An easy guide on how to soften and anneal metals
To define the annealing process in simple terms means to remove any stresses and return material to a soft and workable state, ie. making it more malleable.
This is especially so in metals that become work-hardened, like copper and brass, although brass can become very brittle and fracture easily, especially if it has been heated.
In steels, this annealing process is generally used to make the metal more pliable and less likely to fracture.
This annealing process can also be used on glass. In other words, if you have a material that turns liquid upon heating (disregarding the temperature for now) then there’s a good chance it can be annealed.
How To Anneal Copper
The copper should be clean and bright, otherwise oxides will form and become embedded in the surface on heat-up, and should be warmed up with what’s known in the UK as a blow-lamp – sometimes known as a blowtorch elsewhere (a kitchen stove will do this at a push for copper) generally rather than at a specific point, although copper tends to spread heat quickly through the metal.
Once a background heat is produced, when the metal shows different colors radiating away from the heat source, then you are looking for a dark red (plum color) reaching the part you want annealing – it’s like the colors of the rainbow moving from blue through to bright red as the hottest.
Once this occurs quickly immerse the copper you are annealing into a water bath, and that’s it. Job done!
The easy test to see if it has softened is to tap it with a screwdriver or something similar.
If you hear a ringing sound, the copper is still hard and needs to be annealed again. If the sound is dull then you have annealed the copper properly.
But don’t delay the quenching too much, otherwise, you will not achieve the annealed copper you were aiming for. By delaying, you are normalizing the copper, which means it is not soft enough to become pliable and can easily fracture if bent too rigorously.
Before you begin to work the copper you must remove any surface oxides that have formed with a wire brush, wire wool or emery cloth as these become embedded, spoiling the appearance, and are difficult to remove later.
How To Anneal Brass
Annealing brass is very similar to copper, although the temperature should be a little cooler.
What you are looking for as you apply the flame of your blow-lamp/torch onto the part to be annealed is the tell-tale colors again.
When the brass starts to show a blackened color, then is the time to quench it quickly before cleaning it up.
How To Anneal Aluminum (Aluminium)
Now here you need to be very careful as the difference in temperature between softening and melting is marginal.
If you try to anneal aluminum without cleaning the surface you will get to the stage when heating where the surface looks solid because of the surface oxides, but the inside will be turned into a liquid, meaning the piece you are heating will collapse once the surface tension is destroyed and you will have it quickly turning into a blob of aluminum.
To do it properly, clean up the metal first before coating it with household soap, directly from the bar, covering the area of the aluminum you need to anneal (any brand will do providing it is a solid household soap and there is no built-in conditioner for dry skin included).
With your blow-lamp set at a low heat, run it around the surface, warming the work up generally and make a point of not keeping your flame in one place for too long.
Keep warming it up until you see the soap turning black and then shut the heat off rapidly and dunk it in cool water.
Clean it up and the job’s done…
You can see here that rather than watching for colors like on the steel, brass and copper process, the signal is the start of the burning of the soap, meaning it has reached the right temperature.
How To Anneal Steel
Annealing steel is generally needed when you are dealing with heat hardened steels.
Steel generally needs to be heated to cherry red and allowed to cool down naturally, the slower the better.
Heating allows the molecules within the steel to align properly and the slow cooling keeps them aligned, that way making the steel softer and more easily worked.
Looking at a blacksmith and his forge you will see that while the metal is hot it can be shaped easily with a good clout because the molecules are in line.
When the workpiece has cooled after being beaten, the molecules are out of line and the metal is harder and more likely to fracture. Obviously the more impacts it receives the harder (and more brittle) it becomes.
This is what is known as ‘work hardening’!
How To Anneal Stainless Steel
To anneal stainless steel, basically softening it, requires a lot more heat (1900°F / 1000+°C) than annealing steel in that an orangey-red color needs to be achieved with your blow-lamp, but it also needs to be kept orange for at least ten minutes – preferably longer to do it properly.
It all depends on the size of the piece of stainless steel you want to anneal. Larger flat pieces will definitely warp as they need to be cooled very quickly to stop the chromium and the carbon bonding – it’s the chromium that makes it stainless – so be prepared to have to flatten the sheet out.
For small sections, this is not so much of a problem.
As with each of these options, it is best to start off with a pre-cleaned metal, that way you don’t need to be work-hardening the material by applying friction with cleaning after the softening process.