706.5.6pp Glass & Soil F21.pdf

Glass & Soil Analyses n Forensic Glass & Soil Analysis n Grouped together → similar analytical techniques Both are common in burglaries. FOS 706 Professor Linda C. Rourke http://www.mobio.com/where_in_world/index.php http://www.chem.agilent.com/ca g/feature/0305/CA/Mar05_CA_forensics.htm 1 2...

Glass & Soil Analyses n Forensic Glass & Soil Analysis n Grouped together → similar analytical techniques Both are common in burglaries. FOS 706 Professor Linda C. Rourke http://www.mobio.com/where_in_world/index.php http://www.chem.agilent.com/ca g/feature/0305/CA/Mar05_CA_forensics.htm 1 2 Glass What is glass ? It is a non-crystalline super-cooled liquid. 3 http://www.jeetglassindia.com/bulletproofglass.html 4 Glass Crystals n atoms in a uniform array n crystal lattice http://www.indigo.com/models/molymodmolecular-model-kits.html http://foodchronicles.blogspot.com/2005_04_01_ foodchronicles_archive.html 5 http://www.yellow-springs.k12.oh.us/ysmls/microimage_12.htm 6 1 Glass n n Glass Glass - atoms irregularly spaced and randomly oriented Composed mainly of silicon dioxide (SiO2) Pure SiO2 is crystalline (quartz) Crystal Lattice of Quartz http://www.gc.maricopa.edu/earthsci/imagearchive/o,p,q.htm 7 8 Glass n n n Range of different compositions. Most are synthetic. Naturally occurring: volcanic n pumice (porous weak glass) n obsidian (dark glass) Glass Common sand: source material for manufacture of glass http://www.calstatela.edu/facult y/acolvil/igneous/pumice.jpg http://www.oregongeology.com /sub/learnmore/Obsidian.HTM http://en.wikipedia.org/wiki/Sand 9 10 Different Types Of Glass Different Types Of Glass Based On Varying Chemical Composition Some common examples: n n n n Soda lime glass Lead crystal Borosilicate glass Soda lime glass n 1st type of synthetic glass = silicon dioxide (quartz sand) + sodium carbonate (soda) + calcium oxide (lime) http://news.thomasnet.com/images/large/031/31117.jpg 11 12 2 Different Types Of Glass n Different Types Of Glass Lead crystal Contains lead oxide (PbO) n Sparkles due to high refractive index n http://www.georgian crystal.co.uk/crystalglassware/lead_cryst al_bowls.htm http://www.crystali magesinc.com/vases 1.htm 13 http://www.brainyclassrooms.com/i mages/products/16009-main.jpg 14 Different Types Of Glass Based On the Manufacturing Process Different Types Of Glass Based On the Manufacturing Process Sheet Glass n Plate Glass Tempered Glass 15 Sheet Glass n Glass blowing technique used to create cylinder shape n Cylinder is cut open, unrolled or flattened with gravity and cooled n Variation in thickness and defects in surface flatness. 16 Different Types Of Glass Based On the Manufacturing Process n Different Types Of Glass Based On the Manufacturing Process Plate Glass Molten glass is formed through rollers to desired thickness, cooled and then polished (expensive) n http://www.history.rochester.edu/ehpbook/shb/hb08.htm 17 Borosilicate glass - resistant to thermal shock = silicon dioxide with borax (sodium tetraborate); i.e. Pyrex Plate Glass Also prepared by the ‘float process’ (over a layer of molten tin metal producing very smooth surfaces) http://www.madehow.com/Volume-1/Automobile-Windshield.html 18 3 Different Types Of Glass Based On the Manufacturing Process n Different Types Of Glass Based On the Manufacturing Process Tempered Glass n n Heat treatment of formed item: Tempered Glass n heat until it begins to soften n then cool rapidly and uniformly with streams of compressed air n outside cools faster: stresses and surface tension n very strong and resistant to fracture n When it does break, fractures into many small cube like pieces; used as auto safety glass; only windshield is laminated glass http://www1.istockphoto.com/file_thumbview_approve/229 909/2/istockphoto_229909_auto_glass_shattered_2.jpg 19 20 Significance Of Glass As Evidence n n n n Significance Of Glass As Evidence Very frequently encountered due to its common usage Very brittle and easily broken Small glass particles are easily transferred since they can adhere to clothing Glass is very stable and not susceptible to environmental destruction 21 n n Glass is produced with a range of compositions and can therefore the forensic scientist can hope to approach an individualization Relevance as evidence: take into account inter- and intra-batch variation 22 Laboratory Examination of Glass Evidence Collection of Glass Evidence n n n n Most of the same precautions taken with other trace evidence during collection, need to be considered during the collection of glass evidence. Large pieces of glass should be packaged individually so as to maintain the integrity of the edges, which may be useful for reconstruction purposes. Details of the broken glass need to be fully documented before collection. Collect