Non-Destructive Examination
Definition
Any examination that does not consume or significantly alter the stain: visual inspection, alternate light source (ALS) examination, photography, and microscopy of an intact surface. These are always performed before any chemical test.
- Examples
- Visual inspection, ALS, photography, microscopy
- Timing
- Always before any chemical test
- Field
- Biological stain examination, DNA preservation
Common questions
Why must non-destructive examination always precede chemical testing on a stain?+
Chemical tests consume or alter sample material and can interfere with downstream DNA recovery, so documenting appearance, presumptive screening under an alternate light source, and photography first preserves the maximum evidentiary value before any irreversible step.
Does presumptive chemical testing count as non-destructive?+
No, a presumptive test such as a colour test for blood applies a reagent to the sample and is treated as a separate, potentially sample-consuming step performed after the purely visual and optical non-destructive steps.
Related terms
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- Destructive Testing
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- Differential Extraction
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- PCR Inhibitor
- A co-extracted substance that interferes with Taq polymerase activity or primer annealing. Common inhibitors in forensic samples include haemoglobin (from blood on...
- Sequential Testing Protocol
- The standardised order in which biological stains are examined: presumptive test, then confirmatory test, then species confirmation, then typing and DNA analysis....