ASTM E1967-98(2003)
(Test Method)Standard Test Method for the Automated Determinaton of Refractive Index of Glass Samples Using the Oil Immersion Method and a Phase Contrast Microscope
Standard Test Method for the Automated Determinaton 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 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:E1967–98(Reapproved2003)
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 image disappears. The temperature at which there is minimum
contrast between the glass and the liquid then is recorded
1.1 This test method covers a procedure for measuring the
t
manually or electronically.
refractive index (h ) of glass samples, irregularly shaped and
l
2.2 A microprocessor or other handling station, such as a
assmallas300µg,forthecomparisonoffragmentsofaknown
personal computer, employs a video camera interfaced by
source to recovered fragments from a questioned source.
appropriatesoftwareandhardwaretoviewtheglassfragments.
1.2 This test method does not include the measurement of
t
These commercial electronics result in a digital count repre-
optical dispersion or the measurement of refractive index (h )
l
t
senting a preselected edge feature’s contrast being determined.
at any other wavelength other than the Sodium D line (h ).
D
Thisedgeorcontrastmeasurementisupdatedwitheveryframe
This method employs a narrow band pass filter at 589 nm, but
of video as the temperature of the hot stage, oil, and sample are
other filters could be employed using the described method and
t
ramped up or down. The software automatically registers the
allowing the h to be determined at other wavelengths,
l
match point by taking the average of the minimum contrast
therefore, also allowing for the dispersion value to be calcu-
measurements for both the cooling and the heating cycles.This
lated.
t
t
match temperature can be converted to h by reference to a
D
1.3 Alternative methods for the determination of h are
l
calibration curve for the immersion oil previously created from
listed in Refs (1-5).
the match temperatures obtained on reference glass standards.
1.4 This standard test method does not purport to address
This calibration curve is obtained from reference glasses of
all of the safety concerns, if any, associated with its use. It is
t,
known h s within the range of interest. This curve or its
D
the responsibility of the user to establish appropriate safety
mathematical equivalent normally is stored within the micro-
and health practices and determine the applicability of regu-
t
processor and is employed to determine the h of any glass of
D
latory limitations prior to use.
interest, whether it is a fragment of known origin or a
2. Summary of Test Method
recovered (questioned) fragment.
2.3 Precise control and measurement of the immersion
2.1 A phase contrast microscope is employed with illumi-
liquid temperature is achieved by use of a microscope hot
nation at a fixed wavelength (nominally Sodium D) to magnify
stage. A precision of 0.05°C for the hot stage is desirable, but
the image of glass particles while these are immersed in a
a precision of 0.1°C is the requirement for interlaboratory
silicone oil. The microscope is aligned to produce even
comparisons.
illumination with maximum contrast and a video camera is
attached to an eyepiece (the output of the image) to observe the
3. Significance and Use
immersed glass and measure the contrast of the image of the
3.1 This technique modifies the sample, in that the glass
glass. The temperature of the oil is changed via a hot stage and
fragmentmustbecrushed,ifitistoolarge,andimmersedinoil
an electronic temperature controller until the glass particles’
for the analysis. Some sample handling, however, would
enable the analyst to recover the sample in the crushed form, if
This practice is under the jurisdiction of ASTM Committee E30 on Forensic
necessary.
Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.
3.2 This test method is useful for accurate measurement of
Current edition approved Nov. 1, 2003. Published December 2003. Originally
t
h from a wide variety of glass samples, where most glasses
approved in 1998. Last previous edition approved in 1998 as E1967 – 98. DOI: D
t t
10.1520/E1967-98R03.
of interest have h in the range between 1.48 – 1.55 in h
D D
The boldface numbers in parentheses refer to the list of references at the end of
units.
this standard.
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E1967–98 (2003)
3.3 The objective nature of the match point determination number of ways, the most convenient of which is the use of
allows for a better standardization between laboratories, and Bertrandy lens or a phase centering telescope.
t
therefore, allows for the interchange of databases between
5.3 Calibrate the necessary h oil from a set of three oils
D
laboratories.
represented by oils of approximately 1.50, 1.53, and 1.55 using
t
3.4 It should be recognized that surface fragments, espe-
reference glasses of known h to 6 0.00001. At least three
D
t,
cially from float glass samples, can result in h s measurably
glasses for each oil should be employed for the calibration.
D
t
higher than fragments from the bulk of the same source (5).
Once calibrated, the h of the oils can be plotted against the
D
3.5 The precision and bias of this test method should be
match temperatures to produce a calibration curve for each oil.
established in each laboratory that employs it. Confidence
The preprogrammed protocol within the automated system to
intervals or a similar statistical quality statement should be
perform this function can be used.
t
quoted along with any reported h value. For instance, a
D
5.4 After using an appropriate cleaning technique, such as a
laboratory may report that the error for the measurement, using
deionized water and alcohol rinse followed by drying, crush a
a reference optical glass is 0.00003 units.
small fragment of the glass to be studied and deposit a small
3.6 It should be recognized that this technique measures the
sample on a clean, flat microscope slide. Immerse this sample
refractive index of the glass at the match point temperature,
in the proper silicone oil and cover with a cover slip.
which will be higher than ambient temperature, and thus, may
5.5 Place the covered slide onto the hot stage
...
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