Metallographic etching is a laboratory technique for revealing the microstructure of metallic specimens. In this procedure, a chemical etching solution is applied to expose features like grain boundaries, phases, and defects.

Key features:

• Microstructural revelation: The etching process attacks different portions of the metal (usually the visible surface metal) and exposes previously invisible internal features.
• Types of etchants: Different metals have to be coupled with different etching solutions (for example, Nital for steel or Keller's reagent for aluminum) to effectively reveal the microstructural detail.
• Quality assessment: Metallographic etching reveals problems with the item because it reveals improper heat treatment, or it could reveal a defect or some impurity in manufacturing, or it could show a problem such as a crack or phase imbalance, and all of this information gives a person an assessment of the quality of the material.

Metallographic etching allows for additional information to be determined regarding the internal structure of a metal. Aerospace, automotive, and manufacturing companies rely on metallographic etching techniques to assess the materials being used and their performance, reliability, and optimization of manufacture. Knowledge can also be gained from metallographic etching techniques about the mechanical properties and whether a particular alloy advanced the desired properties. By determining grain size and phase distribution of an alloy system using metallographic etching techniques, engineers can assess increases, decreases, and shifts in alloy phase, structure, and properties.