Module 3_Forensic Examinations

7/27/2019 Module 3_Forensic Examinations

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Introduction to Glass Examinations

Fracture Match, Isotropy, Sn, Curvature, Bugs

Fluorescence, Density, Refractive Index

Calibration of the GRIM2/GRIM3 System

Module # 3


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Problem

A. The accurate association of a questioned

glass fragment(s) to a source of glass.The questioned glass is analytically indistinguishablefrom the glass source that was submitted as a standard

B. The assignment of a value of strength forthat association.

The frequency of occurrence for the RI is 4 % and

the frequency of occurrence for the [Zr] is 8 % ...or

The glass evidence (strongly) supports the hypothesis of

contact with the source of the broken glass rather than not


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Glass Analysis

Visual Inspection of Known/ Questioned forFracture Matches

Comparison of Glass:

Physical Properties

Optical Properties

Chemical Properties

Classification of Glass into End Use Category

Discrimination between glass samples

Interpretation and Value of Results


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Glass Fracture Characteristics

(Terminology, Significance, Limitations)

Crime Scene Reconstruction(Direction of Force, Sequence of Shots,

Laminated Glass Considerations)


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Radial and Concentric cracks

Elasticity permits bending until radialcracks form on the opposite side of theforce

Continued force places tension on thefront surface (force side), forming theconcentric cracks


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Conchoidal Striations (fractures)

Source: Forensic Examination of Glass and Paint. Caddy, B. Ed.;

Taylor & Francis: London, 1999.


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Direction of force determination

The perpendicular edge always facesthe surface on which the crackoriginated




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Direction of force determination

The perpendicular edge always facesthe surface on which the crackoriginated




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The 3R Rule

Radial cracks form a Right angle on theReverse side of the force

Need to know: 1) Which side of the window is examinedNeed to know: 1) Which side of the window is examined

2) Whether a radial or a concentric edge is examined2) Whether a radial or a concentric edge is examined

Source: Forensic Examination of Glass and Paint. Caddy, B. Ed.;Taylor & Francis: London, 1999.


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Conchoidal Striations



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Exceptions to this rule

Tempered glass because it dicesand a

frostin the middle prevents theobservation



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Other exceptions

Very small windows held in a tightly heldframe

windows broken by heat or explosion

Laminated glass is a special case:

There are two glass sheets sandwiching a

vinyl film. The sheet opposite the forceexhibits the fracture marks.


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Plastic Identification and Sn surface

Plastic can be eliminated by testing forindentation by a needle point

Fluorescence upon short wave (254nm)illumination of an original surface can

detect the Sn contamination on one sideof float glass.


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Interference Objective

An Interferometer can be used to detectthe most minimal curvature on the glasssurface

Curvature indicates possible sources:windshield

containersother non-flat glass source


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Thickness Considerations

Tempered glass is greater than 3.0 mmthick

Vehicle side windows are typically 3.3-

3.6 mm thick

Tolerances: 3.0 mm (2.92 - 3.41mm)

4.1 mm (3.96 - 4.17 mm)Typical auto standard is +/- 0.003 inches.


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Bugs- Manufacturer Identification


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Bugs-DOT numbers on vehicle glass


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Density Measurements

High correlation between D and RIobserved

Literature review

Slater and Fong (1982)

Stoney and Thorton (1985)

Koons and Buscaglia (2001)


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RI (nD) and Density correlationRI (Nd) v Density (USA casework)

2.4

2.45

2.5

2.55

2.6

2.65

1.505 1.51 1.515 1.52 1.525 1.53 1.535

RI (Nd)

Density


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Density Method

Sink/Float

Vary the mix of two liquids having differentdensities until the K fragment floatsin themixture

Place Q in same solution and determine if itfloats

At that point, the density of the liquid andglass (K and Q) are equal


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Density Determination

Once fragments match, their densities are

equal and the density of the liquid can bedeterminedPlummet and balance method

Digital densitometer method

Do we really need to know the density?Is it better as a comparative exam?What is the variability of a source?

How reliable are results for small fragments?


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Density Liquids

Methylene Iodide d ~ 3.32 g/cm3

Bromoform d ~ 2.85 g/cm3

Acetylene Tetrabromide d ~ 2.96 g/cm3

Sodium Polytungstate d ~ 2.89 g/cm3

Na6H2W12O40x H2O (water soluble)


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Non-Toxic Float liquid

Poly Gee Brand; Sodium Polytungstate

density = 2.89 g/ml

non-toxic

adjustable density (with addition of water)reusable (evaporate water)

~ $ 100.00 / lb sold as solid or liquid from:

Geoliquids Inc., 1618 Barclay Blvd.

