Annealing is a heat treatment during which the metal is altered, causing changes in its strength and hardness. Annealing is used to relieve internal stresses and increase ductility, thereby improving cold working properties. Metal will work harden when it is worked using cold forming processes such as compressing, bending, drawing, or shearing. During these operations, the metal will become progressively harder. If the metal is not annealed periodically, it may crack or split. The annealing process involves heating the material to a high temperature (1100-1200°F) for a while and then allowing it to cool. Ferrous metals must be cooled slowly to anneal; but brass, copper and silver can be quenched in water. After annealing the metal is softened and prepared for further cold forming. Signs that can indicate that you should anneal your work include:
- Additional force - It takes more force for the hammer to deform the metal. The hammer will also bounce off work hardened metal.
- Change in sound - Work hardened metal makes a bright ringing noise when struck sharply with a hammer.
- Slower work rate - Hard metal will resist change, and may even spring back when trying to shape it.
If the metal displays any of these signs, you should stop forming your work and anneal it. Failure to do so may result in splits or cracks forming. A good visual guide for temperature when working with sterling silver is:
- Visibly Red - 900°F (482°C)
- Dull Red - 1200°F (649°C)
- Cherry Red - 1400°F (760°C)
- Bright Salmon Red - 1600°F (871°C)
How to Anneal
- Work in subdued lighting conditions, it will make it easier to see subtle changes of colour as the metal heats up.
- Place the hardened metal on the hearth.
- Use a torch with a soft, bushy flame. A slight excess of fuel will help to burn off oxygen and reduce oxidation.
- Warm the metal gently across the whole surface.
- Move the flame closer, about ¼" from the surface of the metal.
- Move the flame evenly over the metal, avoid lingering on any one spot. When annealing wire, it will be easier to maintain an even temperature over the entire piece if it is coiled.
- When silver glows a dull pink, the correct temperature will have been attained.
- Brass and copper will glow more brightly, and the effect will be visible even in good lighting conditions.
- Once the correct temperature is reached, move the flame away slightly so that the temperature is maintained but does not increase.
- Maintain the heat for approximately 1 minute for silver or copper, and 1½ - 2 minutes for brass.
- Remove the flame and turn off the torch.
- After a few seconds, carefully pick up the metal with tweezers. Ensure that you have a secure grip, but not too tight otherwise you may mark the metal.
- Quench the metal in water, then pickle. Do not quench in pickle as this will spit acid and release noxious fumes. If you leave silver to air cool it will be marginally harder.
- Dry the metal before you re-commence forming it, otherwise the damp will rust your tools.
