First, If you are going to anneal gold and its alloys, I can not write a better description than what is already on the Hoover & Strong website. Please visit their website for a comprehensive guide to annealing gold. (This link opens in a new window.)
Work Hardened Jewelry Metals
If you’ve ever cold worked sheet or wire, you know what work hardening is. The further you reduce the metal thickness the harder it gets and less malleable it becomes. The same happens when you bend, flex, or hammer on metal. On a microscopic level, metal will show a grain structure similar a jar of large marbles. When the metal is annealed, these grains are large and can slide past each other. As the metal is worked, the grains break and become smaller and more packed together. If not annealed properly, the metal fractures or becomes too hard to work. being such a complex subject, This will be a page of its own soon. But it leads into this page about annealing.
When metal is hammered, bent, stressed, or otherwise “worked”, the molecules of the metal are pressed more closely together, causing it to lose flexibility. This is known as work-hardening. While we hammer our metal for jewelry, the metal will become progressively harder. If we do not stop to soften, or anneal, the metal, it will crack or split.
How will you know when it’s time to anneal?
- Listen to the sound when you are hammering. Soft metal makes a duller thud than hardened metal, which rings.
- This takes a bit of practice, but you will learn when your metal has hardened by the way your hammer bounces when you hit your metal. it is a subtle difference, but on annealed metals, your hammer sinks into softer metal, and as the metal hardens, the hammer will begin to bounce and make a higher pitched sound with each strike.
- Watch the metal change. Annealed metals change shape easily becoming flatter or longer, responding to the pressure of the hammer. Hard metal will resist your hammer strikes and want to retain their shape.
- Test the metal by trying to bend it when you notice the above signs of work hardening. If the metal is hard, springy or difficult to bend, STOP hammering and ANNEAL the metal.
What is annealing, and why is it important?
This is a process used to restore ductility to work-hardened metals. For most metal workers it may make seem pointless to discuss; however, there are some facts that will help you better understand the process and what is happening.
The annealing process is best described as having three stages.
- Increasing temperature
- Grain growth.
I will try to keep the science jargon to a minimum but some technical words will be needed to explain what is happening. If you have any questions, please let me know via email. The link is at the bottom of every page.
The process begins with a work-hardened piece of metal that has had the grain structure changed by working in some manner. Annealing is the process of heating until the grain structure changes back to the state it was before it was work hardened. These small changes in grain structure can be observed under very high magnification.
To achieve full annealing, heat the metal high enough for the recrystallization stage to occur. You are heating the metal and encouraging new, small, strain-free grains. Growth of these new grains continues until the more fibrous structure of work hardening is replaced by this new microstructure.
As grains continue to grow in the final stage of the annealing process, ductility peaks. If annealing goes on for too long, though, grains grow at the expense of others. Do not over heat your metal! It is tempting to heat the metal "just a few seconds more" to make sure it is annealed, but that can lead to exceedingly large grain growth. This over-annealing will give you an "orange peel” effect on the surface of your metal which is very hard to remove.
Factors that may influence the stages of the annealing process include alloy composition, the amount of cold work to which the metal had been subjected, temperature, and time. Some important things to remember about annealing are the following:
- At least some cold work is required before nucleation and recrystallization can be effective. For pure metals, about 2 percent strain is necessary.
- Cold work increases the number of nuclei, which results in a smaller recrystallized grain size. Therefore, products should be given a minimum of 50 percent to a maximum of 75 percent reduction between annealings, since finer grain materials tend to have better mechanical properties.
- Temperature changes have a greater effect than time on recrystallization. Per Grimwade, in practice, if annealing is done in a furnace, the recommended times are typically around 30 minutes. Torch annealing at the bench requires slightly higher temperatures because times are much shorter.
- Before annealing silver, copper, brass, or bronze, coat the piece with boric acid and alcohol. This flux coating will reduce oxidation and help minimize cleanup.
- The trick to proper annealing is to bring the metal up to a hot enough temperature long enough to cause annealing. If the metal is still hard, most of the time the metal was not taken to a high enough temperature or the temperature was not held long enough.
Fire Scale Prevention
When any metal that contains copper (copper, brass, bronze, sterling silver) are heated in the presence of oxygen, oxides are quickly formed. Cupric Oxide (CuO) is a black layer on the surface of the metal that can usually be dissolved in pickle. Make sure you coat the entire item being heated. Copper is EXTREAMLY reactive in the presence of oxygen when heated. if you have a small spot not covered by a flux or firecoat, the fire scale will start there and expand UNDER your a flux or firecoat.
