Proper use of wire is probably the most single important skill required for bonsai. The wire allows you to move a branch from here to there where it makes a more pleasing presentation on your tree. If you had the best of all possible worlds, the wire would be limp as a noodle when you applied it and would then become sufficiently hard that it would hold the tree branch just where you wanted it. And guess what? Copper wire does this.
As first reported in your newsletter a while ago, the marvelous property of copper was discovered about 8000 years ago by a man who was out hunting a nice fat wooly mammoth to take home to the wife and kids for dinner. As he was walking along, he found a piece of metal which he knew was copper because copper is one of the few metals that can occasionally be found in a pure state rather than as an ore. As you will see, he was a very smart hunter. He also immediately recognized that although the piece was in the form of a lump, he could pound it into a splendid point for his spear where it would make a much better point than the stone one he was using. He set about forming the spear point during his lunch. To his dismay, the more he pounded on the lump the harder it became until it was so hard that no amount of pounding would change the shape of the lump any further. Pounding on the lump was a lot of hard work, so he called the process work hardening. Whatever he called it, he was a long way from having a spear point. Disgusted, he threw the lump into the campfire where he had cooked his lunch.

A friend came by and asked him how things were going. After complaining about his favorite sports team, he told his friend about the lump he had found. He fished the lump out of the fire and when it cooled down, he showed his friend how hard it had become by pounding on it. To his astonishment the lump was soft again! After a bit of thought a light bulb came on. He reasoned that although the copper that he originally found was in the form of a lump, it actually had a highly regular face centered cubic crystal structure and this made the metal soft. Pounding on it disrupted the crystal structure, leading to a much harder form of the metal. (See, he was a very smart hunter). Further, heating the lump in his campfire allowed the lump to reestablish the regular crystal structure. He called this process annealing. His friend was delighted with the new finding of the hunter and together they formed a startup company which featured a whole catalogue of fine spear points.
Although all this happened 8,000 years ago, the hunter had a clear vision of the future. His marvelous discovery would allow the Egyptians to make hardened copper chisels to carve the stone blocks they used for their big architectural projects. He was saddened to see that copper would be replaced by iron tools which were easier to make and were harder that the copper ones. He looked even further into the future and was delighted to find the there was one area where his discovery would still be used. Iron wire will never replace copper wire for bonsai because iron wire is too stiff and rusts over time, staining the bark of the bonsai trees. He smiled, knowing that his discovery of the marvelous properties of copper would stand the test of time.
And there you have the true story of the origin of copper wire. There is one unanswered question that history does not shed light on. We do not know whether he bagged a nice fat wooly mammoth as dinner for his wife and kids.
When we buy copper wire for our bonsai we make use of the technology our hunter discovered 8,000 years ago. The wire is relatively soft because it has been annealed by heating it under very carefully controlled conditions of time and temperature. Sometimes the purchased wire is coated with a flaky black residue on the surface. This is copper oxide which was formed in the heating process.
Annealed copper wire becomes work hardened by simply bending it. As we apply wire to our trees, the wire hardens by bending it around the branches. Fortunately you don’t have to pound on it before it hardens. The resulting increase in rigidity of the wire makes positioning the branch easier and holds the branch in place until it grows strong enough to hold the position without the help of wire.
When you are wiring your tree, a common mistake is to remove a piece of wire from the coil and straighten it before you apply it to the tree. Straightening the wire hardens it before you wrap it around the branch, and this makes it more difficult to use.
In principle, you can anneal copper wire that has been removed from a tree by heating it with a propane torch to a dull red color. It is a lot of work because you have to first straighten the wire. When the wire cools, it is annealed. Heating with a torch is difficult to control and when you are done you have a relatively short piece of wire. It is a lot of work and most people are happy to buy the wire ready for use.
Aluminum wire is also used for wiring bonsai and it, too, can be annealed and work hardens when used, but each process occurs to a far lesser degree than for copper.