ASTM E1967-19

Standard Test Method for the Automated Determination of Refractive Index of Glass Samples Using the Oil Immersion Method and a Phase Contrast Microscope

SIGNIFICANCE AND USE
4.1 This test method is useful for accurate measurement of  from a wide variety of glass samples, whose  ranges from 1.48–1.55.  
4.2 It should be recognized that measurement of surface fragments, especially from float glass samples, can result in refractive index values which are different than the refractive index values of fragments from the interior of (for example, bulk) the same broken glass source (5).  
4.3 The precision of this test method shall be established in each laboratory that employs it as part of the validation protocol (see Section 9).  
4.4 It should be recognized that this technique measures the refractive index of the glass at the match point temperature, which will be higher than ambient temperature, and thus, may give different  values from those obtained by other methods, which measure the refractive index at room temperature.
SCOPE
1.1 This test method covers a procedure for measuring and comparing the refractive index (η) at a fixed wavelength (λ) and temperature (T) ( ) of glass from known sources to recovered fragments from a questioned source.  
1.2 This test method does not include the measurement of optical dispersion or the measurement of refractive index ( ) at any other wavelength other than the Sodium D line ( ). This method employs a narrow band pass filter at 589 nm, but other filters could be employed using the described method, allowing the  to be determined at other wavelengths, and therefore, also allowing for the dispersion value to be calculated.  
1.3 Alternative methods for the determination of  are listed in Refs (1-5).2  
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.5 This standard cannot replace knowledge, skills, or abilities acquired through education, training, and experience and is to be used in conjunction with professional judgment by individuals with such discipline-specific knowledge, skills, and abilities.  
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Sep-2019
• ICS: 81.040.01 - Glass in general
• Technical Committee: E30 - Forensic Sciences
• Drafting Committee: E30.01 - Criminalistics

Relations

• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM E177-13 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2013
• Refers: ASTM E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2011
• Refers: ASTM E177-10 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Oct-2010
• Refers: ASTM E691-08 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Oct-2008
• Refers: ASTM E177-08 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Oct-2008
• Refers: ASTM E177-06b - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 15-Nov-2006
• Refers: ASTM E177-06a - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Nov-2006
• Refers: ASTM E691-05 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2005
• Refers: ASTM E177-04e1 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Nov-2004
• Refers: ASTM E177-04 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Nov-2004
• Refers: ASTM E177-06 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Nov-2004
• Refers: ASTM E177-90a(2002) - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 10-Jan-2002
• Refers: ASTM E691-99 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 10-May-1999

Overview

ASTM E1967-19: Standard Test Method for the Automated Determination of Refractive Index of Glass Samples Using the Oil Immersion Method and a Phase Contrast Microscope is a widely recognized international standard published by ASTM International. This test method sets forth procedures for the automated measurement and comparison of the refractive index (η) of glass fragments in forensic and materials science applications. The technique uses the oil immersion method and phase contrast microscopy to deliver accurate, reproducible results for glass samples across a refractive index range of 1.48–1.55, specifically at the sodium D line (589 nm).

ASTM E1967-19 is essential for professionals in forensic science, quality control, and materials analysis seeking standardized procedures to ensure reliable glass identification and comparison.

Key Topics

• Scope of Measurement: Measures and compares the refractive index of glass samples at a fixed wavelength (589 nm) and elevated temperature for match-point determination.
• Automated Oil Immersion Technique: Utilizes phase contrast microscopy and immersion oils calibrated against certified reference glasses, enabling precision and automation in refractive index assessment.
• Forensic Relevance: Designed for comparing known glass sources to fragments from questioned origins, supporting forensic investigations and legal proceedings.
• Precision and Quality Assurance: Laboratories must establish method precision as part of their validation protocols. The method includes recommendations for repeatability, reproducibility, and bias assessment.
• Sample Considerations: Recognizes that surface fragments may show different refractive indices from interior fragments, especially in float glass.
• Calibration and Standardization: Daily verification and calibration using reference glasses are required for consistent and accurate results.