To prevent fire scale, coat the metal in a flux or firecoat to protect from oxidation. The most common flux is to use is Borax powder (sodium borate), which melts at 1367°F/742°C. You can also coat your metal with boric acid and alcohol. tightly seal the container with the and alcohol and move away from the area where you will be working BEFORE you light your torch. Allow the alcohol to dry on your piece before allying heat.
Annealing Sterling Silver
I am assuming you are already familiar with lighting and using your torch. As they vary quite a bit, these instructions are fairly generic and will work with most torches.
- Begin by warming the metal gently across entire surface. then bring your flame in closer until the point of the blue cone is about 1/4 inch from the metal. This is the hottest part of the flame.
- Continue to move your flame constantly, evenly raising the temperature of the entire piece. Don’t stop the flame on any one area as you can melt a hole through in a moment.
- When the marks you made with the sharpie disappear or the flux starts to melt and become clear, you are nearing the annealing temperature of the metal.
- You will want to watch for changes in color that indicate the temperature of your metal. If at all possible, try to turn down the lights where you are working so it is dim.
This is a difficult state to describe. When annealing your silver or other metals by torch, a good visual guide is:
|Metal Color||Metal Temperature|
|Cherry Red||1400° F|
|Bright Salmon Red||1600° F|
- When it begins to glow pink, you have generally achieved annealing temperature for sterling silver.
- If you turn the lights back on at this moment, you will see that the pink glow is not quite visible. There is, however, a particular look to the silver at this time. Again, this is a difficult state to describe.
- With practice, you will be able to “see” this internal glow and recognize the changes in color that indicate that annealing has probably occurred.
- Copper, brass, and bronze should be heated until their glow is visible with the lights on. Copper and brass should glow gently, while bronze should be made to glow brightly to anneal well.
- When you have reached annealing temperature, back the flame away from the metal about an inch or so, but continue to heat it gently to maintain your annealing temperature for about 60 seconds to fully anneal the metal.
- If sterling starts to glow so that it is visible in normal room light, you have usually exceeded the normal annealing temp, so pull the flame back and heat more gently for 60 sec. You may need to quench the metal and start over if this happens.
- Brass needs to be annealed for much longer than copper or silver, so keep it glowing for 60 to 120 seconds.
Important note: After you have heated your metal, be sure to quench sterling silver from a black heat. Otherwise, the slow cooling will age-harden the metal slightly.
Fire Scale Removal
Most fire scale is removed by pickling in an acidic solution of some sort. Vinegar, sodium bisulfate based solution (Sparex is the most common brand), or citric acid available in the canning row of any grocery store. It works best when heated. A common pickle pot used to hold and heat the solution is a used crock pot (Check goodwill for these). The pickle solution works best about 180°F/80°C.
Oxides that are harder to remove can be removed using 5% nitric acid. Fire scale is best removed from silver alloys using a dilute (10%) sulfuric acid solution.
Things to be aware of:
Wire will heat and anneal very quickly, and it is safer to coil the wire to protect it from overheating.
Sheet will take longer than wire. The thickness of the metal (gauge) and the size of the sheet or wire will make a significant difference in the annealing time.
If noting color changes just doesn’t work for you, Mark your metal with a permanent marker (such as a Sharpie). When the sharpie burns off, your metal is close to the correct temperature. Increase your heat a bit more, then pull the torch back a little to keep the heat at annealing temperature for 60 or more seconds. Let the metal cool to a black heat, and quench.
Once the metal is annealed, remove the heat and turn off the torch. Allow it to cool until the glow is gone (black heat), then remembering that it is still hot, carefully pick up the metal with your insulated tweezers or tongs, and drop it into a bowl of water to cool it. It will hiss a bit as you drop it in the water and this is normal.
You can now remove the metal from the water and dry it well using a paper towel and check for softness by gently bending the piece. If fully annealed, it should now bend easily. If not, anneal it again but this time allow the metal to get slightly hotter and hold it at this temperature for a longer period of time.
One last thing to remember. Sometimes things go south real fast. At some point, you will accidentally melt some metal. Don't stress about it. Look at the melted pieces / edges and see what you can do with them.
You did not make a mistake. You experimented with "Organic Design Elements".
Seriously. Many times these little "mistakes" become stunning pieces.