Glass Examination - Essay Example

GLASS EXAMINATION Introduction Glass can be enormously helpful contact trace material in numerous types of offenses. A lot of offenses present the probability for glass particles to be transferred from something made of glass to the perpetrator. This is because, most often, robbers and criminals would penetrate their target victims by breaking glass windows or other structures of the vehicle or building. Based on studies, since glass evidence is most often encountered in offenses and crimes, the glass fragments recovered from the burglary tools, clothing(s) of the suspect, hair, shoes and others may be compared to known glass from the scene. Depending on the situations, the results can also disprove the accusation that an individual was implicated in an offense. The breakage characteristics of glass under impact crashes can create features which can be utilized as physical proof in several kinds of crimes. There are several glass examination techniques that can be used. Refractive Index is an efficient examination that can differentiate between various glasses. If the gathered glass particles varies in refractive index from a reference glass fragment, then, these glass particles could not have came from the same piece of glass. Chemical examination gives detailed information regarding the chemical compositions of the glass. The chemical analysis can be utilized in order to differentiate between glass samples which possess the same refractive index, however with different chemical composition. Current advances in forensic science reveal that the use of analytical techniques in forensic laboratories continues to add to the discerning supremacy of this approach. In addition, the surfaces of glass fragments can be microscopically examined for evidence of the method of manufacture and the type of object from which they came. Flat glass and patterned glass are from window panes. Curved glass is for drinking glass or bottle. Further tests may be performed to see if the source was of toughened glass. This is a glass forming small cubes when broken and usually found in some car windows and in door and window glazing. Types of glass are flat glass, tableware glass, container glass, optical glass, specialty glass and decorative glass. Variation in manufacture of glass allows considerable discrimination even with tiny fragments. Data and Results: Table 1. Data Gathered on Clothing Observer Color Type Composition / Base Material Presence of Glass 1st student - Taryn Grey stripped vest top 54% cotton 40% polyester 3% polyamide fiber NO GLASS Grey wooly polo neck top 38% polyester 3% Alsatian TWO PIECES OF GLASSES Green long sleeve top 100% cotton NO GLASS 2nd student - Heather Purple cardie pockets 75% polyester 25% cotton NO GLASS Purple jumper 100% cotton NO GLASS Black vest top 95% cotton 5% elastane NO GLASS jersey T-shirt 100% nylon 3 PIECES OF GLASSES 3rd student - Scott Adidas T-shirt 100% polyester ONE PIECE OF GLASS Underarmor 63% nylon 23% polyester 14% elastine ONE PIECE OF GLASS 4rth student-Me Yellow T-shirt 100% cotton NO GLASS blue T-shirt 100% cotton NO GLASS Yellow T-shirt 100% cotton NO GLASS In this study four students observed tops. The above table reflects their observations. Glass examination like this is done by forensics. Forensic glass examinations involve a comparison of samples from known and questioned sources. Importance of Glass Examination to Forensic Scientists Glass examination is important to forensic scientists since the glass recovered from the clothing, for example of a hit and run victim. may be compared to the known glass from the suspect’s vehicle. During glass examination, the glass type is determined. Glasses are classified as tempered glass, container glass, and others. The forensic scientist can also determine the direction of force used to break the glass or the order and direction of projectiles fired through the glass. Another good determination is the similarity between evidence glass and standards. The fracture physical match of the glass samples can also be a good determination. Analysis When a glass is wrecked, small particles of that glass can be projected towards the perpetrator’s body, specifically footwear, clothing, hair and even on pockets. Other people in close proximity can also gathered glass fragments. The distance of the projection, according to studies is at least one and a half meter up to three meters away. The quantity of glass fragments that can accumulate on people reduces quickly with distance from the breaking glass. Also, backwards projection of fragments towards the perpetrator can also be acquired by climbing through a wrecked window or through walking on pieces of broken pane. If the gathered glass particles match the reference sample during forensic examination using the Refractive Index and through analysis of the chemical composition, it will be essential, therefore, to find out how uncommon / unique or not the pane might be. In order to conduct this, the forensic examiner may refer to a computer database showing the joint results of both the Refractive Index measurements and the chemical analysts’ for every reference glass sample examined under his laboratory. This will demonstrate how frequent a particular kind of glass has been came across. It should be noted, however, that this is not automatically a trustworthy suggestion of how frequent it might be. The rationale of this is that the majority of glass samples forwarded to forensic laboratories came from wrecked windows. Some studies revealed that pane fragments recovered from clothing materials by chance is more probably came from a glass bottle or container. Also, there be inclined to be local pockets of particular kinds of panes. A good example of this is that glass which came from buildings all built at the same time. It should be noted that the information and data that can be found on the database might be out of true, hence, they should be handled with enough prudence. The examiner will also required to consider the number and distribution of the glass fragments that the investigator recovered as well as whether this fits in with the alleged circumstances. These are done aside from looking at the data and information from the database. When the evidences were gathered like the plenty of glass particles found from the perpetrator detained within a few hours of the