A good question!
"Bonsai Wire" usually refers to one of two types. Both of these are manufactured or treated for use in bonsai:
1) Anodized Aluminum wire - this is a bright aluminum wire that has been electrochemically treated to give it a copper color. Holding power is less than copper, but it is easier to manipulate for many. Other than the concealing color, it is just aluminum wire. There are some non-bonsai applications, but the wire is usually
anodized in bright colors for use in fashion or jewelry. Electronics applications involve usually clear anodization and fine sizes for speaker magnets and miniature motors, replacing the more time-consuming process of lacquering the wire to insulate the windings from one another.
2) Annealed Copper wire - copper wire that has been tempered by heat, either in a fire, or electrically, to make it easy to bend. After bending it firms up. It has a holding power that is 2-3 times the strength of an equivalent size aluminum wire. Annealed copper wire sometimes finds use in electronics (fine windings in motors and magnets), but the wire is usually very fine.
Both types of wire are available in various diameters for different tasks - fine wire for detail wiring, and larger sizes for bending trunks and limbs. The Japanese wire is usually measured in millimeters (mm) vs. and American wire may be measured in Gauge or AWG. Curious thing about the wire gauge is as the wire gets smaller, the gauge gets bigger.
There is some additional info in the ***FAQ*** on wiring. There are a couple of links on
bonsaiTALK Links in the Techniques -> Wiring section that explain how you can anneal your own wire.
Both Anodized Aluminum and Annealed Copper wires are available from TreeBay -
http://www.treebay.com/index.html?A=21
Regards,
Matt