How to Heat-Treat Metal Colors
Aluminum, bronze, and a copper alloy called spring copper of beryllium copper can all be heat-treated using special processes including gas quenching and vacuum heating. But, heat-treating is usually done to steel. Most of the technique for hardening, tempering and combining steels is thousands of years old and some of the craft has been forgotten. So today nobody knows exactly how swords that were both flexible and razor sharp were made in medieval Japan. What is known is that those early metallurgists perfected their craft using colors anyone can see rather than laboratory tests.
Things You'll Need
- Piece of steel
- Vise-grips
- Propane torch
- Match
- Leather work gloves
- Anvil
- 5-gallon bucket
- 4 gallons vegetable oil
Instructions
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Secure a piece of steel in a pair of vise-grips. Hold the metal in the vise-grips so the metal and the tool form a single vertical line. Do not hold the metal so it forms an angle with the tool.
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Set a propane torch on a stable surface, open the gas valve and light the torch with a match. Adjust the torch flame until it is blue.
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Set a propane torch on a stable surface, open the gas valve and light the torch with a match. Adjust the torch flame until it is blue.
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Remove the steel from the flame when it begins to look pale yellow or brown. Steel goes through several color variations from "faint straw" to purple as it heats from about 400 degrees to about 500 degrees Fahrenheit.
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Set the hot steel on a cold anvil and allow the metal to slowly cool. Heating steel to just below 500 degrees and allowing it to slowly cool on an anvil is called "tempering."
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Reheat the steel in the flame until it begins to glow. Steel begins to emit photons at about 800 degrees. It begins to oxidize at that temperature and looks grey. At 1,000 degrees steel begins to glow faintly red.
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Heat the steel until it clearly glows cherry red. The steel is now at about 1,500 degrees.
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Immerse the cherry red steel into a 5-gallon metal bucket filled with 4 gallons of vegetable oil. Agitate the steel in the oil for about a minute and remove. Heating and quenching the steel has enhanced and preserved the crystalline structure of the metal and "hardened" it.
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References
Resources
- Photo Credit Photodisc/Photodisc/Getty Images
