1、Designation: E 1967 98 (REapproved 2003)Standard 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 E 1967; the number immediately following the designation i
2、ndicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers a procedure fo
3、r measuring therefractive 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 refractiv
4、e index (hlt)at any other 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
5、 be calcu-lated.1.3 Alternative methods for the determination of hltarelisted in Refs (1-5).21.4 This standard test method does not purport to addressall of the safety concerns, if any, associated with its use. It isthe responsibility of the user to establish appropriate safetyand health practices a
6、nd 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 Sodium D) to magnifythe image of glass particles while these are immersed in asilicone oil. The microscope i
7、s 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 of theglass. The temperature of the oil is changed via a hot stage andan electronic temperature contro
8、ller 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 other handling station, such as apersonal computer, employs a video camera interfaced byappropriate so
9、ftware 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 measurement is updated with every frameof video as the temperature of the hot stage, oil, and sample areram
10、ped 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 be converted to hDtby reference to acalibration curve for the immersion oil previously created fromthe
11、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 equivalent normally is stored within the micro-processor and is employed to determine the hDtof any glass ofint
12、erest, 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 hotstage. A precision of 0.05C for the hot stage is desirable, buta precision of 0.1C is the requirement for i
13、nterlaboratorycomparisons.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 sample handling, however, wouldenable the analyst to recover the sample in the crushed form, ifnecessary.3
14、.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.3.3 The objective nature of the match point determinationallows for a better standardization between laboratories, andthe
15、refore, allows for the interchange of databases betweenlaboratories.1This practice is under the jurisdiction of ASTM Committee E30 on ForensicSciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved Nov. 10, 1998. Published January 1999.2The boldfac
16、e 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.3.4 It should be recognized that surface fragments, espe-cially from float glass samples, can result
17、in hDt,s measurablyhigher than fragments from the bulk of the same source (5).3.5 The precision 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 i
18、nstance, alaboratory may report that the error for the measurement, usinga reference optical 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, maygiv
19、e different hDtvalues from those obtained by other methods,which measure the refractive 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 Con
20、trolA hot stage connected to a con-trol device with a working range of approximately 26C 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 c
21、amera is used for theimage processing for automated match point determinations.4.4 IlluminationA 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 giv
22、e thebrightest image possible, without overloading the video cam-era.4.5 Immersion OilsSilicone 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 Referenc
23、e GlassesA minimum of three ref-erence hDtare used, when possible, for the calibration of 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 be
24、en explored and other examinationsrequiring larger sample size, such as density have not 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 cont
25、rast shift plate, which is located withinthe objective by viewing the superimposition at 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 hDtoi
26、l from a set of three oilsrepresented by oils of approximately 1.50, 1.53, and 1.55 usingreference 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
27、 calibration curve for each oil.The preprogrammed protocol within the automated system toperform 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
28、smallsample on a clean, flat microscope slide. Immerse this samplein the proper silicone 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 ringsa
29、re in alignment.5.6 Vary the temperature by ramping up, or down, past thematch point and 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 automatical
30、ly.The match point is that point at which the contrast is at aminimum, which corresponds 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 the
31、microprocessor-controlled units, this calculation is displayedand printed automatically. 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 k
32、nown forcasework glass samples. The match point temperature must benoted in the final report.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 referenc
33、e glass (control) of known refrac-tive index, distinct from that used for the calibration, 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 analys
34、t for this procedure.7. Precision and Bias7.1 PrecisionUsing the microprocessor controlled deter-mination of the match point temperature, a standard deviationof 0.00002 hDtmay be expected on measurements of theseparate reference glass overa5hperiod. Over a five dayperiod, a standard deviation of 0.0
35、0003 hDtmay be expected.The precision is independent of both the accuracy of thetemperature measurement and the characteristics of the siliconeoil.7.2 BiasSince the measurement of the sample hDtis adirect comparison to the standard reference glasses used, no3Mettler Models FP502 and FP82 have been f
36、ound satisfactory for this function.E 1967 98 (REapproved 2003)2bias 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) Miller, E.T., “
37、Forensic Glass Comparisons,” Forensic Science Hand-book, 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), p.637639.(3) Precision of
38、 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,” JFSS, 1980,Vo
39、l 20, 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 infringement of
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42、 the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).E 1967 98 (REapproved 2003)3