Applications

• Forensic Glass Analysis: The standard is prominently used in forensic laboratories to compare glass evidence from crime scenes to glass from known sources, aiding investigations involving break-ins, vehicular incidents, and other cases where glass transfer may occur.
• Materials Identification and Quality Control: Applied within the glass manufacturing industry and research laboratories to verify the refractive index of glass products, ensuring material consistency and compliance with specifications.
• Research and Academic Study: Used as a reliable methodology in academic and research settings for studies involving glass properties and optical materials analysis.
• Regulatory and Legal Compliance: Provides a defensible and internationally recognized approach for glass comparison, supporting expert testimony and regulatory documentation.

Related Standards

• ASTM E177: Practice for Use of the Terms Precision and Bias in ASTM Test Methods.
• ASTM E691: Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method.
• Referenced Literature: Additional comparative methods and foundational research on glass refractive index measurement are cited in the standard for expanded study.

Keywords: Glass refractive index measurement, ASTM E1967-19, oil immersion method, phase contrast microscope, forensic glass comparison, optical properties of glass, quality control standards.

By adhering to ASTM E1967-19, organizations ensure credible, accurate, and reproducible refractive index measurements for glass samples, enhancing the quality and integrity of forensic and material science investigations.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1967 − 19 An American National Standard
Standard Test Method for
the Automated Determination of Refractive Index of Glass
Samples Using the Oil Immersion Method and a Phase
Contrast Microscope
This standard is issued under the fixed designation E1967; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.1 This test method covers a procedure for measuring and
comparing the refractive index (η) at a fixed wavelength (λ)
2. Referenced Documents
T
and temperature (T)(η ) of glass from known sources to
λ 3
2.1 ASTM Standards:
recovered fragments from a questioned source.
E177Practice for Use of the Terms Precision and Bias in
1.2 This test method does not include the measurement of
ASTM Test Methods
T
optical dispersion or the measurement of refractive index (η )
λ E691Practice for Conducting an Interlaboratory Study to
T
at any other wavelength other than the Sodium D line (η ).
D
Determine the Precision of a Test Method
This method employs a narrow band pass filter at 589 nm, but
3. Summary of Test Method
other filters could be employed using the described method,
T
allowing the η to be determined at other wavelengths, and
3.1 Oil immersion refractometry is used to determine the
λ
therefore, also allowing for the dispersion value to be calcu-
refractive index of glass fragments. The glass fragments are
lated.
mounted on a glass microscope slide in an immersion oil of
T
known refractive index over the temperature range of interest.
1.3 Alternative methods for the determination of η are
λ
The glass microscope slide is placed on a phase contrast
listed in Refs (1-5).
microscope mounted with a hot stage and a video camera.The
1.4 The values stated in SI units are to be regarded as
phase contrast microscope is employed with illumination at a
standard. No other units of measurement are included in this
fixed wavelength (nominally Sodium D) to magnify the image
standard.
of glass particles immersed in the silicone oil.The microscope
1.5 This standard cannot replace knowledge, skills, or
is aligned to produce even illumination with maximum con-
abilities acquired through education, training, and experience
trast. A video camera is attached to a photography port (the
and is to be used in conjunction with professional judgment by
output of the image) to observe the immersed glass and
individuals with such discipline-specific knowledge, skills, and
measure the contrast between the glass and the oil. The
abilities.
temperature of the oil is changed via the hot stage and an
electronic temperature controller until the glass particles’
1.6 This standard does not purport to address all of the
image disappears. The temperature of the oil at which there is
safety concerns, if any, associated with its use. It is the
minimum contrast between the glass and the liquid then is
responsibility of the user of this standard to establish appro-
recorded manually or electronically as the match temperature.
priate safety, health, and environmental practices and deter-
T
mine the applicability of regulatory limitations prior to use.
