Definition
A controlled chemical process in which acid or another reactive solution is applied to the surface of a metal to remove a thin layer of material, expose grain structure, or prepare the surface for inspection, bonding, or finishing.
Plain English
Using a chemical (usually an acid) to eat away a small amount of metal from the surface, either to clean it, prepare it for paint or glue, or reveal cracks and flaws.
Context Anchor
Seen in aircraft maintenance instructions for preparing metal before painting, bonding, coating, or inspection.
Derivation
From the Dutch 'etsen' and German 'ätzen,' meaning 'to corrode' or 'to bite.' The idea is that the acid 'bites' into the metal, which is exactly what happens at the surface during the process.
Why Pilots Care
Etching is part of how aircraft surfaces are prepared for protective coatings and how technicians find hidden cracks during inspections. A pilot doesn't perform etching, but understanding it helps when reading maintenance records or discussing repairs with a mechanic.
Analogy
Etching is like lightly sanding a surface before painting, except the work is done by a chemical instead of sandpaper.
Intuition Check
Do not think of etch as simply scratching a surface. In aircraft maintenance, etching usually means controlled chemical action on the surface.
Example Sentence 1
The mechanic etched the aluminum panel with a mild acid solution before applying the primer.
Example Sentence 2
Etching the repaired fuselage panel ensured the new paint would adhere evenly and resist corrosion.