1、Designation: E1967 11Standard Test Method forthe Automated Determination of Refractive Index of GlassSamples Using the Oil Immersion Method and a PhaseContrast Microscope1This standard is issued under the fixed designation E1967; the number immediately following the designation indicates the year of
2、original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers a procedure for measuring therefrac
3、tive index (hlt) of glass samples, irregularly shaped andas small as 300 g, for the comparison of fragments of a knownsource to recovered fragments from a questioned source.1.2 This test method does not include the measurement ofoptical dispersion or the measurement of refractive index (hlt)at any o
4、ther wavelength other than the Sodium D line (hDt).This method employs a narrow band pass filter at 589 nm, butother filters could be employed using the described method andallowing the hltto be determined at other wavelengths,therefore, also allowing for the dispersion value to be calcu-lated.1.3 A
5、lternative methods for the determination of hltarelisted in Refs (1-5).21.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard test method does not purport to addressall of the safety concerns, if any, associated
6、with its use. It isthe responsibility of the user to establish appropriate safetyand health practices and determine the applicability of regu-latory limitations prior to use.2. Summary of Test Method2.1 A phase contrast microscope is employed with illumi-nation at a fixed wavelength (nominally Sodiu
7、m D) to magnifythe image of glass particles while these are immersed in asilicone oil. The microscope is aligned to produce evenillumination with maximum contrast and a video camera isattached to an eyepiece (the output of the image) to observe theimmersed glass and measure the contrast of the image
8、 of theglass. The temperature of the oil is changed via a hot stage andan electronic temperature controller until the glass particlesimage disappears. The temperature at which there is minimumcontrast between the glass and the liquid then is recordedmanually or electronically.2.2 A microprocessor or
9、 other handling station, such as apersonal computer, employs a video camera interfaced byappropriate software and hardware to view the glass fragments.These commercial electronics result in a digital count repre-senting a preselected edge features contrast being determined.This edge or contrast meas
10、urement is updated with every frameof video as the temperature of the hot stage, oil, and sample areramped up or down. The software automatically registers thematch point by taking the average of the minimum contrastmeasurements for both the cooling and the heating cycles. Thismatch temperature can
11、be converted to hDtby reference to acalibration curve for the immersion oil previously created fromthe match temperatures obtained on reference glass standards.This calibration curve is obtained from reference glasses ofknown hDt,s within the range of interest. This curve or itsmathematical equivale
12、nt normally is stored within the micro-processor and is employed to determine the hDtof any glass ofinterest, whether it is a fragment of known origin or arecovered (questioned) fragment.2.3 Precise control and measurement of the immersionliquid temperature is achieved by use of a microscope hotstag
13、e. A precision of 0.05C for the hot stage is desirable, buta precision of 0.1C is the requirement for interlaboratorycomparisons.3. Significance and Use3.1 This technique modifies the sample, in that the glassfragment must be crushed, if it is too large, and immersed in oilfor the analysis. Some sam
14、ple handling, however, wouldenable the analyst to recover the sample in the crushed form, ifnecessary.3.2 This test method is useful for accurate measurement ofhDtfrom a wide variety of glass samples, where most glassesof interest have hDtin the range between 1.48 1.55 in hDtunits.1This practice is
15、under the jurisdiction of ASTM Committee E30 on ForensicSciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved Sept. 1, 2011. Published October 2011. Originallyapproved in 1998. Last previous edition approved in 2003 as E1967 98 (2003).DOI: 10.152
16、0/E1967-11.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.3 The objective nature of the match point determinationallows for a better s
17、tandardization between laboratories, andtherefore, allows for the interchange of databases betweenlaboratories.3.4 It should be recognized that surface fragments, espe-cially from float glass samples, can result in hDt,s measurablyhigher than fragments from the bulk of the same source (5).3.5 The pr
18、ecision and bias of this test method should beestablished in each laboratory that employs it. Confidenceintervals or a similar statistical quality statement should bequoted along with any reported hDtvalue. For instance, alaboratory may report that the error for the measurement, usinga reference opt
19、ical glass is 0.00003 units.3.6 It should be recognized that this technique measures therefractive index of the glass at the match point temperature,which will be higher than ambient temperature, and thus, maygive different hDtvalues from those obtained by other methods,which measure the refractive
20、index at room temperature.4. Apparatus4.1 MicroscopeA microscope outfitted for phase contrastand an appropriate objective (nominally 103 403) with along working distance condenser is employed.4.2 Temperature ControlA hot stage connected to a con-trol device with a working range of approximately 26C
21、to118C, having a minimum precision of 0.1C is employed.34.3 ImagingA video camera is required for the automatedmeasurements and is mounted to an ocular or photography portof the microscope. The output from the camera is used for theimage processing for automated match point determinations.4.4 Illumi