3.2 The match temperature is converted to η by reference
D
1.7 This international standard was developed in accor-
to a calibration curve for the immersion oil. This calibration
dance with internationally recognized principles on standard-
curve has been previously created by measuring the match
ization established in the Decision on Principles for the
temperatures of traceable reference glass standards of known
T
Development of International Standards, Guides and Recom-
η within the temperature range of interest. This curve or its
D
mathematical equivalent normally is stored within the com-
T
puter and used to determine the η of any glass of interest,
D
ThistestmethodisunderthejurisdictionofASTMCommitteeE30onForensic
whether it is a fragment of known origin or a recovered
Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.
Current edition approved Oct. 1, 2019. Published October 2019. Originally
approved in 1998. Last previous edition approved in 2011 as E1967–11a. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/E1967-19. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1967 − 19
(questioned) fragment. 5.6 Standard Reference Glasses—A minimum of three ref-
T
erence η are required to construct the calibration curve for
D
3.3 The refractive indices of recovered glass fragments are
each silicone oil used. When they are commercially available,
compared to a test interval defined by the range of refractive
three or more traceable reference glasses shall be used to
index measurements of a broken glass object (known) to
construct the calibration curve. In addition, a minimum of one
determineiftheycanbeexcludedasoriginatingfromthesame
reference glass (control) not used to construct the calibration
source.
curve is required to verify the calibration.
3.4 The glass sample is typically crushed prior refractive
5.7 Computer—Acomputerisrequiredthatisequippedwith
index analysis. The analyst shall examine the glass fragments
appropriatesoftwareandhardwaretoviewtheglassfragments,
for any potential fracture match before altering the physical
measure edge contrast, and record match temperatures.
characteristics of the sample. Some of the crushed glass
fragmentsareimmersedinsiliconeoil.Theglassfragmentsare
6. Procedure
recovered from the oil for sample preservation, as required.
6.1 Select a number of glass fragments from the known
4. Significance and Use
glass sample such that the variability in the refractive index
throughout the source can be assessed.
4.1 This test method is useful for accurate measurement of
T T
η fromawidevarietyofglasssamples,whose η rangesfrom
D D
6.2 A minimum of ten refractive index replicate measure-
1.48–1.55.
ments per known source for most non-tempered glass and
4.2 It should be recognized that measurement of surface twenty for most tempered glasses is recommended (6).
fragments, especially from float glass samples, can result in
6.3 Collect replicate measurements of the questioned glass
refractive index values which are different than the refractive
to insure that it is adequately characterized. A minimum of
index values of fragments from the interior of (for example,
three replicates is recommended for the comparison of the
bulk) the same broken glass source (5).
refractive index of glass (7).
4.3 The precision of this test method shall be established in
6.4 Arrange the microscope for optimum illumination and
each laboratory that employs it as part of the validation
phase contrast. To insure maximum contrast, make sure the
protocol (see Section 9).
annular illumination ring from the condenser is aligned prop-
4.4 It should be recognized that this technique measures the
erly with the phase contrast shift plate, which is located within
refractive index of the glass at the match point temperature,
the objective. The rings are imaged on the back focal plane of
which will be higher than ambient temperature, and thus, may
the objective and can be observed in a number of ways, the
T
give different η values from those obtained by other methods,
mostconvenientofwhichistheuseofBertrandlensoraphase
D
which measure the refractive index at room temperature.
centering telescope.
T
6.5 Calibrate the necessary η oil as indicated in 7.3.
D
5. Apparatus
6.6 After using an appropriate cleaning technique, such as a
5.1 Microscope—A microscope outfitted for phase contrast
deionized water and alcohol rinse followed by drying, crush a
andanappropriatelongworkingdistanceobjective(nominally
small fragment of the glass to be measured and deposit a small
10–40×) is required.
sampleonacleanmicroscopeslide.Immersethissampleinthe
5.2 Temperature Control—A hot stage is required that con-
proper calibrated silicone oil and cover with a cover slip.
