), 15% Soda (Sodium C arbonate), and 10% Lime (Calcium oxide). It is used in making of Glass-panes, Bottles, Containers, Tableware

7. Borosilicate Glass It is composed of about 80% silica and 13% boron trioxide. It has a higher melting point and lower coefficient of thermal expansion. Used in laboratory glassware, cookware, and high-quality glass lighting fixtures

8. It contains a significant amount of Lead O xide (PbO) along with Silica and other additives. The Lead content gives the glass brilliance and a higher refractive index. Its high refractive index makes it desirable for creating sparkling and intricate designs. Lead glass is renowned for its optical properties and is often used for making fine glassware, including luxury glassware, decorative items, and chandeliers.   Lead Azide Glass / Crystal

9. TEMPERED GLASS: Tempered glass is made from soda-lime glass but undergoes a thermal tempering process. It is heated to a high temperature and then rapidly cooled, creating internal stresses that strengthen the glass . Tempered glass is highly durable and resistant to mechanical stress, making it suitable for safety applications. It is used in automotive windows, shower doors, mobile phone screens, and architectural applications where safety and impact resistance are crucial

10. Laminated glass consists of multiple layers of glass with an interlayer of polyvinyl butyral (PVB) or ethylene-vinyl acetate (EVA) sandwiched between them. Laminated glass offers enhanced safety and security. When broken, the interlayer holds the shattered glass together, reducing the risk of injury. It is used in windshields, skylights, bullet-resistant glass, and soundproofing applications. LAMINATED GLASS:

11. Fibre Glasses: Fibre glass, or Glass Fibres , are composed of fine fibres of glass reinforced with a polymer resin. The glass fibres are typically made from silica, with additives to improve strength and flexibility. Fibre glass has excellent insulation and strength-to-weight ratio properties. It is widely used in insulation materials, composite materials, automobile parts, temporary roofs/shades, boats, and aerospace applications.

12. Specialized Glasses

13. Optical glass contains specific materials to achieve precise optical properties like great resolution, clarity, blue lens etc. These glasses are used for lenses, prisms, and optical instruments. OPTICAL GLASSES

14. SOLAR GLASSES: Solar glass is designed to maximize light transmission and minimize reflection in solar panels, allowing efficient conversion of sunlight into electricity.

15. DISPLAY GLASSES: Display glass, like Corning's Gorilla Glass, is chemically strengthened to resist scratches and damage, making it suitable for smartphones, tablets, and electronic displays

16. Forensic Significance of Glass

17. -The forensic significance of glass lies in its ability to provide crucial evidence in criminal investigations. -Glass fragments or residues can often be found at crime scenes, and analysing them can provide valuable information to help determine the sequence of events, identify sources, and link individuals to the crime. Here are some key aspects of the forensic significance of glass----

18. Trace Evidence: Glass fragments or residues can be left behind at crime scenes, on clothing, tools, or weapons used in the commission of a crime. These trace pieces can serve as crucial evidence linking suspects to the scene. Transfer of Glass : When objects come into contact with glass surfaces, glass particles can transfer between them. These transfers can occur during crimes such as burglaries, break-ins, or vehicle accidents . Glass Transfer and Trace Evidence:

19. Glass Fracture Patterns and Reconstruction: - Fracture Patterns : Glass fractures in distinct patterns depending on the type of force applied, such as impact, bending, or heat. Analysing fracture patterns can help determine the direction and sequence of events during a crime. - Reconstruction : By fitting glass fragments together, forensic experts can reconstruct the original object or determine the type of glassware involved. This reconstruction can aid in identifying the source of the glass and provide valuable information for investigations.

20. Refractive Index and Comparison: Immersion Method : Forensic scientists can use the immersion method to measure the refractive index of glass fragments. By matching refractive indices, they can determine if the fragments share a common origin. Refractive Index : Glass has a unique refractive index, which is the measure of how light bends as it passes through the material. Comparing the refractive index of glass fragments found at a crime scene to that of known samples can help establish if they originated from the same source.

