ASTM E1967
Definition
The ASTM International standard for forensic glass RI measurement; specifies three acceptable methods (automated, semi-automated, manual), minimum precision of ±0.0001 RI units, NIST-traceable calibration, and report content requirements.
- Standard body
- ASTM International
- Measurement target
- Refractive index of glass (precision: ±0.0001 RI units)
- Acceptable methods
- Automated, semi-automated, or manual measurement
Common questions
What is ASTM E1967 and why do forensic labs use it?+
ASTM E1967 is the standard test method for measuring refractive index in glass evidence during forensic analysis. Labs follow it because it specifies exactly how to calibrate equipment, replicate measurements, and report results, so glass comparisons are consistent and defensible across different labs and case work.
How precise is the refractive index measurement under ASTM E1967?+
The standard requires a minimum precision of plus or minus 0.0001 RI units. This tight tolerance means glass samples can be distinguished reliably when their refractive indices differ, which is crucial when matching evidence glass to a suspected source.
What methods are allowed for measuring glass RI under this standard?+
ASTM E1967 accepts three approaches: automated, semi-automated, and manual measurement. Whichever method a lab chooses must use NIST-traceable calibration and follow the standard's reporting requirements.
Related terms
- ENFSI ENG3-2013
- The ENFSI Glass Expert Working Group guideline for glass comparison casework; specifies the examination sequence, within-source variation requirements, statistical comparison framework, and...
- GRIM-3
- Glass Refractive Index Measurement, third-generation instrument by Foster + Freeman (UK); an automated phase-contrast hot-stage system that identifies the RI match point...
- ASTM E2927
- Standard test method for the determination of trace elements in glass samples using LA-ICP-MS; specifies the element suite, calibration standards (NIST SRM...
- Bayesian Likelihood Ratio
- A statistical framework for expressing the evidential value of a comparison: the ratio of the probability of the observed RI similarity given...
- Bayesian Likelihood Ratio (LR)
- The statistical framework that evaluates glass-fragment evidence by comparing the probability of the observed fragment population assuming contact with the source glass...
- Becke Line
- The bright optical halo at the edge of a solid fragment immersed in a liquid, visible under the microscope; moves toward the...
- Cauchy Equation
- The empirical equation n(λ) = A + B/λ² + C/λ⁴ that describes the wavelength dependence (dispersion) of a material's refractive index; used...
- Dispersion
- The variation of refractive index with wavelength; all glasses and immersion oils show dispersion, which is why RI must be specified at...
- Hotelling's T2
- The multivariate generalisation of the t-test used to compare mean element-concentration vectors between questioned and known glass populations; accounts for the full...
- Immersion Method
- The forensic technique of matching a glass fragment's RI to that of a reference oil by adjusting temperature; the fragment becomes invisible...
- LA-ICP-MS
- Laser ablation inductively coupled plasma mass spectrometry; a technique that fires a laser pulse at a sample surface, vaporises a tiny amount,...
- Locke 1985 Protocol
- The calibrated immersion-oil series and operational procedure for forensic glass RI measurement described by Locke and Underhill (1985); specifies the oil series,...
Explained in these topics
- Glass Comparison: RI, Density and LA-ICP-MSStandard test method for refractive index measurement of glass by automated phase-contrast microscopy; specifies calibration, replication, and reporting requir...
- Refractive Index: Becke Line, GRIM and Mettler Hot StageThe ASTM International standard for forensic glass RI measurement; specifies three acceptable methods (automated, semi-automated, manual), minimum precision of...