nects to a control device with a working range of approxi-
6.7 Place the covered slide onto the hot stage and focus the
mately 26°C to 118°C, having a minimum precision of 0.1°C.
image. The phase ring alignment shall be checked each time
5.3 Imaging—A digital video camera is required for the
that a new slide preparation is inserted into the hot stage to
automated measurements and is mounted to an ocular or
ensure that the phase rings are in alignment.
photography port of the microscope. The output from the
6.8 Tominimizeanalysistime,setthetemperatureofthehot
camera (image) is used for automated match point determina-
stagetowithinseveraldegreesoftheestimatedmatchpoint.To
tions.
estimatethematchpointofaglass,varythetemperatureofthe
5.4 Illumination—A narrow band interference filter is re-
hotstageeitherupordownasappropriateuntilthematchpoint
quired. For Sodium D measurements 589 6 5 nm with a band
has been reached and passed. The match point is that point at
pass of 10 nm is appropriate. The intensity of the illumination
which the contrast is at a minimum, which corresponds to the
is adjusted to give the brightest image possible, without
disappearance of the edge of interest. With computer-
overloading the video camera.
controlled units, the match point will be recorded automati-
5.5 Immersion Oils—Siliconeimmersionoilshavingrefrac-
cally.
tive indices within a specific range are required and are
6.9 Using the imaging and controller software, analyze
calibrated with the necessary standard reference glasses of
localized portions (commonly referred to as “measurement
T
known η .
D
windows”) of the edge of the glass for changes in refractive
index. Place each measurement window across a portion of a
focusedglassedgeandtheimmersionoil.Begintheautomated
MettlerModelsFP502andHS82havebeenfoundsatisfactoryforthisfunction.
Other similar brands/models can be used. analysis, which will change the hot stage temperature in a
E1967 − 19
controlledmanner.Alternatively,recordthevideoimageofthe
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E1967 − 11a E1967 − 19
Standard Test Method for
the Automated Determination of Refractive Index of Glass
Samples Using the Oil Immersion Method and a Phase
Contrast Microscope
This standard is issued under the fixed designation E1967; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
t
1.1 This test method covers a procedure for measuring and comparing the refractive index (η(η) ) of glass samples, irregularly
λ
T
shaped and as small at a fixed wavelength (λ) and temperature (T as) (η 300 μg, for the comparison of fragments of a known
λ
source) of glass from known sources to recovered fragments from a questioned source.
t
T
1.2 This test method does not include the measurement of optical dispersion or the measurement of refractive index (η( η ) at
λ λ
t
T
any other wavelength other than the Sodium D line (η( η ). This method employs a narrow band pass filter at 589 nm, but other
D
D
t
T
filters could be employed using the described method and method, allowing the ηη to be determined at other wavelengths, and
λλ
therefore, also allowing for the dispersion value to be calculated.
t 2
T
1.3 Alternative methods for the determination of ηη are listed in Refs (1-5).
λλ
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 This standard cannot replace knowledge, skills, or abilities acquired through education, training, and experience and is to
be used in conjunction with professional judgment by individuals with such discipline-specific knowledge, skills, and abilities.
1.6 This standard test method does not purport to address all of the safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and
determine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Summary of Test Method
3.1 A Oil immersion refractometry is used to determine the refractive index of glass fragments. The glass fragments are
mounted on a glass microscope slide in an immersion oil of known refractive index over the temperature range of interest. The
glass microscope slide is placed on a phase contrast microscope mounted with a hot stage and a video camera. The phase contrast
microscope is employed with illumination at a fixed wavelength (nominally Sodium D) to magnify the image of glass particles
while these are immersed in athe silicone oil. The microscope is aligned to produce even illumination with maximum contrast and
a contrast. A video camera is attached to an eyepiece a photography port (the output of the image) to observe the immersed glass
and measure the contrast ofbetween the image ofglass and the glass.oil. The temperature of the oil is changed via athe hot stage
