ASTM E1967-11a
(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 − 11a
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.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope glass.The temperature of the oil is changed via a hot stage and
an electronic temperature controller until the glass particles’
1.1 This test method covers a procedure for measuring the
t image disappears. The temperature at which there is minimum
refractive index (η ) of glass samples, irregularly shaped and
λ
contrast between the glass and the liquid then is recorded
assmallas300µg,forthecomparisonoffragmentsofaknown
manually or electronically.
source to recovered fragments from a questioned source.
2.2 A microprocessor or other handling station, such as a
1.2 This test method does not include the measurement of
t
personal computer, employs a video camera interfaced by
optical dispersion or the measurement of refractive index (η )
λ
t
at any other wavelength other than the Sodium D line (η ). appropriatesoftwareandhardwaretoviewtheglassfragments.
D
These commercial electronics result in a digital count repre-
This method employs a narrow band pass filter at 589 nm, but
otherfilterscouldbeemployedusingthedescribedmethodand senting a preselected edge feature’s contrast being determined.
t
allowing the η to be determined at other wavelengths, Thisedgeorcontrastmeasurementisupdatedwitheveryframe
λ
therefore, also allowing for the dispersion value to be calcu- ofvideoasthetemperatureofthehotstage,oil,andsampleare
lated. ramped up or down. The software automatically registers the
t
match point by taking the average of the minimum contrast
1.3 Alternative methods for the determination of η are
λ
2
measurementsforboththecoolingandtheheatingcycles.This
listed in Refs (1-5).
t
match temperature can be converted to η by reference to a
D
1.4 The values stated in SI units are to be regarded as
calibrationcurvefortheimmersionoilpreviouslycreatedfrom
standard. No other units of measurement are included in this
the match temperatures obtained on reference glass standards.
standard.
This calibration curve is obtained from reference glasses of
t,
1.5 This standard test method does not purport to address
known η s within the range of interest. This curve or its
D
all of the safety concerns, if any, associated with its use. It is
mathematical equivalent normally is stored within the micro-
t
the responsibility of the user to establish appropriate safety
processor and is employed to determine the η of any glass of
D
and health practices and determine the applicability of regu-
interest, whether it is a fragment of known origin or a
latory limitations prior to use.
recovered (questioned) fragment.
2.3 Precise control and measurement of the immersion
2. Summary of Test Method
liquid temperature is achieved by use of a microscope hot
2.1 A phase contrast microscope is employed with illumi-
stage. A precision of 0.05°C for the hot stage is desirable, but
nationatafixedwavelength(nominallySodiumD)tomagnify
a precision of 0.1°C is the requirement for interlaboratory
the image of glass particles while these are immersed in a
comparisons.
silicone oil. The microscope is aligned to produce even
illumination with maximum contrast and a video camera is
3. Significance and Use
attachedtoaneyepiece(theoutputoftheimage)toobservethe
immersed glass and measure the contrast of the image of the
3.1 This technique modifies the sample, in that the glass
fragmentmustbecrushed,ifitistoolarge,andimmersedinoil
for the analysis. Some sample handling, however, would
1
This practice is under the jurisdiction of ASTM Committee E30 on Forensic
enabletheanalysttorecoverthesampleinthecrushedform,if
Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.
necessary.
Current edition approved Dec. 1, 2011. Published December 2011. Originally
approved in 1998. Last previous edition approved in 2011 as E1967–11. DOI:
3.2 This test method is useful for accurate measurement of
10.1520/E1967-11A.
t
2
η fromawidevarietyofglasssamples,wheremostglassesof
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof D
t t
this standard. interest have η in the range between 1.48 – 1.55 in η units.
D D
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
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E1967 − 11a
3.3 The objective nature of the match point determination er
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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:E1967–11 Designation:E1967–11a
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 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
therefore, allows for the interchange of databases between laboratories.
1
This practice is under the jurisdiction of ASTM Committee E30 on Forensic Sciences and is the direc
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