The Science of Work Hardening and Annealing

I had the wonderful opportunity a couple weeks ago to work with Iowa State University Program for Women in Science and Engineering K-12 Outreach Program. They have several opportunities throughout the year for young girls to experience activities that create an interest in science, technology, engineering and math. So they contacted the ISU Memorial Union Workspace where I teach metalsmithing classes and we developed an activity so they could make something and learn something and hopefully even gain some self confidence!

I chose Foldformed Copper Bangles as their project. They turned out great!

These are samples I created for the class

Each of the 54 participants (ages 8-14 in 4 groups) received a 6x1 inch strip of 26 gauge copper. I used 26 gauge because I wanted to be sure that the youngest girls could be successful hammering and unfolding their bangles.  It worked great and if we did it again I think we will use 24 gauge, although 26 is a bit cheaper.

Now the Science

Copper is an element found on the Periodic Table of Elements.  It is a noble metal. It is made up of atoms that line up in a regular pattern that repeats, forming a crystalline structure.  Copper can be soft and it can be hard. Metals can be made stronger by deforming the crystalline structure of the molecules. This is what happens when you hit copper with your hammer. You change the molecular structure of the copper and make it hard. --Work Hardening --  To make the copper soft again, you Anneal the copper.

So as you hammer away on your beautiful copper, you notice it gets stiffer, harder to bend and the sound of your hammering will become higher pitched. The molecular arrangement of the copper has been deformed thus making the copper stronger. If you continue to hammer, the copper will become harder but also brittle. This is why paper clips are easy to break. The metal is hard, but brittle. I also learned from the ISU Engineering Students who were helping the reason why the Titanic broke into two pieces. Apparently the metal that formed the ship was too hard and brittle and that is why the ship broke in two and sunk. wow.

I later watched a documentary on the Titanic and not only was the metal too brittle but the rivets of the Titanic were made of a weaker iron in the front and rear of the ship. When the ship hit the iceberg with the bow, the rivets did not hold and six seams came apart on the ship. The weakness came because there was a larger amount of slag in the iron that made up the rivets. Slag weakens the metal and in tests, metal with a higher amount of slag will not stretch as far and is more brittle than metal with less slag. I also watched a NOVA documentary about the making of viking swords. It was very interesting and helped me to understand more about work hardening and annealing and what happens at the molecular level of the metal. A sword is made of steel and worked by a blacksmith but educating yourself on a variety of art forms only adds to your own knowledge. Also the blacksmith was from nearby Wisconsin and I am now a fan. His knowledge and workmanship was remarkable. Here is a link to the NOVA episode: http://www.pbs.org/wgbh/nova/ancient/secrets-viking-sword.html

Annealing is the process of heating your copper up which helps the copper molecules get back into their nice, tidy, crystalline structure and like magic it is soft again.  I don't know about you but this blows my mind.  I love how you can work with copper over and over and over again and as long as you are careful while annealing you can work with it indefinitely.

When you anneal the copper, turn off your lamp that you use in your torch area. Dim light helps you see the color change of the copper, and that tells you the temperature of the copper. Heat your copper to a dull red. Keep it at a dull red for 10-15 seconds. To do this, keep moving your torch around and over your piece. I have to move the flame off the piece so I can see the color of the metal. You will see that the copper will first start to turn dark and then the dull red. When you move the flame away the dull red will quickly disappear as the metal instantly starts to cool. Immediately put your flame to the metal again, making passes over the metal and watching the color. Then turn off your torch and quench your piece.  Be careful though because dull red can quickly turn to bright red and that is too hot.

If you heat your copper to bright red you risk making your copper very hard -the complete opposite of annealing! So watch the color change very closely. Practice on scrap and have fun!

Trying Out Patinas

Turning Copper Green and Blue

Patina is what happens to copper and silver and other metals over time. The color of the metal changes because of the chemical reactions between the metal and the environment.  It takes many years for copper to turn green, especially where I am from in Iowa. I discovered this a few years ago when I made a rain chain for my mother-in-law and the copper turned very dark and even black in some places.  Eventually it will get some green but now I know how to speed up the process!

I have had a lot of fun learning about how to speed up patinas on copper. I have to give thanks to all the free information on the internet and in my books and hopefully this information will help you too.   After researching many recipes, I found some that I thought I could actually try with stuff I had in the house. I also wanted to work with ingredients that were not toxic and I really like the idea of creating the recipe myself as opposed to buying a jar of something pre-made. Please share what you have tried and let me know your results.

Ammonia, vinegar and salt and surprisingly saw dust are the ingredients used in different combinations to get copper to turn green or blue/green.  So far, they all turned out great, but I can generally scratch off the green with my fingernail so all material will probably need to be coated with a lacquer.

Buried Patina:
*I apologize that I can not find the actual web site that I found this information from, however I have found many others with slight variations of the bury method.  I will keep looking because I want to link to the site so the proper person gets credit. Even though she didn't invent the method but like me was just passing the information along in her blog.

 If you want a textured patina try easy, kitchen friendly Buried Patina For Blue color on copper: Add 1 part Vinegar to 4 parts Ammonia and saturate hardwood sawdust until media clumps together in a sandwich size zip-lock baggie filled with saw dust. Bury metal in media and seal the bag. Place in a warm spot and check each day to see if the color appears and is to your liking. When the color is right for you, let the piece dry out before using or sealing.  The "texture" comes from where the saturated sawdust comes in contact with the copper.

For Green color on copper: Add 1 part Vinegar to 3 parts Ammonia and saturate until media clumps together in a sandwich size zip-lock baggie filled sawdust or rolling tobacco. Bury metal in media and seal the bag. Place in a warm spot and check each day to see if the color appears and is to your liking.

For Bright turquoise color on copper:  Add 1 cup ammonia, 1 cup rock salt, ½ cup tap water to cotton squares until media clumps together and bury metal, seal bag, place in warm area, check each day

If you want a transparent patina to be able to see textures or etching try Liver of Sulphur (LOS) or other transparent patinas.Some of the above info came from books by Jinks McGrath

Painting vinegar/salt and ammonia/salt on copper works too. I simply painted the liquid on the copper, let it dry and reapplied. I did this at least three times and came up with some great results.

I was able to remove some of the patina with my fingernail. You can resolve this by working with  this method longer and making more applications and then seal the copper with lacquer or a fixative.

Ammonia with salt also gave a similar shade of green. This was really fun!