The aluminum wire used for bonsai has an anodized coating on it to make it aesthetically harmonize with the bark of the tree.This earth tone blends better with the bark and makes an extensively wired tree seems less unsightly.Because of this aluminum has become the preferred wire among Japanese azaleas growers. Azaleas have thin bark which damages easily. Softer aluminum is less inclined to injure these more delicate trees. In addition to its softness aluminum wire’s one great advantage is that it does not have to be annealed.