Copper vs Aluminum

Copper vs Aluminum Bonsai Training Wire

Wire is an important aspect of bonsai techniques. At stores, there are wires of many different materials and of many price points and geographical origins That begs the question: copper or aluminum?

Copper was used before. But things are changing. Bonsai masters have always used annealed wire copper.

We have just started to use aluminum for some deciduous trees, but it is much more easy and cheap. I am clearly biased, but here are what I feel are the important considerations:

Annealed Copper

  • More expensive
  • Work hardens as it is applied, so it holds better than aluminum
  • Preferred for conifers
  • Cannot be reused unless reannealed

Anodized Aluminum

  • Cheapter
  • Softer than copper, it has to be perhaps 1/3 larger in diameter than copper for a given purpose. The larger diameter has a larger “foot print”, or contact area, with the bark, so it will be slower to scar a delicate barked tree
  • Many bonsaists prefer aluminum for deciduous trees
  • Aluminum doesn’t work harden very much, so it can be reused

Coils Size

Tian bonsai tool makes wire into conveniently sized coils that are not too big and not too small.

And they make the smaller wires in smaller diameter coils that are easier to handle and are less likely to become tangled “bird nests”.

Japanese vs Chinese bonsai wire

Japanese wire is of excellent quality. But the Tian Bonsai aluminum wire is annealed too and better than other domestic wires, but I do not expect it to be any better than the Japanese wire.

Customers loved it! Both the quality (not all “annealed” wire is as soft as Tian; I have heard of unevenly annealed wire that has hard and soft spots) and the price, because my wire was less than half of the price of imported copper wire.

Storing Copper Wire

There are two considerations: convenience and protecting the wire from being deformed (and therefore hardened) before you use it.

You may have more elegant ideas, but I recommend storing and carrying your annealed wire in a cardboard box. A 12” x 12” x 6” box will easily hold one coil of each size.

For most people, however, the wire box gets jostled around and the heavy wires beat up the small wires, so you should separate the 4 smallest sizes from the larger wires.

You could use a separate box, or make a topless cardboard tray about 8 inches square by 1 1/2 inches high.

Put the small wires in the tray and carry the tray inside your wire box, on top of the heavier wire.

I use a more elaborate version. I made nesting trays – one tray for each wire size – so none of the wires get tangled with the others. The trays keep my wires separate and undeformed for maximum softness.

Why Anneal?

Annealing is the process of heating metal to make it softer. The effect is particularly strong for copper, so annealed copper is much, much, much softer than unannealed copper.

Bending annealed copper wire causes it to work hard, which reverses the annealing. Annealed copper is soft when we apply it to our trees and it gets much harder with time.

This is sort of magical and is the main reason that copper wire is often superior to aluminum wire for bonsai: The wire is soft going on, but it gets harder in the process and thereby holds the branch or trunk as if it were a much larger wire! But, we don’t want the wire to harden before it gets to the tree.

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bonsai wire cutter

So to minimize ‘pre-wiring hardening’, users should (a) protect the wire from deformation in storage, travel, etc. – don’t let it get knocked around – and (b) minimize the hardening that occurs as a piece is straightened from the coil just before using.

This is nearly insignificant for very thin wires, but very important for heavy wires – they will be dramatically hardened if they are annealed in small diameter coils then straightened out for application.

So I make heavy wires into large diameter coils and fine wires into smaller diameter coils.

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