ASTM E1967-98
(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
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1.1 This test method covers a procedure for measuring the refractive index of glass samples, irregularly shaped and as small as 300 ug, 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 at any other wavelength other than the Sodium D line. This method employs a narrow band pass filter at 589 mm, but other filters could be employed using the described method and allowing the nx' to be determined at other wavelengths, therefore, also allowing for the dispersion value to be calculated.
1.3 Alternative methods for the determination of nx' are listed in Refs (1-5).
1.4 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E 1967 – 98
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 E 1967; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope appropriate software and hardware to view the glass fragments.
These commercial electronics result in a digital count repre-
1.1 This test method covers a procedure for measuring the
t
senting a preselected edge feature’s contrast being determined.
refractive index (h ) of glass samples, irregularly shaped and
l
This edge or contrast measurement is updated with every frame
as small as 300 μg, for the comparison of fragments of a known
of video as the temperature of the hot stage, oil, and sample are
source to recovered fragments from a questioned source.
ramped up or down. The software automatically registers the
1.2 This test method does not include the measurement of
t
match point by taking the average of the minimum contrast
optical dispersion or the measurement of refractive index (h )
l
t
measurements for both the cooling and the heating cycles. This
at any other wavelength other than the Sodium D line (h ).
D
t
match temperature can be converted to h by reference to a
D
This method employs a narrow band pass filter at 589 nm, but
calibration curve for the immersion oil previously created from
other filters could be employed using the described method and
t
the match temperatures obtained on reference glass standards.
allowing the h to be determined at other wavelengths,
l
This calibration curve is obtained from reference glasses of
therefore, also allowing for the dispersion value to be calcu-
t,
known h s within the range of interest. This curve or its
D
lated.
t
mathematical equivalent normally is stored within the micro-
1.3 Alternative methods for the determination of h are
l
t
processor and is employed to determine the h of any glass of
D
listed in Refs (1-5).
interest, whether it is a fragment of known origin or a
1.4 This standard test method does not purport to address
recovered (questioned) fragment.
all of the safety concerns, if any, associated with its use. It is
2.3 Precise control and measurement of the immersion
the responsibility of the user to establish appropriate safety
liquid temperature is achieved by use of a microscope hot
and health practices and determine the applicability of regu-
stage. A precision of 0.05°C for the hot stage is desirable, but
latory limitations prior to use.
a precision of 0.1°C is the requirement for interlaboratory
2. Summary of Test Method comparisons.
2.1 A phase contrast microscope is employed with illumi-
3. Significance and Use
nation at a fixed wavelength (nominally Sodium D) to magnify
3.1 This technique modifies the sample, in that the glass
the image of glass particles while these are immersed in a
fragment must be crushed, if it is too large, and immersed in oil
silicone oil. The microscope is aligned to produce even
for the analysis. Some sample handling, however, would
illumination with maximum contrast and a video camera is
enable the analyst to recover the sample in the crushed form, if
attached to an eyepiece (the output of the image) to observe the
necessary.
immersed glass and measure the contrast of the image of the
3.2 This test method is useful for accurate measurement of
glass. The temperature of the oil is changed via a hot stage and
t
h from a wide variety of glass samples, where most glasses
D
an electronic temperature controller until the glass particles’
t t
of interest have h in the range between 1.48 – 1.55 in h
image disappears. The temperature at which there is minimum D D
units.
contrast between the glass and the liquid then is recorded
3.3 The objective nature of the match point determination
manually or electronically.
allows for a better standardization between laboratories, and
2.2 A microprocessor or other handling station, such as a
therefore, allows for the interchange of databases between
personal computer, employs a video camera interfaced by
laboratories.
3.4 It should be recognized that surface fragments, espe-
t,
This practice is under the jurisdiction of ASTM Committee E-30 on Forensic
cially from float glass samples, can result in h s measurably
D
Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.
higher than fragments from the bulk of the same source (5).
Current edition approved Nov. 10, 1998. Published January 1999.
3.5 The precision and bias of this test method should be
The boldface numbers in parentheses refer to the list of references at the end of
this standard.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 1967
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 5.4 After using an appropriate cleaning technique, such as a
D
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 and focus the
t
give different h values from those obtained by other methods, image. The phase ring alignment must be checked each time
D
which measure the refractive index at room temperature. that a new preparation is made to ensure that the phase rings
are in alignment.
4. Apparatus
5.6 Vary the temperature by ramping up, or down, past the
4.1 Microscope—A microscope outfitted for phase contrast match point and then cooling down, or heating up, past the
and an appropriate objective (nom
...
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