controls. n n Visually inspect; note gross characteristics: thickness, surface texture, color, curvature, frosted, wire reinforced, surface markings Determine if number and size of pieces are amenable to attempt a physical match http://www.plumpa rty.com/Merchant2/ graphics/products/l arge/17003.jpg 23 http://www.tritechre search.com/items/S MT1-FGP.JPG http://www.acidistri bution.com/images/ wireglass.gif http://www.lindabernard.com /imagesRS/NEWfruitSmall.jpg 24 4 Laboratory Examination of Glass Evidence n INDIVIDUALIZATION OF GLASS Aid in characterization of the glass samples, reconstruction, or individualization of the glass (compare questioned and known) in a jigsaw fit. n Physical Matches Random pattern of breakage - allows establishment of common origin – jigsaw fit n Examine 3-dimensional surfaces - rib and hackle marks n n Such marks will “match” along the mating fracture edges in a true jigsaw fit http://www.channel4.com/science/microsites/S/science/society/forensic_trace.html 25 26 Reconstruction from Glass Fracture Patterns Reconstruction from Glass Fracture Patterns Radial Fractures n n n n 27 Tangential (Concentric) Fractures n the third side of the triangle in which the other two sides are radial fractures n here the glass is under tension on the same side as the applied force, \ crack starts on same side as applied force Increasing force against a pane of glass, surface opposite point of contact will be under tension. When force is increased until tension exceeds tensile strength of glass, it will crack in two directions: propagate from side opposite the point of contact towards surface where force was applied At the same time it will radiate out from the center point. Result in several nearly triangular or pie-shaped sectors of glass. 28 https://w w w .sqaacadem y.org.uk/pluginfile.php/34022/m od_resource/content/2/G lass/fractures.htm l 29 30 5 De Forest, P.R., Gaensslen, R.E., & Lee, H.C. (1983). Forensic Science: An Introduction to Criminalistics, New York: MacGraw-Hill. Reconstruction from Glass Fracture Patterns Rib Marks n Curved lines on the fracture surface. n Starts perpendicular to glass surface where crack began and is nearly parallel to the surface where it terminates n Direction of propagation along the length of the crack is from the concave side of the rib pattern towards convex side. n Hackle marks are small marks perpendicular to the rib marks. n Radial fracture rib marks: http://www.channel4.com/science/microsites/ S/science/society/forensic_trace.html 31 32 Reconstruction from Glass Fracture Patterns n n Determining sequence of bullet holes through a glass pane Tempered glass will fracture to form small cube shaped pieces Determining sequence of bullet holes through a glass pane: http://www.pasarmored.com/Product_Sp ecifications.php http://www.americanphoto.co.jp/pages/onlinecat alog/Previews/glass-6.jpg 33 34 Reconstruction from Glass Fracture Patterns n Other Physical Features and Properties for Comparison n Differentiate mechanical fracture (radial/concentric) from thermal fracture (random pattern). Sheet glass: n ream marks = parallel striations visualized by optical methods De Forest, P.R., Gaensslen, R.E., & Lee, H.C. (1983). Forensic Science: An Introduction to Criminalistics, New York: De Forest, P.R., Gaensslen, R.E., & Lee, H.C. (1983). Forensic Science: An Introduction to Criminalistics, New York: MacGraw-Hill. MacGraw-Hill. 35 36 6 Other Physical Features and Properties for Comparison n Comparison of Known & Unknown Adhering materials n n n paint, putty, contaminants pattern of material or composition may be analyzed 37 n Comparisons based on differences in composition: difficult to do Measurement of physical properties may be more helpful than performing chemical analysis. 38 Nonoptical Physical Properties n Optical Physical Properties Density - mass/volume n Glass density is 2 or greater n Suspend glass in liquid of same density; compare to other sample n n Density gradient method n 39 Absorption (Transmittance) wavelength variation: can give it color n neutral absorption absorbs all wavelengths to the same extent and appear gray uncommon. n Fluorescence - float glass - side against tin will fluoresce. 