1、Designation:E196711 Designation: E1967 11aStandard 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
2、indicates 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers a procedure fo
3、r measuring the refractive index (hlt) of glass samples, irregularly shaped and assmall as 300 g, 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 refrac
4、tive index (hlt)atany other wavelength other than the Sodium D line (hDt). This method employs a narrow band pass filter at 589 nm, but other filterscould be employed using the described method and allowing the hltto be determined at other wavelengths, therefore, also allowingfor the dispersion valu
5、e to be calculated.1.3 Alternative methods for the determination of hltare listed in Refs (1-5).21.4 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 c
6、oncerns, if any, associated with its use. It is theresponsibility of the user to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Summary of Test Method2.1 A phase contrast microscope is employed with illumination at a fixed w
7、avelength (nominally Sodium D) to magnify theimage of glass particles while these are immersed in a silicone oil. The microscope is aligned to produce even illumination withmaximum contrast and a video camera is attached to an eyepiece (the output of the image) to observe the immersed glass andmeasu
8、re the contrast of the image of the glass. The temperature of the oil is changed via a hot stage and an electronic temperaturecontroller until the glass particles image disappears. The temperature at which there is minimum contrast between the glass andthe liquid then is recorded manually or electro
9、nically.2.2 A microprocessor or other handling station, such as a personal computer, employs a video camera interfaced by appropriatesoftware and hardware to view the glass fragments. These commercial electronics result in a digital count representing apreselected edge features contrast being determ
10、ined. This edge or contrast measurement is updated with every frame of video asthe temperature of the hot stage, oil, and sample are ramped up or down. The software automatically registers the match point bytaking the average of the minimum contrast measurements for both the cooling and the heating
11、cycles. This match temperature canbe converted to hDtby reference to a calibration curve for the immersion oil previously created from the match temperaturesobtained on reference glass standards. This calibration curve is obtained from reference glasses of known hDt,s within the rangeof interest. Th
12、is curve or its mathematical equivalent normally is stored within the microprocessor and is employed to determinethe hDtof any glass of interest, whether it is a fragment of known origin or a recovered (questioned) fragment.2.3 Precise control and measurement of the immersion liquid temperature is a
13、chieved by use of a microscope hot stage. Aprecision of 0.05C for the hot stage is desirable, but a precision of 0.1C is the requirement for interlaboratory comparisons.3. Significance and Use3.1 This technique modifies the sample, in that the glass fragment must be crushed, if it is too large, and
14、immersed in oil forthe analysis. Some sample handling, however, would enable the analyst to recover the sample in the crushed form, if necessary.3.2 This test method is useful for accurate measurement of hDtfrom a wide variety of glass samples, where most glasses ofinterest have hDtin the range betw
15、een 1.48 1.55 in hDtunits.3.3 The objective nature of the match point determination allows for a better standardization between laboratories, andtherefore, allows for the interchange of databases between laboratories.1This practice is under the jurisdiction of ASTM Committee E30 on Forensic Sciences
16、 and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved Sept.Dec. 1, 2011. Published OctoberDecember 2011. Originally approved in 1998. Last previous edition approved in 20032011 asE196798(2003).E1967 11. DOI: 10.1520/E1967-11A.2The boldface numbers in par
17、entheses refer to the list of references at the end of this standard.1This 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. Becauseit may not be technically possible to adequately depic
18、t all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 1942
19、8-2959, United States.3.4 It should be recognized that surface fragments, especially from float glass samples, can result in hDt,s measurably higherthan fragments from the bulk of the same source (5).3.5 The precision and bias of this test method should be established in each laboratory that employs
20、 it. Confidence intervals ora similar statistical quality statement should be quoted along with any reported hDtvalue. For instance, a laboratory may reportthat the error for the measurement, using a reference optical glass is 0.00003 units.3.6 It should be recognized that this technique measures th
21、e refractive index of the glass at the match point temperature, whichwill be higher than ambient temperature, and thus, may give different hDtvalues from those obtained by other methods, whichmeasure the refractive index at room temperature.4. Apparatus4.1 MicroscopeA microscope outfitted for phase
22、contrast and an appropriate objective (nominally 103 403) with a longworking distance condenser is employed.4.2 Temperature ControlA hot stage connected to a control device with a working range of approximately 26C to 118C,having a minimum precision of 0.1C is employed.34.3 ImagingA video camera is
23、required for the automated measurements and is mounted to an ocular or photography port ofthe microscope. The output from the camera is used for the image processing for automated match point determinations.4.4 IlluminationA narrow band interference filter is employed as a monochromatic source. For
24、Sodium D measurements 5896 5 nm with a band pass of 10 nm is appropriate. The intensity of the illumination is adjusted to give the brightest image possible,without overloading the video camera.4.5 Immersion OilsSilicone immersion oils having refractive indices within a specific range are required f
25、or the glasses understudy and are calibrated with the necessary standard reference glasses of known hDt.4.6 Standard Reference GlassesAminimum of three reference hDtare used, when possible, for the calibration of each siliconeoil to be used for the actual measurements.5. Procedure5.1 Prior to crushi