21. Glass Composition and Source Determination: - Elemental Analysis : Analysing the elemental composition of glass fragments through techniques like scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) can provide insights into its chemical makeup. Different glass compositions can help identify the type and origin of the glass, such as window glass, automotive glass, or specialty glass. - Database Comparison : Comparing the elemental composition of glass fragments to a database of known glass samples can assist in narrowing down potential sources and identifying manufacturers or specific types of glass .

22. Glass as Forensic Toolmarks: Glass Toolmarks : Glass can retain impressions from tools used to break or manipulate it. These toolmarks can be analysed and compared to the tools recovered from a suspect or crime scene, potentially establishing a link between the tools and the crime. The forensic significance of glass lies in its ability to provide valuable evidence such as transfer patterns, fracture analysis, refractive index matching, composition analysis, and toolmark impressions. By analysing glass fragments and residues, forensic experts can contribute to crime scene reconstruction, source determination, and linking individuals to criminal activities.

23. Collection and Preservation of Glass: - Collection and preservation of glass as evidence is a crucial aspect of forensic investigations. Glass fragments, residues, or objects found at crime scenes can provide valuable information and link suspects to the scene. -Proper collection and preservation techniques are essential to maintain the integrity and evidentiary value of the glass evidence.

24. Safety Precautions: - Safety Gear : Investigators should wear appropriate personal protective equipment (PPE) such as gloves and safety goggles to avoid contamination and injury. - Avoid Cross-Contamination : To prevent cross-contamination, investigators should use clean tools and packaging materials for each separate glass item.

25. 2. Documenting the Scene : - Photography and Sketches : Before collecting any glass evidence, document the scene by taking overall and close-up photographs. Make sketches or diagrams to accurately depict the location and orientation of glass fragments or objects.

26.   3. Collection Techniques: - Tweezers or Forceps : Use clean, non-magnetic tweezers or forceps to carefully pick up glass fragments, taking care not to exert excessive pressure that could alter their shape or cause breakage. - Packaging : Place each glass fragment or object in a separate clean container or envelope. Clear plastic bags or small, sealable containers are commonly used for glass evidence. Ensure proper labelling with the case number, date, location, and a description of the item.

27. 4. Preventing Cross-Contamination: - Tools and Packaging : Use clean tools for each separate glass item to avoid cross-contamination. For packaging, ensure separate containers or envelopes are used for each distinct glass fragment or object. - Disposable Gloves : Change disposable gloves between handling different glass items to prevent contamination.

28. 5. Preservation and Transportation: - Fragile Glass Fragments : Fragile or small glass fragments should be packaged with care to prevent further damage. Place them in a padded container or envelope to minimize movement during transportation. - Larger Glass Objects : For larger glass objects, wrap them in protective material such as foam or bubble wrap to prevent scratching or breakage during transit. - Proper Labelling : Clearly label each package with the case number, exhibit number, description, and the name of the collector. Ensure the containers are sealed securely to prevent tampering or loss.

29. 6. Chain of Custody: - Documentation : Maintain detailed records of the collection, packaging, and transportation of the glass evidence. This includes documenting who collected the evidence, when and where it was collected, and who had custody of it at all times. - Secure Storage : Store glass evidence in a secure, controlled environment to prevent damage or loss. It should be kept away from extreme temperatures, humidity, and potential contaminants.

30. 7. Submitting to the Laboratory: - Contact the relevant forensic laboratory for specific instructions on submitting glass evidence. Follow their guidelines for packaging, labelling, and any additional documentation required. - Provide a detailed chain of custody record along with the glass evidence to ensure its integrity and admissibility in court.   Proper collection and preservation of glass evidence are essential to maintain its evidentiary value. Following these guidelines helps ensure the integrity of the evidence, facilitates accurate analysis, and enhances its reliability in the investigative process and potential legal proceedings.

31. REFERENCE Almirall , J. R., Trejos , T., & Lambert, K. (2020). Interpol review of glass and paint evidence 2016-2019. Forensic Science International: Synergy , 2 , 404–415. https://doi.org/10.1016/j.fsisyn.2020.01.010 Interpretation of Glass Evidence - Handbook of Trace Evidence Analysis - Wiley Online Library Forensic Examination of Glass and Paint | Analysis and Interpretation (taylorfrancis.com) Glass material and their advanced applications (researchgate.net)