40 Optical Physical Properties n Optical Physical Properties Refraction = Bending of light through the material n Refractive Index - is a term that compares the speed of light in vacuum to the speed of light in a particular medium (substance) speed of light in vacuum speed of light in medium n Refractive index = n RI cannot be less than 1 http://www.yourdictionary.com/images/ahd/jpg/A4refrac.jpg 41 42 7 Refractive Index Optical Physical Properties n https://micro.magnet.fsu.edu/primer/java/refr action/refractionangles/index.html Refractive Index Determination n n n n RI of sample depends on wavelength of light n n n n 43 Immerse glass chip in liquid of identical RI - it will appear to disappear. Determine RI of liquid using a refractometer Comparative RI determinations are more forensically important. this is dispersion RI inversely proportional to wavelength RI comparisons in white light are difficult →use monochromatic light 44 GRIM®3 GRIM®3 Glass Refractive Index Measurement n n n Uses the oil immersion/temperature variation method. The system operates through a standard laboratory microscope with phase contrast optics and a Mettler hotstage for temperature control. Using GRIM®3, repeat measurements produce results with a standard deviation of, typically, 0.00002RI. A laboratory instrument for high precision glass refractive index measurement. 45 46 Chemical Properties n 47 Soil Definition: n Any disintegrated surface material, both natural and artificial, that lies on or near the earth’s surface n Complex mixture of diverse particles. Instrumental methods of analysis can be used but physical methods have proven superior in sensitivity and reproducibility. 48 8 Soil Soil As Evidence Composition: n Organics Inorganics Artificial materials 49 n n Very commonly encountered type of transfer evidence Cannot be individualized Extremely large variation between different soil samples enhances the possibility of approaching an individualization 50 Collection of Soil Evidence n n Collection of Soil Evidence Visual inspection Control samples n n n extremely important the intrasample variation can be great n collect control samples at various intervals within a 100 yard radius of the scene n 1-2 tbsp/sampling n Alibi samples n n n 51 Specimens collected: Soil found on suspect n n n should be representative of soil found on suspect top surface layer is most likely to be relevant carefully preserve soil evidence wrap individual objects in paper, being careful that any loose particles will remain in the paper wrapping. Lumps of soil should be collected and preserved intact - layering effect provides greater evidential value. 52 Forensic Examination Of Soil Evidence n Analysis of natural & man-made particles n n n Forensic Examination Of Soil Evidence n rocks, minerals, vegetation, animal matter glass, paint chips, asphalt, brick fragments, and cinders The combination of materials listed above may impart to soil a composition unique to a certain area. n Soil and dried mud can be found adhering to suspect’s clothing or shoes, or to an automobile ==> can provide associative evidence linking a suspect or object to a crime scene. Requires careful comparative analysis with control samples taken from crime scene. http://www.mobio.com/where_i n_world/index.php 53 54 9 Forensic Examination Of Soil Evidence n Soil Analysis Geologists may be able to use soil evidence to determine the possible location of a crime if the crime scene is unknown. n n n n 55 Examine gross appearance side by side comparison: color & texture Estimated 1100 distinguishable soil colors \good starting point Soil color is darker when wet – compare dry samples Munsell color charts 56 Soil Analysis Soil Analysis Microscopic examination of soil n n n n Identify plant & animal materials, man-made debris. Forensic geologist can characterize minerals and rocks in the soil. 57 n Determination of mineral content provides significant points of comparison - adds to evidential value of a positive comparison Minerals naturally occurring crystals with unique physical properties: color, geometric shape, density, refractive index, birefringence n more than 2200 known minerals - most are rare; 40 or so are commonly encountered. n 58 Nonoptical Physical Properties n Soil Analysis Mohs Scale of Hardness: n 59 http://www.ascscientific.com/books.html Geological measurement scale n Scratching power n Suitable for mineral analysis n Can compare known and questioned sample hardness. n Most glass falls within a narrow range of hardness and therefore hardness is not often forensically useful n Rocks n n n composed of a combination of minerals. can exist in thousand of varieties on earth’s surface. identification made by characterizing the mineral content and grain size. http://www.ga.gov.au/education/minerals/i mages/moh.gif 60 10 Soil Analysis Soil Analysis Particle Size Distribution Density-Gradient Tube Technique http://www.tcreng.com/products/laboratorysoftware/microstructure-characterizer/particle-sizemeasurement.shtml 61 62 Evidential Value of Soil Evidential Value of Soil Number of comparison points and their frequency of occurrence are considered in judging commonality of origin. n n n 63 Forensic value of soil depends on it variation at a crime scene. If soil is indistinguishable for miles around it will have less evidential value. Best when some variation occurs every 10 - 100 yards. 64 11