GRIM-3
Definition
Glass Refractive Index Measurement, third-generation instrument by Foster + Freeman (UK); an automated phase-contrast hot-stage system that identifies the RI match point by curve-fitting the phase-contrast edge signal vs temperature, achieving ±0.00015 RI unit precision.
- Manufacturer
- Foster + Freeman Ltd (UK)
- Measurement method
- Automated phase-contrast microscopy with heated immersion-oil stage
- Typical precision
- 0.0001 to 0.00015 RI units
Common questions
What does GRIM-3 measure?+
GRIM-3 measures the refractive index of glass fragments using an automated hot-stage system. It identifies the exact RI value where a glass sample has the same light-bending properties as the surrounding immersion oil, which is the match point for forensic comparison.
How precise is GRIM-3?+
GRIM-3 achieves precision of about 0.0001 to 0.00015 refractive index units. This high precision allows forensic labs to distinguish between glass samples from different sources.
How does GRIM-3 work?+
The instrument uses automated phase-contrast microscopy with a heated immersion-oil stage. As temperature changes, the phase-contrast edge in the microscope shifts. GRIM-3 automatically curve-fits this signal against temperature to find the exact RI match point.
Related terms
- ASTM E1967
- The ASTM International standard for forensic glass RI measurement; specifies three acceptable methods (automated, semi-automated, manual), minimum precision of ±0.0001 RI units,...
- 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...
- 3R Rule
- The fracture-analysis mnemonic: Radial cracks form at Right angles to the Reverse (far, non-impact) side of the glass. Applied to the fracture...
- 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...
- Concentric Fracture
- An arc-shaped fracture encircling the impact zone, produced by outer-table bending tension at a distance from the focal impact; always post-dates the...
- Dispersion
- The variation of refractive index with wavelength; all glasses and immersion oils show dispersion, which is why RI must be specified at...
- Hackle Lines
- Fine secondary cracks on the fracture surface that fan from the origin, perpendicular to the moving crack front. Used to track crack...
- 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...
Explained in these topics
- Glass Comparison: RI, Density and LA-ICP-MSGlass Refractive Index Measurement instrument (Foster + Freeman Ltd, UK); uses automated phase-contrast microscopy with a heated immersion-oil stage to measure...
- Glass Evidence: Fracture Patterns and Refractive IndexGlass Refractive Index Measurement instrument, third generation. Hot-stage microscopy with sodium D-line illumination; reports RI to ±0.00002.
- Refractive Index: Becke Line, GRIM and Mettler Hot Stage