ASTM_E_1967_-_11a.pdf

Designation:E196711aStandard 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 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 for 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 refractive 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 be calcu-lated.1.3 Alternative 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 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 Sodium 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 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 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 measurement 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 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 equivalent 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 hotstage.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 sample 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 under the jurisdiction of ASTM Committee E30 on ForensicSciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved Dec.1,2011.Published December 2011.Originallyapproved in 1998.Last previous edition approved in 2011 as E1967 11.DOI:10.1520/E1967-11A.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.3 The objective nature of the match point determinationallows for a better standardization 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 th