22、nationA narrow band interference filter is em-ployed as a monochromatic source. For Sodium D measure-ments 589 6 5 nm with a band pass of 10 nm is appropriate.The intensity of the illumination is adjusted to give thebrightest image possible, without overloading the video cam-era.4.5 Immersion OilsSi
23、licone immersion oils having refrac-tive indices within a specific range are required for the glassesunder study and are calibrated with the necessary standardreference glasses of known hDt.4.6 Standard Reference GlassesA minimum of three ref-erence hDtare used, when possible, for the calibration of
24、 eachsilicone oil to be used for the actual measurements.5. Procedure5.1 Prior to crushing the glass sample for the hDtmeasure-ment, one should be certain that the possibility of obtaining aphysical match has been explored and other examinationsrequiring larger sample size, such as density have not
25、beenprecluded.5.2 Arrange the microscope for optimum illumination andphase contrast. To insure maximum contrast, make sure theannular illumination ring from the condenser is aligned prop-erly with the phase contrast shift plate, which is located withinthe objective by viewing the superimposition at
26、the back focalplane of the objective. This alignment can be accomplished anumber of ways, the most convenient of which is the use ofBertrandy lens or a phase centering telescope.5.3 Calibrate the necessary hDtoil from a set of three oilsrepresented by oils of approximately 1.50, 1.53, and 1.55 using
27、reference glasses of known hDtto 6 0.00001. At least threeglasses for each oil should be employed for the calibration.Once calibrated, the hDtof the oils can be plotted against thematch temperatures to produce a calibration curve for each oil.The preprogrammed protocol within the automated system to
28、perform this function can be used.5.4 After using an appropriate cleaning technique, such as adeionized water and alcohol rinse followed by drying, crush asmall fragment of the glass to be studied and deposit a smallsample on a clean, flat microscope slide. Immerse this samplein the proper silicone
29、oil and cover with a cover slip.5.5 Place the covered slide onto the hot stage and focus theimage. The phase ring alignment must be checked each timethat a new preparation is made to ensure that the phase ringsare in alignment.5.6 Vary the temperature by ramping up, or down, past thematch point and
30、then cooling down, or heating up, past thematch point. Record the match point temperature in bothdirections and calculate the average. With microprocessorcontrolled units, recording will be performed automatically.The match point is that point at which the contrast is at aminimum, which corresponds
31、to the disappearance of the edgeof interest.5.7 Determine the hDtof the glass fragment measured byreading the hDtfrom the calibration curve (hDtversus matchtemperature) for the average match temperature. For themicroprocessor-controlled units, this calculation is displayedand printed automatically.
32、The hDtvalue will represent the hDtof the sample at the match point temperature. To obtain the hDtat ambient temperature the value must be corrected using thedn/dt for that glass. Note that this is not usually known forcasework glass samples. The match point temperature must benoted in the final rep
33、ort.5.8 Repeat the analysis to determine the precision of themeasurement.6. Standards6.1 Check the system calibration periodically or prior to theperformance of an analysis, as required.6.1.1 A separate reference glass (control) of known refrac-tive index, distinct from that used for the calibration
34、, forexample, NIST, Schott, Locke, should be used to verify thecalibration curve.6.2 Recalibrate the system any time that the control fallsoutside the acceptable parameters established by the laboratoryor analyst for this procedure.7. Precision and Bias7.1 PrecisionPrecision of refractive index meas
35、urementsshould meet the original equipment manufacturers specifica-tions. Using a microprocessor-controlled instrument for thedetermination of the match point temperature, determine thestandard deviation of the refractive index measurements on afragment of a glass standard by measuring one edge perm
36、easurement cycle repeatedly for at least a five-hour3Mettler Models FP502 and FP82 have been found satisfactory for this function.E1967 112period. The precision is independent of both the accuracy of thetemperature measurement and the characteristics of the siliconeoil.7.2 BiasSince the measurement
37、of the sample hDtis adirect comparison to the standard reference glasses used, nobias exists. Bias may be introduced in interlaboratory compari-sons due to the use of different standard reference glasses forcalibration.8. Keywords8.1 glass comparisons; glass measurement; refractive indexREFERENCES(1
38、) Miller, E.T., “Forensic Glass Comparisons,” Forensic ScienceHandbook, Saferstein, ed., Prentice Hall, Englewood Cliffs, NJ, 1982,pp. 139183.(2) Association of Official Analytical Chemists Official Methods ofAnalysis (1990), “Characterization and Matching of Glass Frag-ments,” (973.65), pp.637639.(
39、3) Precision of GRIM Reference: Canadian Society of Forensic Science,Vol 27, No. 3, 1994, pp. 203208.(4) Locke, J. “GRIMA Semi Automatic Device for Measuring theRefractive Index of Glass Particles,” The Microscope, Vol 35, 1987,pp. 151158.(5) Underhill, M., “Multiple Refractive Index in Float Glass,
40、” JFSS,Vol20, 1980, pp. 169176.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof i
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