It happens with the best intentions. A component fails, someone wants to show the boss (or the investigator) a nice clear fracture, and out comes the wire brush, the solvent or the grit blaster. In one well-meant minute, evidence that took months or years to form is gone for good.
What the "dirt" actually is
A fracture surface is a recording. The material sitting on it is part of the recording:
- Oxide and corrosion-product thickness dates the crack. A fracture that has been open for years carries a different film to one that opened last Tuesday — and a crack whose origin is heavily oxidised while its final region is bright tells you it grew slowly, then finished fast.
- Deposit chemistry identifies the environment. Chlorides, sulphides, process residues and water-treatment chemicals on the surface distinguish mechanisms that look alike — for example, whether cracking was environmentally driven at all.
- Deposit distribution maps the sequence. Which regions were exposed to the environment, and for how long, reconstructs the order of events.
What cleaning destroys physically
Beyond the chemistry, mechanical cleaning damages the surface itself. Fractography reads fine features — beach marks, striations, dimples, cleavage facets, intergranular texture — at magnifications where a wire brush is a bulldozer. Even fingers leave corrosive residue on fresh steel; even refitting the two halves together bruises the mating features. Once these features are smeared, no laboratory can recover them.
"But it was covered in rust"
Investigators clean fracture surfaces too — but selectively, progressively and after documentation. The deposits are sampled and analysed first; then cleaning proceeds in gentle stages, examining and photographing between each. Controlled cleaning at the right point in the investigation is a technique. Cleaning at the point of failure discovery is destruction.
What to do instead
- Photograph the surface as found, with scale.
- Keep both halves apart — never fit them back together.
- Wrap in clean, dry material; keep dry.
- Note what has already touched the surface (hands, oil, water, weather).
- Send it as it is. Ugly evidence is good evidence.
The full first-day guide: what to preserve after a component failure →
When to contact MTIS
If a failure matters enough to investigate, contact us before anyone improves the evidence — we will tell you exactly what to protect for your specific case. And if the surface has already been cleaned, still call: the geometry, the microstructure and the history often carry enough to bound the answer, and we will be straight with you about the confidence that remains. How a failure investigation works →