26、ng the glass sample for the hDtmeasurement, one should be certain that the possibility of obtaining a physicalmatch has been explored and other examinations requiring larger sample size, such as density have not been precluded.5.2 Arrange the microscope for optimum illumination and phase contrast. T
27、o insure maximum contrast, make sure the annularillumination ring from the condenser is aligned properly with the phase contrast shift plate, which is located within the objectiveby viewing the superimposition at the back focal plane of the objective. This alignment can be accomplished a number of w
28、ays,the most convenient of which is the use of Bertrandy lens or a phase centering telescope.5.3 Calibrate the necessary hDtoil from a set of three oils represented by oils of approximately 1.50, 1.53, and 1.55 usingreference glasses of known hDtto 6 0.00001. At least three glasses for each oil shou
29、ld be employed for the calibration. Oncecalibrated, the hDtof the oils can be plotted against the match temperatures to produce a calibration curve for each oil. Thepreprogrammed protocol within the automated system to perform this function can be used.5.4 After using an appropriate cleaning techniq
30、ue, such as a deionized water and alcohol rinse followed by drying, crush a smallfragment of the glass to be studied and deposit a small sample on a clean, flat microscope slide. Immerse this sample in the propersilicone oil and cover with a cover slip.5.5 Place the covered slide onto the hot stage
31、and focus the image. The phase ring alignment must be checked each time thata new preparation is made to ensure that the phase rings are in alignment.5.6 Vary the temperature by ramping up, or down, past the match point and then cooling down, or heating up, past the matchpoint. Record the match poin
32、t temperature in both directions and calculate the average. With microprocessor controlled units,recording will be performed automatically. The match point is that point at which the contrast is at a minimum, which correspondsto the disappearance of the edge of interest.5.7 Determine the hDtof the g
33、lass fragment measured by reading the hDtfrom the calibration curve (hDtversus matchtemperature) for the average match temperature. For the microprocessor-controlled units, this calculation is displayed and printedautomatically. The hDtvalue will represent the hDtof the sample at the match point tem
34、perature. To obtain the hDtat ambienttemperature the value must be corrected using the dn/dt for that glass. Note that this is not usually known for casework glasssamples. The match point temperature must be noted in the final report.5.8Repeat the analysis to determine the precision of the measureme
35、nt.5.8 Using the imaging and controller software, analyze localized portions (commonly referred to as “measurement windows”)of the entire image, for changes in refractive index. Place each measurement window across a portion of a focused glass edge andthe immersion oil. Begin the automated analysis,
36、 which will change the hot stage temperature in a controlled manner.Alternatively,record the video image of the heating and cooling cycles before setting the measurement windows. Record the match pointtemperatures for both cooling and heating cycles for each measurement window. The match point is th
37、at point at which the contrastis at a minimum, which corresponds to the disappearance of the edge of interest. Calculate the average of the heating and coolingmatch point temperatures of every measurement window separately.3Mettler Models FP502 and FP82 have been found satisfactory for this function
38、.E1967 11a26. Standards6.1 Check the system calibration periodically or prior to the performance of an analysis, as required.6.1.1 A separate reference glass (control) of known refractive index, distinct from that used for the calibration, for example,NIST, Schott, Locke, should be used to verify th
39、e calibration curve.6.2 Recalibrate the system any time that the control falls outside the acceptable parameters established by the laboratory oranalyst for this procedure.7. Precision and Bias7.1 PrecisionPrecision of refractive index measurements should meet the original equipment manufacturers sp
40、ecifications.Using a microprocessor-controlled instrument for the determination of the match point temperature, determine the standarddeviation of the refractive index measurements on a fragment of a glass standard by measuring one edge per measurement cyclerepeatedly for at least a five-hour period
41、. The precision is independent of both the accuracy of the temperature measurementand the characteristics of the silicone oil.7.2 BiasSince the measurement of the sample hDtis a direct comparison to the standard reference glasses used, no bias exists.Bias may be introduced in interlaboratory compari
42、sons due to the use of different standard reference glasses for calibration.8. Keywords8.1 glass comparisons; glass measurement; refractive indexREFERENCES(1) Miller, E.T., “Forensic Glass Comparisons,” Forensic Science Handbook, Saferstein, ed., Prentice Hall, Englewood Cliffs, NJ, 1982 , pp. 13918
43、3.(2) Association of Official Analytical Chemists Official Methods of Analysis (1990), “Characterization and Matching of Glass Fragments,” (973.65),pp.637639.(3) Precision of GRIM Reference: Canadian Society of Forensic Science, Vol 27, No. 3, 1994, pp. 203208.(4) Locke, J. “GRIMA Semi Automatic Dev
44、ice for Measuring the Refractive Index of Glass Particles,” The Microscope, Vol 35, 1987, pp. 151158.(5) Underhill, M., “Multiple Refractive Index in Float Glass,” JFSS, Vol 20, 1980, pp. 169176.ASTM International takes no position respecting the validity of any patent rights asserted in connection
45、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 such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible te
46、chnical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consider
47、ation at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr
48、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). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).E1967 11a3