This practice test method is under the jurisdiction of ASTM Committee E30 on Forensic Sciences and is the direct responsibility of Subcommittee E30.01 on
Criminalistics.
Current edition approved Dec. 1, 2011Oct. 1, 2019. Published December 2011October 2019. Originally approved in 1998. Last previous edition approved in 2011 as
E1967 – 11.E1967 – 11a. DOI: 10.1520/E1967-11A.10.1520/E1967-19.
The boldface numbers in parentheses refer to the list of references at the end of this standard.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1967 − 19
and an electronic temperature controller until the glass particles’ image disappears. The temperature of the oil at which there is
minimum contrast between the glass and the liquid then is recorded manually or electronically.electronically as the match
temperature.
3.2 A microprocessor or other handling station, such as a personal computer, employs a video camera interfaced by appropriate
software and hardware to view the glass fragments. These commercial electronics result in a digital count representing a
preselected edge feature’s contrast being determined. This edge or contrast measurement is updated with every frame of video as
the temperature of the hot stage, oil, and sample are ramped up or down. The software automatically registers the match point by
taking the average of the minimum contrast measurements for both the cooling and the heating cycles. This match temperature can
t
T
be converted to ηThe match temperature is converted to η by reference to a calibration curve for the immersion oil previously
DD
created from the match temperatures obtained on reference glass standards. oil. This calibration curve is obtained from reference
glasses of known ηhas been previously created by measuring the match temperatures of traceable reference glass standards of
t,
T
known η s within the temperature range of interest. This curve or its mathematical equivalent normally is stored within the
DD
t
T
microprocessorcomputer and is employed used to determine the ηη of any glass of interest, whether it is a fragment of known
DD
origin or a recovered (questioned) fragment.
3.3 The refractive indices of recovered glass fragments are compared to a test interval defined by the range of refractive index
measurements of a broken glass object (known) to determine if they can be excluded as originating from the same source.
3.4 Precise control and measurement of the immersion liquid temperature is achieved by use of a microscope hot stage. A
precision of 0.05°C for the hot stage is desirable, but a precision of 0.1°C is the requirement for interlaboratory comparisons.The
glass sample is typically crushed prior refractive index analysis. The analyst shall examine the glass fragments for any potential
fracture match before altering the physical characteristics of the sample. Some of the crushed glass fragments are immersed in
silicone oil. The glass fragments are recovered from the oil for sample preservation, as required.
4. Significance and Use
3.1 This technique modifies the sample, in that the glass fragment must be crushed, if it is too large, and immersed in oil for
the analysis. Some sample handling, however, would enable the analyst to recover the sample in the crushed form, if necessary.
t
T T
4.1 This test method is useful for accurate measurement of ηη from a wide variety of glass samples, where mostwhose η
D D
D
t t
glasses of interest have ηranges from 1.48–1.55. in the range between 1.48 – 1.55 in η units.
D D
3.3 The objective nature of the match point determination allows for a better standardization between laboratories, and
therefore, allows for the interchange of databases between laboratories.
4.2 It should be recognized that measurement of surface fragments, especially from float glass samples, can result in
t,
ηrefractive s measurably higher than index values which are different than the refractive index values of fragments from the bulk
D
of interior of (for example, bulk) the same broken glass source ((5).).
4.3 The precision and bias of this test method shouldshall be established in each laboratory that employs it. Confidence intervals
t
or a similar statistical quality statement should be quoted along with any reported ηit as part of value. For instance, a laboratory
D
may report that the error for the measurement,the validation protocol (see Section 9using a reference optical glass is 0.00003
units.).
4.4 It should be recognized that this technique measures the refractive index of the glass at the match point temperature, which
t
T
will be higher than ambient temperature, and thus, may give different ηη values from those obtained by other methods, which
DD
measure the refractive index at room temperature.