occurrence of the offense or crime, then the evidence will be very strong. A good example of this is if the glass is unusual and or there is more than one type of matching glass. Hence, in instances when the evidences were gathered several days after the commission of the offense or the crime, less weight is given to these To further explain, experts often suggest that glass particles might be conveyed between persons who come into contact to each other after the offense or crime has occurred. For instance, when these two persons journeyed alongside in an automobile bring them to the police station. However, only a few glass particles are most probable to be relocated via close contact. Likewise, only a few glass fragments may linger on the chair or place occupied by the contaminated suspect. Previous studies reveal that the percentage of retained glass depends on the size of the fragments. Particles between 1 and 0.5 millimeter in size are retained for the longest time. why this information is important to forensic scientists.1 Fragments smaller than 0.5 millimeter are not retained longer. This is because there could be a critical size for the retention of fragments or that very small fragments are difficult to see under a microscope. Glass is not transfer by breaking a window. It is necessary to study the transfer and persistence of glass fragments on garments under more realistic breaking conditions. As discussed above, when a perpetrator breaks a pane or has contact with wrecked glass particles, these fragments can be transferred to suspect’s garments. Hence, during these cases, it is imperative for the investigators to search for the glass fragments. Searched materials can be hair, clothing, instruments / tools. The investigator can then analyze the glass fragments recovered in order to establish the link of the glass particles found on the suspect with that glass fragments gathered from the crime scene. A good example of which is that in instance of a house burglary, the wrecked glass fragments gathered from the perpetrators’ garment would be compared with the glass from the pane at the place where the offense or burglary happened. This is referred to by the forensic examiner as the control sample. The glass can be examined in a number of different ways, such as physical matching, refractive index and through the use of the scanning electron microscope (SEM). Physical Matching To date, physical matching still stands as the best ultimate ways of setting up a common source amid or among some samples. When the examiner can match the two samples of glass together to form one item, therefore, the examiner can determine that “the samples have only originated from that one item and nowhere else“.2 Aside from this type of physical matching, the examiner also look at the physical characteristics of the gathered particles of glass. These physical properties include thickness as well as color. Refractive Index The degree to which light is refracted as well as how light bends as it enters the glass can be utilize as a means of examination. Theoretically, “each kind of glass will refract the light differently and will have its own refractive index“. This refractive index of glass is determined via the use of an instrument. This instrument is called the GRIM or the Glass Refractive Index Measurement.3 Studies revealed that if two pieces of glass posses the same refractive index, then the examiner can deduce that the fragment of glass came from the same source. Scanning Electron Microscope The Scanning Electron Microscope4 is usually utilized in forensic examination. This is preferred when analyzing the elemental contents of the glass. This microscope is a good tool since it provide quick analysis of the elements that compose very small glass fragments. It also provides beyond question examination of the source of the pane materials that are critical to the sequence of substantiation. It also gives three-dimensional (3-D) images of extremely small glass structures or fragments.5 Further Evidence The glass fragments examiner can likewise establish from which side of the glass a pane was wrecked. This is done by closely examining physically the crack marks on the conked out edges. These wrecked glass particles can also present other important forms of proof for the forensic examiner. Such other forms of evidences can be other marks, blood, hair strands or clothing fibers that have been trapped on the jagged edging of the pane. Using their specialist skills the forensic scientist can analyze this evidence and help to uncover vital clues to solve the crime. Conclusion Glass examination is done in order to determine if the glasses originated from different sources. The matching of glass fragments engages the acknowledgment as well as examination of class properties that link materials to a batch. The establishment of the link is by no means to only one source. Likewise, individual distinctiveness of glass examined permit the connection between or among two or several objects with each other or among each other to the ruling out of all other objects. For the one examining the glass, this instance can only happen at a time when there is a match between or among pieces of glass. Since there is intrinsic heterogeneity of physical and chemical properties contained by one source of pane, therefore, it is important to put emphasis to the importance of gathering as well as analyzing a sample / samples of the known source. This is done in order to compare to whichever gathered glass particles. It can be observed from the data gathered the clothing with high polyester or nylon has the presence of glass. Studies shows that wooly material has the tendency to retain glass as compared with cottony materials. Bibliography American Academy of Forensic Sciences, Welcome to the Fascinating World of Forensic Science, Forensic Sciences Foundation, Inc., Colorado, 1996. Caddy, Brian, Forensic Examination of Glass and Paint: Analysis and Interpretation, CRC Press, London, 2001. Curran, James Michael, Champod, Tacha Natalie Hicks and Bucleton, John S., Forensic Interpretation of Glass Evidence, CRC, 2000. Nokes, L.D., Green, M. et al., The Use of Scanning Electron Microscopy in the Dating of Human Skeletal Remains, J. Forensic Science Soc., vol. 27, issue 6, pp. 413-416. Robertson, Bernard and Vignaux, G.A., Interpreting Evidence, John Wiley and Sons, 1995. Read More