ASTM E1967-11
(Test Method)Standard Test Method for the Automated Determination of Refractive Index of Glass Samples Using the Oil Immersion Method and a Phase Contrast Microscope
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
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.
This test method is useful for accurate measurement of ηDt from a wide variety of glass samples, where most glasses of interest have ηDt in the range between 1.48 – 1.55 in ηDt units.
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.
It should be recognized that surface fragments, especially from float glass samples, can result in ηDt,s measurably higher than fragments from the bulk of the same source (5).
The precision and bias of this test method should be established in each laboratory that employs it. Confidence intervals or a similar statistical quality statement should be quoted along with any reported ηDt value. For instance, a laboratory may report that the error for the measurement, using a reference optical glass is 0.00003 units.
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 ηDt 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 the refractive index (ηλt) of glass samples, irregularly shaped and as small as 300 μg, for the comparison of fragments of a known source 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 (ηλt) at any other wavelength other than the Sodium D line (ηDt). This method employs a narrow band pass filter at 589 nm, but other filters could be employed using the described method and allowing the ηλt to be determined at other wavelengths, therefore, also allowing for the dispersion value to be calculated.
1.3 Alternative methods for the determination of ηλt are listed in Refs (1-5).
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 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 to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:E1967–11
Standard Test Method for
the Automated Determination of Refractive Index of Glass
Samples Using the Oil Immersion Method and a Phase
1
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 an electronic temperature controller until the glass particles’
image disappears. The temperature at which there is minimum
1.1 This test method covers a procedure for measuring the
t
contrast between the glass and the liquid then is recorded
refractive index (h ) of glass samples, irregularly shaped and
l
manually or electronically.
assmallas300µg,forthecomparisonoffragmentsofaknown
2.2 A microprocessor or other handling station, such as a
source to recovered fragments from a questioned source.
personal computer, employs a video camera interfaced by
1.2 This test method does not include the measurement of
t
appropriatesoftwareandhardwaretoviewtheglassfragments.
optical dispersion or the measurement of refractive index (h )
l
t
These commercial electronics result in a digital count repre-
at any other wavelength other than the Sodium D line (h ).
D
senting a preselected edge feature’s contrast being determined.
This method employs a narrow band pass filter at 589 nm, but
Thisedgeorcontrastmeasurementisupdatedwitheveryframe
otherfilterscouldbeemployedusingthedescribedmethodand
t
of video as the temperature of the hot stage, oil, and sample are
allowing the h to be determined at other wavelengths,
l
ramped up or down. The software automatically registers the
therefore, also allowing for the dispersion value to be calcu-
match point by taking the average of the minimum contrast
lated.
t
measurements for both the cooling and the heating cycles.This
1.3 Alternative methods for the determination of h are
l
t
2
match temperature can be converted to h by reference to a
D
listed in Refs (1-5).
calibration curve for the immersion oil previously created from
1.4 The values stated in SI units are to be regarded as
the match temperatures obtained on reference glass standards.
standard. No other units of measurement are included in this
This calibration curve is obtained from reference glasses of
standard.
t,
known h s within the range of interest. This curve or its
1.5 This standard test method does not purport to address D
mathematical equivalent normally is stored within the micro-
all of the safety concerns, if any, associated with its use. It is
t
processor and is employed to determine the h of any glass of
the responsibility of the user to establish appropriate safety D
interest, whether it is a fragment of known origin or a
and health practices and determine the applicability of regu-
recovered (questioned) fragment.
latory limitations prior to use.
2.3 Precise control and measurement of the immersion
2. Summary of Test Method liquid temperature is achieved by use of a microscope hot
stage. A precision of 0.05°C for the hot stage is desirable, but
2.1 A phase contrast microscope is employed with illumi-
a precision of 0.1°C is the requirement for interlaboratory
nation at a fixed wavelength (nominally Sodium D) to magnify
comparisons.
the image of glass particles while these are immersed in a
silicone oil. The microscope is aligned to produce even
3. Significance and Use
illumination with maximum contrast and a video camera is
3.1 This technique modifies the sample, in that the glass
attached to an eyepiece (the output of the image) to observe the
fragmentmustbecrushed,ifitistoolarge,andimmersedinoil
immersed glass and measure the contrast of the image of the
for the analysis. Some sample handling, however, would
glass. The temperature of the oil is changed via a hot stage and
enable the analyst to recover the sample in the crushed form, if
necessary.
1
This practice is under the jurisdiction of ASTM Committee E30 on Forensic
3.2 This test method is useful for accurate measurement of
Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics. t
h from a wide variety of glass samples, where most glasses
D
Current edition approved Sept. 1, 2011. Published October 2011. Originally
t t
of interest have h in the range between 1.48 – 1.55 in h
approved in 1998. Last previous edition approved in 2003 as E1967 – 98 (2003). D D
DOI: 10.1520/E1967-11. units.
2
The boldface numbers in parentheses refer to the list of references at the end of
this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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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:E1967–98(Reapproved2003) Designation:E1967–11
Standard Test Method for
the Automated Determination of Refractive Index of Glass
Samples Using the Oil Immersion Method and a Phase
1
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 the refractive index (h ) of glass samples, irregularly shaped and as
l
small as 300 µg, for the comparison of fragments of a known source to recovered fragments from a questioned source.
t
1.2 This test method does not include the measurement of optical dispersion or the measurement of refractive index (h )at
l
t
anyotherwavelengthotherthantheSodiumDline(h ).Thismethodemploysanarrowbandpassfilterat589nm,butotherfilters
D
t
couldbeemployedusingthedescribedmethodandallowingthe h tobedeterminedatotherwavelengths,therefore,alsoallowing
l
for the dispersion value to be calculated.
t
2
1.3 Alternative methods for the determination of h are listed in Refs (1-5).
l
1.4
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 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 to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Summary of Test Method
2.1 A 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 a silicone oil. The microscope is aligned to produce even illumination with
maximum contrast and a video camera is attached to an eyepiece (the output of the image) to observe the immersed glass and
measure the contrast of the image of the glass. The temperature of the oil is changed via a hot stage and an electronic temperature
controller until the glass particles’ image disappears. The temperature at which there is minimum contrast between the glass and
the liquid then is recorded manually or electronically.
2.2 Amicroprocessor 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
be converted to h by reference to a calibration curve for the immersion oil previously created from the match temperatures
D
t,
obtained on reference glass standards. This calibration curve is obtained from reference glasses of known h s within the range
D
of interest. This curve or its mathematical equivalent normally is stored within the microprocessor and is employed to determine
t
the h of any glass of interest, whether it is a fragment of known origin or a recovered (questioned) fragment.
D
2.3 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.
3. 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
3.2 This test method is useful for accurate measurement of h from a wide variety of glass samples, where most glasses of
D
t t
interest have h in the range between 1.48 – 1.55 in h units.
D D
3.3 The objective nature of the match point determination allows for a better standardization between laboratories, and
1
This practice is under the jurisdiction of ASTM Committee E30 on Forensic Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalist
...
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