Comparison Al-Cu

For bonsai styling, especially bonsai wire made of aluminum or copper is used. Rarely also steel wire. Before buying bonsai wire, it is good to know the pros and cons. Here we have put together a comparison of the properties of the wire types.

Our, admittedly somewhat simple, assessment or recommendation is: Steer clear of steel, aluminum bonsai wire is good for beginners, copper wire is the best choice for the bonsai professional.

Aluminum

Main advantage: Can easily be corrected -> good for beginner
Main disadvantage: It requires comparatively thick wire thickness -> more noticeable on a bonsai tree
Disadvantage: Sometimes the anodization bleaches over the years. But rarely does an aluminum bonsai wire stay so long on the tree.
Advantage: Good and cheap aluminum bonsai wire is available at almost every bonsai dealer

Bonsai wire cutter

Copper

Main advantage: Annealed easily bendable, then ever harder -> thin wire gauge sufficient
Main disadvantage: Heavier correctable, difficult to unwind (bonsai wire cutter required for unwiring)
Disadvantage: Good bonsai wire made of copper is difficult to obtain
Note: Low concentrations of copper appear to decrease node spacing on some bonsai species. But - the story that a copper nail in the tree leads to dieback seems to be a gardening fairy tale

Steel

Main advantage: Very cheap
Main disadvantage: Difficult to bend, stiff -> Difficult to wrap on, hardly any tight bends possible
Disadvantage: Rust -> long visible on bark
Not commonly used or offered in Europe. Is not recommended. Is mainly used in china for bonsai production

Comparison of prices

With the same weight and wire thickness, copper has a much shorter length than aluminum wire
In addition, aluminum is about 20% cheaper than copper wire
Is copper wire sensible from a cost point of view ?
With the same branch thickness, the copper bonsai wire used can be about half as thick as the aluminum wire
Example: A 2.0mm copper wire is equivalent to a 3.5mm aluminum wire. The copper wire is approx. 42m long, the aluminum wire 38m long. Price difference at the end of the bill only about 10%
Scrap metal price is significantly higher for copper. The price difference is then almost balanced

Anneal copper wire

Copper wire changes its strength by bending and annealing at high temperatures.

Crystal structure changes due to high temperatures -> atoms move -> reorientation -> even distances -> wire becomes softer, more flexible
Bending disrupts the crystal structure -> Wire becomes stiff and hard like iron -> Hard to bend back, holds the shape for many years
Buying bonsai wire: Big reels are said not to become so stiff when unwinding
Copper wire annealing: Between 400°C and 650°C. Good are pottery stoves with temperature computers. If possible, annealing in a low-oxygen atmosphere
Caution: If copper bonsai wire is annealed too high or too long, the wire later crumbles during wiring of a bonsai (internal oxidation)
Attention: Too low or too short annealed: The copper bonsai wire is not soft enough and can be difficult to wrap arround the branch