Definition
A method of judging the temper, or hardness, of steel by observing the color of the oxide film that forms on its polished surface as it is heated. As the steel rises in temperature, the oxide film passes through a predictable sequence of colors -- pale yellow, straw, brown, purple, blue -- each corresponding to a specific temperature. When the desired color appears, the steel is quenched to lock in that hardness.
Plain English
A way of telling how hard a piece of steel has become by watching the color that appears on its shiny surface as it heats up. Different colors mean different temperatures, and the worker cools the steel at the right color to get the hardness they want.
Context Anchor
Seen in aircraft maintenance and repair discussions involving heat treatment of steel parts or tools.
Derivation
Tempering comes from the Latin temperare, meaning to mix or moderate. In metalwork it means moderating the brittleness of hardened steel by reheating it. The 'color' part refers to the oxide colors used as a temperature gauge.
Why Pilots Care
Correct color tempering gives steel parts the right combination of hardness and toughness so they resist fatigue and cracking in flight-critical applications.
Grounding Statement
As steel is heated, its surface can change through visible colors, and those colors give a rough clue to how hot the steel has become.
Intuition Check
Color tempering does not mean painting a part or marking it with a color code. It means using the color caused by heating steel as a guide to its tempering temperature.
Example Sentence 1
The mechanic used color tempering to bring the screwdriver tip to a straw color before quenching it in oil.
Example Sentence 2
After grinding, the mechanic performed color tempering on the replacement bolt to restore its original toughness before reinstallation.