Buffalo Grove, Illinois 60089 - (708) 215-0938


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Density Discrimination of

Samples with Similar RIs

SAMPLE SOURCE TEMPER FLOAT nD nC nF DENSITY

W-8 RESIDENCE N N 1.51666 1.5140 1.5228 2.4844

W-38 RESIDENCE N N 1.51665 1.5140 1.5229 2.4881

Data from S. Ryland, FDLE


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Characterization of Glass Fragments

Refractive Index Determination(GRIM and GRIM2, Foster and Freeman)

Elemental Composition by sensitive method

(XRF, ICP-AES, ICP-MS)

Application of Statistical Techniques

(Classification Schemes, Descriptive

Statistics (Graphical), Match Testing,

Informing Power Statements)


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Beck Line Method (1892)

When the objective of the microscope israised (focus up), a bright line movesinto the direction of the material of higher

R.I.Once the line disappears or doesnt move,the R.I. of the oil can be measured by a

refractometer.The Beck line is best observed with

contrast microscopy.


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Emmons Temperature VariationMethod (1930)

Emmons observed the variation of R.Iwith temperature ( temp, R.I.) for oilsbut not (much) for glass.

He used a circulating water bath to heatthe oil with an immersed glass in it andwatched for the Beck line to disappear.(He then measured the oil R.I. with arefractometer at that temperature)


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Emmons Double Variation Method

Used with a Mettler Hot-Stage for bettertemperature control and involved thevariation of both the wavelength of the

light coming through the sample and thetemperature.

(Description of method in handout, Theory description in

Safersteins Handbook)


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Refractive Index

RI of glass is known to be affected byboth wavelength and temperature

nmatch temperature

n25

wavelength

D


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Dispersion (V)

The relationship of the indices at differentwavelengths.

(nD - 1)

(nF - nC)where: nD is measured at 589 nm (SodiumD line)

nF is measured at 486 nm (blue)and nC is measured at 656 nm (red)

V =V =


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Value of Dispersion

dispersion data does not provideadded discrimination... large error

inherent in dispersion data

dominates the error associated withthe k value

Cassista et al, Canadian Society of ForensicScience J ournal, Vol. 27, No. 3, 1994


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Refractive index oil immersion method

Immerse the selected fragment in a previouslycalibrated silicon oil and mount on a slide for viewingunder phase contrast microscopy.

Change the temperature of the oil in a controlled

fashion to reach the endpointwhere the RI of the oil isequal to the RI of the glass (viewed as maximum

contrast).

Use the calibration curve for the oil to interpolate the RIof the glass.


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Phase Contrast Microscopy


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Calculating the Mean Match

Temperature

Temperature

Mean Match

Temperature

ImageContrast

Cooling CycleHeating Cycle


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Oil Immersion at the Match

Temperature


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Calculating the Mean Match

Temperature

Temperature

Mean Match

Temperature

ImageContrast

Cooling CycleHeating Cycle


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Oil Calibration

Temperature

RI

Glass

Oil

Match Temp


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Oil Calibration

Temperature

RI

Glass

B Oil Match Temp

1.52

1.49

1.54

C Oil

A Oil

25 60 110


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Locke Silicone Immersion Oils

Oil A nD

25=1.540

nD range 1.53990 - 1.55663

Oil B nD25=1.520

nD range 1.50187 - 1.52903

Oil C nD25=1.481

nD range 1.46409- 1.48652(Locke Scientific or Foster and Freeman)


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Oil Operating Temperatures

A Oil RI - 1.552 360

C1.534 800C

B Oil RI - 1.529 390C

1.502 1120C

C Oil RI - 1.486 460C

1.464 1070C


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RI determination by GRIM2 Good Precision: SDs of 0.00002 over 5 hr.

period (using optical reference glass) and0.00003 over 5 days.

Fast analysis routine (~ 5-10 min. / reading)

Semi-automated, reduced operator bias Improved data handling, reduces transcription

errors, facilitates data manipulation

Published by ASTM E-30 as a standardmethod of analysis.


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Proficiency Test Results (R.I.)

1993 (23 of 71 labs used GRIM or GRIM2) 1994 (31 of 88 labs used GRIM or GRIM2)

1995 (39 of 95 labs used GRIM or GRIM2)

(7 labs reported elemental analysis)

(7 labs reported use of statistical analysis)

1996 (46 of 106 labs used GRIM or GRIM2)(40 labs reported elemental analysis)


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Analytical Requirements for Classification

Classification requires good accuracy, but not

necessarily good precision. The best elementsfor classification are those added by themanufacturer to effect a desired end-useproperty, ex. B in headlamps, Ba in TVscreens or Ce in decolorized glass.

Interpretation of results requires access to ahigh-quality database.


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Analytical Requirements for Discrimination

Discrimination requires excellent precision, but

does not generally require good accuracy. Thebest variables for discrimination are those nottightly controlled by the manufacturer, but foroptimum discrimination, the maximum number

of variables should be determined. Allmeasured variables must be indistinguishablefor a common source to be indicated.