5. Apparatus
5.1 Microscope—A microscope outfitted for phase contrast and an appropriate objective (nominally 10× – 40×) with a long
working distance condenser is employed.objective (nominally 10–40×) is required.
5.2 Temperature Control—A hot stage connected is required that connects to a control device with a working range of
approximately 26°C to 118°C, having a minimum precision of 0.1°C is employed.0.1°C.
5.3 Imaging—A digital video camera is required for the automated measurements and is mounted to an ocular or photography
port of the microscope. The output from the camera (image) is used for the image processing for automated match point
determinations.
5.4 Illumination—A narrow band interference filter is employed as a monochromatic source. required. For Sodium D
measurements 589 6 5 nm with a band pass of 10 nm is appropriate. The intensity of the illumination is adjusted to give the
brightest image possible, without overloading the video camera.
5.5 Immersion Oils—Silicone immersion oils having refractive indices within a specific range are required for the glasses under
Mettler Models FP502 and FP82HS82 have been found satisfactory for this function. Other similar brands/models can be used.
E1967 − 19
t
T
study and are calibrated with the necessary standard reference glasses of known ηη .
DD
t
T
5.6 Standard Reference Glasses—A minimum of three reference ηη are used, when possible, for required to construct the
DD
calibration of curve for each silicone oil to be used for the actual measurements.used. When they are commercially available, three
or more traceable reference glasses shall be used to construct the calibration curve. In addition, a minimum of one reference glass
(control) not used to construct the calibration curve is required to verify the calibration.
5.7 Computer—A computer is required that is equipped with appropriate software and hardware to view the glass fragments,
measure edge contrast, and record match temperatures.
6. Procedure
t
6.1 Prior to crushing the glass sample for the ηSelect a number of glass fragments from the known glass sample such
D
measurement, one should be certain that the possibility of obtaining a physical match has been explored and other examinations
requiring larger sample size, such as density have not been precluded.that the variability in the refractive index throughout the
source can be assessed.
6.2 A minimum of ten refractive index replicate measurements per known source for most non-tempered glass and twenty for
most tempered glasses is recommended (6).
6.3 Collect replicate measurements of the questioned glass to insure that it is adequately characterized. A minimum of three
replicates is recommended for the comparison of the refractive index of glass (7).
6.4 Arrange the microscope for optimum illumination and phase contrast. To insure maximum contrast, make sure the annular
illumination ring from the condenser is aligned properly with the phase contrast shift plate, which is located within the objective
by viewing the superimposition atobjective. The rings are imaged on the back focal plane of the objective. This alignment objective
and can be accomplished observed in a number of ways, the most convenient of which is the use of Bertrand™Bertrand lens or
a phase centering telescope.
t
T
6.5 Calibrate the necessary ηη oil from a setas indicated in 7.3of three oils represented by oils of approximately 1.50, 1.53,
DD
t
and 1.55 using reference glasses of known η. to 6 0.00001. At least three glasses for each oil should be employed for the
D
t
calibration. Once calibrated, the η of the oils can be plotted against the match temperatures to produce a calibration curve for
D
each oil. The preprogrammed protocol within the automated system to perform this function can be used.
6.6 After using an appropriate cleaning technique, such as a deionized water and alcohol rinse followed by drying, crush a small
fragment of the glass to be studiedmeasured and deposit a small sample on a clean, flat clean microscope slide. Immerse this
sample in the proper calibrated silicone oil and cover with a cover slip.
6.7 Place the covered slide onto the hot stage and focus the image. The phase ring alignment mustshall be checked each time
that a new slide preparation is made inserted into the hot stage to ensure that the phase rings are in alignment.
6.8 Vary the temperature by ramping up, or down, past the match point and then cooling down, or heating up, past the match
point. Record To minimize analysis time, set the temperature of the hot stage to within several degrees of the estimated match
point. To estimate the match point temperature in both directions and calculate the average. With micro
...