Factors Affecting Classification


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Factors Affecting Classification

Capability Analytical accuracy over long time period

Consistency of analytical method over time Within-class heterogeneity (not within-sample)

Distinctiveness of variables (not number)

Completeness and accuracy of database Contamination control

Factors Affecting Discrimination


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Factors Affecting Discrimination

Capability

Shortterm analytical precision

Heterogeneities of both sample and source Range of measured values across a class

Number and independence of measured

parameters Contamination removal


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Annealing ScheduleStart temperature 25 CRamp rate 1 600 C/h

Level 1 555 C

Dwell time 1 2 h

Ramp rate 2 - 4 C/hLevel 2 500 C

Dwell time 2 10 min

Ramp rate 3 - 4 C/min

Level 3 25 C

W. Stoecklein, BKA


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Container RI homogeneity

1 2

3

4 56

7 8

910

Sample RI SD

1 1.52025 0.000102 1.52023 0.00004

3 1.52026 0.00003

4a 1.52036 0.00029

4b 1.52035 0.00023

5 1.52032 0.000066 1.52024 0.00009

7 1.52018 0.00005

8 1.52029 0.00012

9 1.52024 0.00005

10 1.52023 0.00009


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Characterization of glass sources

It is useful to determine 1) variation within asingle source and 2) variation within all sources

1) Within source studies (literature)(containers, float sheet, vehicle windows, headlamps)

2) Reference Databases

(FBI - RI and ICP-AES from casework,

FIU - RI and ICP-MS from surveys)


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Frequency Distribution (USA vs UK)

0.0000%

1.0000%

2.0000%

3.0000%

4.0000%

5.0000%

6.0000%

1.5

108

1.5

116

1.5

124

1.5

132

1.5

140

1.5

148

1.5

156

1.5

164

1.5

172

1.5

180

1.5

188

1.5

196

1.5

204

1.5

212

1.5

220

1.5

228

1.5

236

1.5

244

1.5

252

1.5

260

1.5

268

1.5

276

1.5

284

1.5

292

1.5

300

Refractive Index

%

Frequency

UK

USA

USA 1978-1990

UK 1977-1989


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Frequency Distribution (Dade vs USA)

0.000%

2.000%

4.000%

6.000%

8.000%

10.000%

12.000%

1.5126

1.5137

1.51

45

1.5153

1.5161

1.5169

1.5177

1.5185

1.5193

1.5201

1.5211

1.5219

1.5227

1.5235

1.52

43

1.5251

1.5259

Refractive Index

F

requency

Dade

USA

Dade 1990-1997

Headlamp Glass


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Headlamp Glass

Within and Between Distribution

Range of R.I. within one lamp (10 readings)

Lens Reflector.00020 units .00018 units

Range of R.I. between all lamps measured (73)

Lens Reflector Overall.00313 units .00326 units .00340 units

Minimum: 1.47604 Maximum: 1.47944

See: Ojena and DeForest, JFS, 1972


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?? Questions to Ponder ?? Does the measurement of dispersion increase

the discrimination capability over nD alone?

Does the measurement of density increase thediscrimination capability over nD alone?

Does the measurement of change in nD withannealing increase the discrimination capabilityover nD alone?

Are these all measures of the same thing?

Why was research initiated into the use of


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First, there was interest in classifying specimens

as to source to rule out or confirm alibis.

Later, there was concern that manufacturers had

improved their quality control and refractive indexwas not as discriminating as it had been

historically - greater discrimination power was

needed.

Why was research initiated into the use of

elemental analysis for glass in the 1980s?

Classification of Sheet and


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Classification of Sheet and

Container Glasses using %Mg

Magnesium (%)

0 1 2 3 4

No.ofS

amples

0

2

4

6

8

40

50

60

70

80

Containers

Sheets


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R e f r a c t iv e In d e x , n D

1.5

14

1.5

15

1.5

16

1.5

17

1.5

18

1.5

19

1.5

20

1.5

21

1.5

22

1.5

23

NumberofSamples

0

2

4

6

8

1 0

1 2

Refractive Indices of Auto Side Windows

Discrimination Potential of


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Coleman and Goode (1973) Used NAA looking at 25 elements

Were able to distinguish all but two pairsfrom 539 different glass samples

Al, As, Ba, Ca, Hf, Mn, Na, Rb, Sb, Sc,

and Sr provided the most discrimination


Elemental Composition Analysis



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Elemental Composition Analysis

38 of 40 windows were distinguished by EDX

Andrasko et al, JFS, 1977

25 of 28 windows were distinguished by SSMS

Haney, JFS, 1977

81 of 81 windows were distinguished by EDXReeve et al, JFS, 1976

78 of 81 vehicle windows were distinguished by ICP

Koons et al, J Analytical Atomic Spectrometry, 1991

Headlamps, Containers, Non-Vehicle and Vehicle

Documents

Module 3_Forensic Examinations